## 1. History of the issue




Questions about the nature of conscious awareness have likely been
asked for as long as there have been humans. Neolithic burial practices
appear to express spiritual beliefs and provide early evidence for at
least minimally reflective thought about the nature of human
consciousness (Pearson 1999, Clark and Riel-Salvatore 2001).
Preliterate cultures have similarly been found invariably to embrace
some form of spiritual or at least animist view that indicates a degree
of reflection about the nature of conscious awareness.




Nonetheless, some have argued that consciousness as we know it today
is a relatively recent historical development that arose sometime after
the Homeric era (Jaynes 1974). According to this view, earlier humans
including those who fought the Trojan War did not experience themselves
as unified internal subjects of their thoughts and actions, at least
not in the ways we do today. Others have claimed that even during the
classical period, there was no word of ancient Greek that corresponds
to "consciousness" (Wilkes 1984, 1988, 1995). Though the
ancients had much to say about mental matters, it is less clear whether
they had any specific concepts or concerns for what we now think of as 
consciousness.




Although the words "conscious" and
"conscience" are used quite differently today, it is likely
that the Reformation emphasis on the latter as an inner source of truth
played some role in the inward turn so characteristic of the modern
reflective view of self. The Hamlet who walked the stage in 1600
already saw his world and self with profoundly modern eyes.




By the beginning of the early modern era in the seventeenth century,
consciousness had come full center in thinking about the mind. Indeed
from the mid-17th through the late 19th century, consciousness was
widely regarded as essential or definitive of the mental. Rene
Descartes defined the very notion of thought (*pensee*) in terms of
reflexive consciousness or self-awareness. In the *Principles of
Philosophy* (1640) he wrote,



> By the word 'thought'
> ('*pensee*') I understand all that of which we are
> conscious as operating in us.




Later, toward the end of the 17th century, John Locke offered a
similar if slightly more qualified claim in *An Essay on Human
Understanding* (1688),



> I do not say there is no soul in man because he is not
> sensible of it in his sleep. But I do say he can not think at any time,
> waking or sleeping, without being sensible of it. Our being sensible of
> it is not necessary to anything but our thoughts, and to them it is and
> to them it always will be necessary.




Locke explicitly forswore making any hypothesis about the
substantial basis of consciousness and its relation to matter, but he
clearly regarded it as essential to thought as well as to personal
identity.




Locke's contemporary G.W. Leibniz, drawing possible inspiration from
his mathematical work on differentiation and integration, offered a
theory of mind in the *Discourse on Metaphysics* (1686) that
allowed for infinitely many degrees of consciousness and perhaps even
for some thoughts that were unconscious, the so called "petites
perceptions". Leibniz was the first to distinguish explicitly
between perception and apperception, i.e., roughly between awareness
and self-awareness. In the *Monadology* (1720) he also offered
his famous analogy of the mill to express his belief that consciousness
could not arise from mere matter. He asked his reader to imagine
someone walking through an expanded brain as one would walk through a
mill and observing all its mechanical operations, which for Leibniz
exhausted its physical nature. Nowhere, he asserts, would such an
observer see any conscious thoughts.




Despite Leibniz's recognition of the possibility of unconscious
thought, for most of the next two centuries the domains of thought and
consciousness were regarded as more or less the same. Associationist
psychology, whether pursued by Locke or later in the eighteenth century
by David Hume (1739) or in the nineteenth by James Mill (1829), aimed
to discover the principles by which conscious thoughts or ideas
interacted or affected each other. James Mill's son, John Stuart Mill
continued his father's work on associationist psychology, but he
allowed that combinations of ideas might produce resultants that went
beyond their constituent mental parts, thus providing an early model of
mental emergence (1865).




The purely associationist approach was critiqued in the late
eighteenth century by Immanuel Kant (1787), who argued that an adequate
account of experience and phenomenal consciousness required a far
richer structure of mental and intentional organization. Phenomenal
consciousness according to Kant could not be a mere succession of
associated ideas, but at a minimum had to be the experience of a
conscious self situated in an objective world structured with respect
to space, time and causality.




Within the Anglo-American world, associationist approaches continued
to be influential in both philosophy and psychology well into the
twentieth century, while in the German and European sphere there was a
greater interest in the larger structure of experience that led in
part to the study of phenomenology through the work of Edmund Husserl
(1913, 1929), Martin Heidegger (1927), Maurice Merleau-Ponty (1945) and
others who expanded the study of consciousness into the realm of the
social, the bodily and the interpersonal.




At the outset of modern scientific psychology in the mid-nineteenth
century, the mind was still largely equated with consciousness, and
introspective methods dominated the field as in the work of Wilhelm
Wundt (1897), Hermann von Helmholtz (1897), William James (1890) and
Alfred Titchener (1901). However, the relation of consciousness to
brain remained very much a mystery as expressed in T. H. Huxley's
famous remark,



> How it is that anything so remarkable as a state of
> consciousness comes about as a result of irritating nervous tissue, is
> just as unaccountable as the appearance of the Djin, when Aladdin
> rubbed his lamp (1866).




The early twentieth century saw the eclipse of consciousness from
scientific psychology, especially in the United States with the rise of
behaviorism (Watson 1924, Skinner 1953) though movements such as
Gestalt psychology kept it a matter of ongoing scientific concern in
Europe (Kohler 1929, Koffka 1935). In the 1960s, the grip of
behaviorism weakened with the rise of cognitive psychology and its
emphasis on information processing and the modeling of internal mental
processes (Neisser 1965, Gardiner 1985). However, despite the renewed
emphasis on explaining cognitive capacities such as memory, perception
and language comprehension, consciousness remained a largely neglected
topic for several further decades.




In the 1980s and 90s there was a major resurgence of scientific and
philosophical research into the nature and basis of consciousness
(Baars 1988, Dennett 1991, Penrose 1989, 1994, Crick 1994, Lycan 1987,
1996, Chalmers 1996). Once consciousness was back under discussion,
there was a rapid proliferation of research with a flood of books and
articles, as well as the introduction of specialty journals (*The
Journal of Consciousness Studies, Consciousness and Cognition,
Psyche)*, professional societies (Association for the Scientific
Study of Consciousness--ASSC) and annual conferences devoted
exclusively to its investigation ("The Science of
Consciousness").


## 2. Concepts of Consciousness




The words "conscious" and "consciousness"
are umbrella terms that cover a wide variety of mental phenomena. Both
are used with a diversity of meanings, and the adjective
"conscious" is heterogeneous in its range, being applied
both to whole organisms--creature consciousness--and to
particular mental states and processes--state consciousness
(Rosenthal 1986, Gennaro 1995, Carruthers 2000).


### 2.1 Creature Consciousness




An animal, person or other cognitive system may be regarded as
conscious in a number of different senses.



*Sentience.* It may be conscious in the generic sense of
simply being a *sentient* creature, one capable of sensing and
responding to its world (Armstrong 1981). Being conscious in this sense
may admit of degrees, and just what sort of sensory capacities are
sufficient may not be sharply defined. Are fish conscious in the
relevant respect? And what of shrimp or bees?



*Wakefulness.* One might further require that the organism
actually be exercising such a capacity rather than merely having the
ability or disposition to do so. Thus one might count it as conscious
only if it were *awake and normally alert.* In that sense
organisms would not count as conscious when asleep or in any of the
deeper levels of coma. Again boundaries may be blurry, and intermediate
cases may be involved. For example, is one conscious in the relevant
sense when dreaming, hypnotized or in a fugue state?



*Self-consciousness.* A third and yet more demanding sense
might define conscious creatures as those that are not only aware but
also aware that they are aware, thus treating creature consciousness as
a form of *self-consciousness* (Carruthers 2000). The
self-awareness requirement might get interpreted in a variety of ways,
and which creatures would qualify as conscious in the relevant sense
will vary accordingly. If it is taken to involve explicit conceptual
self-awareness, many non-human animals and even young children might
fail to qualify, but if only more rudimentary implicit forms of
self-awareness are required then a wide range of nonlinguistic
creatures might count as self-conscious.



*What it is like.* Thomas Nagel's (1974)
famous*"what it is like"* criterion aims to capture
another and perhaps more subjective notion of being a conscious
organism. According to Nagel, a being is conscious just if there is
"something that it is like" to be that creature, i.e., some
subjective way the world seems or appears from the creature's mental or
experiential point of view. In Nagel's example, bats are conscious
because there is something that it is like for a bat to experience its
world through its echo-locatory senses, even though we humans from our
human point of view can not emphatically understand what such a mode of
consciousness is like from the bat's own point of view.



*Subject of conscious states.* A fifth alternative would be
to define the notion of a conscious organism in terms of conscious
states. That is, one might first define what makes a mental state a
conscious mental state, and then define being a conscious creature in
terms of having such states. One's concept of a conscious organism
would then depend upon the particular account one gives of conscious
states (section 2.2).



*Transitive Consciousness.* In addition to describing
creatures as conscious in these various senses, there are also related
senses in which creatures are described as being *conscious of*
various things. The distinction is sometimes marked as that between
*transitive* and *intransitive* notions of consciousness,
with the former involving some object at which consciousness is
directed (Rosenthal 1986).


### 2.2 State consciousness




The notion of a conscious mental state also has a variety of
distinct though perhaps interrelated meanings. There are at least six
major options.



*States one is aware of.* On one common reading, a conscious
mental state is simply a mental state one is aware of being in
(Rosenthal 1986, 1996). Conscious states in this sense involve a form
of *meta-mentality* or *meta-intentionality* in so far as
they require mental states that are themselves about mental states. To
have a conscious desire for a cup of coffee is to have such a desire
and also to be simultaneously and directly aware that one has such a
desire. Unconscious thoughts and desires in this sense are simply
those we have without being aware of having them, whether our lack of
self-knowledge results from simple inattention or more deeply
psychoanalytic causes.



*Qualitative states.* States might also be regarded as
conscious in a seemingly quite different and more *qualitative*
sense. That is, one might count a state as conscious just if it has or
involves qualitative or experiential properties of the sort often
referred to as "qualia" or "raw sensory feels".
(See the entry on
 qualia.)
 One's perception of the Merlot one is drinking or of the fabric one
is examining counts as a conscious mental state in this sense because
it involves various sensory qualia, e.g., taste qualia in the wine
case and color qualia in one's visual experience of the cloth. There
is considerable disagreement about the nature of such qualia
(Churchland 1985, Shoemaker 1990, Clark 1993, Chalmers 1996) and even
about their existence. Traditionally qualia have been regarded as
intrinsic, private, ineffable monadic features of experience, but
current theories of qualia often reject at least some of those
commitments (Dennett 1990).



*Phenomenal states.* Such qualia are sometimes referred to as
phenomenal properties and the associated sort of consciousness as
*phenomenal* consciousness, but the latter term is perhaps more
properly applied to the overall structure of experience and involves
far more than sensory qualia. The phenomenal structure of consciousness
also encompasses much of the spatial, temporal and conceptual
organization of our experience of the world and of ourselves as agents
in it (see section
 4.3).
 It is therefore probably
best, at least initially, to distinguish the concept of phenomenal
consciousness from that of qualitative consciousness, though they no
doubt overlap.



*What-it-is-like states.* Consciousness in both those senses
links up as well with Thomas Nagel's (1974) notion of a conscious
creature, insofar as one might count a mental state as conscious in the
*"what it is like*" sense just if there is something
that it is like to be in that state. Nagel's criterion might be
understood as aiming to provide a first-person or internal conception
of what makes a state a phenomenal or qualitative state.



*Access consciousness.* States might be conscious in a
seemingly quite different access sense, which has more to do with
intra-mental relations. In this respect, a state's being conscious is a
matter of its availability to interact with other states and of the
access that one has to its content. In this more functional sense,
which corresponds to what Ned Block (1995) calls *access
consciousness,* a visual state's being conscious is not so much a
matter of whether or not it has a qualitative "what it's
likeness", but of whether or not it and the visual information
that it carries is generally available for use and guidance by the
organism. In so far as the information in that state is richly and
flexibly available to its containing organism, then it counts as a
conscious state in the relevant respect, whether or not it has any
qualitative or phenomenal feel in the Nagel sense.



*Narrative consciousness.* States might also be regarded as
conscious in a *narrative* sense that appeals to the notion of
the "stream of consciousness", regarded as an ongoing more
or less serial narrative of episodes from the perspective of an actual
or merely virtual self. The idea would be to equate the person's
conscious mental states with those that appear in the stream (Dennett
1991, 1992).




Although these six notions of what makes a state conscious can be
independently specified, they are obviously not without potential
links, nor do they exhaust the realm of possible options. Drawing
connections, one might argue that states appear in the stream of
consciousness only in so far as we are aware of them, and thus forge a
bond between the first meta-mental notion of a conscious state and the
stream or narrative concept. Or one might connect the access with the
qualitative or phenomenal notions of a conscious state by trying to
show that states that represent in those ways make their contents
widely available in the respect required by the access notion.




Aiming to go beyond the six options, one might distinguish conscious
from nonconscious states by appeal to aspects of their intra-mental
dynamics and interactions other than mere access relations; e.g.,
conscious states might manifest a richer stock of content-sensitive
interactions or a greater degree of flexible purposive guidance of the
sort associated with the self-conscious control of thought.
Alternatively, one might try to define conscious states in terms of
conscious creatures. That is, one might give some account of what it is
to be a conscious creature or perhaps even a conscious self, and then
define one's notion of a conscious state in terms of being a state of
such a creature or system, which would be the converse of the last
option considered above for defining conscious creatures in terms of
conscious mental states.


### 2.3 Consciousness as an entity




The noun "consciousness" has an equally diverse range of
meanings that largely parallel those of the adjective
"conscious". Distinctions can be drawn between creature and
state consciousness as well as among the varieties of each. One can
refer specifically to phenomenal consciousness, access consciousness,
reflexive or meta-mental consciousness, and narrative consciousness
among other varieties.




Here consciousness itself is not typically treated as a substantive
entity but merely the abstract reification of whatever property or
aspect is attributed by the relevant use of the adjective
"conscious". Access consciousness is just the property of
having the required sort of internal access relations, and qualitative
consciousness is simply the property that is attributed when
"conscious" is applied in the qualitative sense to mental
states. How much this commits one to the ontological status of
consciousness per se will depend on how much of a Platonist one is
about universals in general. (See the entry on
 the medieval problem of universals.)
 It need not commit one to consciousness as a distinct entity any more
than one's use of "square", "red" or
"gentle" commits one to the existence of squareness,
redness or gentleness as distinct entities.




Though it is not the norm, one could nonetheless take a more
robustly realist view of consciousness as a component of reality. That
is one could think of consciousness as more on a par with
electromagnetic fields than with life.




Since the demise of vitalism, we do not think of life *per
se* as something distinct from living things. There are living
things including organisms, states, properties and parts of organisms,
communities and evolutionary lineages of organisms, but life is not
itself a further thing, an additional component of reality, some vital
force that gets added into living things. We apply the adjectives
"living" and "alive" correctly to many things,
and in doing so we might be said to be attributing life to them but
with no meaning or reality other than that involved in their being
living things.




Electromagnetic fields by contrast are regarded as real and
independent parts of our physical world. Even though one may sometimes
be able to specify the values of such a field by appeal to the behavior
of particles in it, the fields themselves are regarded as concrete
constituents of reality and not merely as abstractions or sets of
relations among particles.




Similarly one could regard "consciousness" as referring
to a component or aspect of reality that manifests itself in conscious
states and creatures but is more than merely the abstract
nominalization of the adjective "conscious" we apply to
them. Though such strongly realist views are not very common at
present, they should be included within the logical space of
options.




There are thus many concepts of consciousness, and both
"conscious" and "consciousness" are used in a
wide range of ways with no privileged or canonical meaning. However,
this may be less of an embarrassment than an embarrassment of riches.
Consciousness is a complex feature of the world, and understanding it
will require a diversity of conceptual tools for dealing with its many
differing aspects. Conceptual plurality is thus just what one would
hope for. As long as one avoids confusion by being clear about one's
meanings, there is great value in having a variety of concepts by which
we can access and grasp consciousness in all its rich complexity.
However, one should not assume that conceptual plurality implies
referential divergence. Our multiple concepts of consciousness may in
fact pick out varying aspects of a single unified underlying mental
phenomenon. Whether and to what extent they do so remains an open
question.


## 3. Problems of Consciousness




The task of understanding consciousness is an equally diverse
project. Not only do many different aspects of mind count as conscious
in some sense, each is also open to various respects in which it might
be explained or modeled. Understanding consciousness involves a
multiplicity not only of explananda but also of questions that they
pose and the sorts of answers they require. At the risk of
oversimplifying, the relevant questions can be gathered under three
crude rubrics as the What, How, and Why questions:


* The Descriptive Question: *What* is consciousness? What are
its principal features? And by what means can they be best discovered,
described and modeled?
* The Explanatory Question: *How* does consciousness of the
relevant sort come to exist? Is it a primitive aspect of reality, and
if not how does (or could) consciousness in the relevant respect arise
from or be caused by nonconscious entities or processes?
* The Functional Question: *Why* does consciousness of the
relevant sort exist? Does it have a function, and if so what is it?
Does it act causally and if so with what sorts of effects? Does it make a
difference to the operation of systems in which it is present, and if
so why and how?




The three questions focus respectively on describing the features of
consciousness, explaining its underlying basis or cause, and
explicating its role or value. The divisions among the three are of
course somewhat artificial, and in practice the answers one gives to
each will depend in part on what one says about the others. One can
not, for example, adequately answer the what question and describe the
main features of consciousness without addressing the why issue of its
functional role within systems whose operations it affects. Nor could
one explain how the relevant sort of consciousness might arise from
nonconscious processes unless one had a clear account of just what
features had to be caused or realized to count as producing it. Those
caveats notwithstanding, the three-way division of questions provides a
useful structure for articulating the overall explanatory project and
for assessing the adequacy of particular theories or models of
consciousness.


## 4. The descriptive question: *What* are the features of consciousness?




The *What* question asks us to describe and model the
principal features of consciousness, but just which features are
relevant will vary with the sort of consciousness we aim to capture.
The main properties of access consciousness may be quite unlike those
of qualitative or phenomenal consciousness, and those of reflexive
consciousness or narrative consciousness may differ from both. However,
by building up detailed theories of each type, we may hope to find
important links between them and perhaps even to discover that they
coincide in at least some key respects.


### 4.1 First-person and third-person data




The general descriptive project will require a variety of
investigational methods (Flanagan 1992). Though one might naively
regard the facts of consciousness as too self-evident to require any
systematic methods of gathering data, the epistemic task is in reality
far from trivial (Husserl 1913).




First-person introspective access provides a rich and essential
source of insight into our conscious mental life, but it is neither
sufficient in itself nor even especially helpful unless used in a
trained and disciplined way. Gathering the needed evidence about the
structure of experience requires us both to become phenomenologically
sophisticated self-observers and to complement our introspective
results with many types of third-person data available to external
observers (Searle 1992, Varela 1995, Siewert 1998)




As phenomenologists have known for more than a century, discovering
the structure of conscious experience demands a rigorous inner-directed
stance that is quite unlike our everyday form of self-awareness
(Husserl 1929, Merleau-Ponty 1945). Skilled observation of the needed
sort requires training, effort and the ability to adopt alternative
perspectives on one's experience.




The need for third-person empirical data gathered by external
observers is perhaps most obvious with regard to the more clearly
functional types of consciousness such as access consciousness, but it
is required even with regard to phenomenal and qualitative
consciousness. For example, deficit studies that correlate various
neural and functional sites of damage with abnormalities of conscious
experience can make us aware of aspects of phenomenal structure that
escape our normal introspective awareness. As such case studies show,
things can come apart in experience that seem inseparably unified or
singular from our normal first-person point of view (Sacks 1985,
Shallice 1988, Farah 1995).




Or to pick another example, third-person data can make us aware of
how our experiences of acting and our experiences of event-timing
affect each other in ways that we could never discern through mere
introspection (Libet 1985, Wegner 2002). Nor are the facts gathered by
these third person methods merely about the causes or bases of
consciousness; they often concern the very structure of phenomenal
consciousness itself. First-person, third-person and perhaps even
second-person (Varela 1995) interactive methods will all be needed to
collect the requisite evidence.




Using all these sources of data, we will hopefully be able to
construct detailed descriptive models of the various sorts of
consciousness. Though the specific features of most importance may vary
among the different types, our overall descriptive project will need to
address at least the following seven general aspects of consciousness
(sections 4.2-4.7).


### 4.2 Qualitative character



*Qualitative character* is often equated with so called
"raw feels" and illustrated by the redness one experiences
when one looks at ripe tomatoes or the specific sweet savor one
encounters when one tastes an equally ripe pineapple (Locke 1688). The
relevant sort of qualitative character is not restricted to sensory
states, but is typically taken to be present as an aspect of
experiential states in general, such as experienced thoughts or desires
(Siewert 1998).




The existence of such feels may seem to some to mark the threshold
for states or creatures that are really conscious. If an organism
senses and responds in apt ways to its world but lacks such qualia,
then it might count as conscious at best in a loose and less than
literal sense. Or so at least it would seem to those who take
qualitative consciousness in the "what it is like" sense to
be philosophically and scientifically central (Nagel 1974, Chalmers
1996).




Qualia problems in many forms--Can there be inverted qualia?
(Block 1980a 1980b, Shoemaker 1981, 1982) Are qualia epiphenomenal?
(Jackson 1982, Chalmers 1996) How could neural states give rise to
qualia? (Levine 1983, McGinn 1991)--have loomed large in the
recent past. But the What question raises a more basic problem of
qualia: namely that of giving a clear and articulated description of
our qualia space and the status of specific qualia within it.




Absent such a model, factual or descriptive errors are all too
likely. For example, claims about the unintelligibility of the link
between experienced red and any possible neural substrate of such an
experience sometimes treat the relevant color quale as a simple and
*sui generis* property (Levine 1983), but phenomenal redness in
fact exists within a complex color space with multiple systematic
dimensions and similarity relations (Hardin 1992). Understanding the
specific color quale relative to that larger relational structure not
only gives us a better descriptive grasp of its qualitative nature, it
may also provide some "hooks" to which one might attach
intelligible psycho-physical links.




Color may be the exception in terms of our having a specific and
well developed formal understanding of the relevant qualitative space,
but it is not likely an exception with regard to the importance of such
spaces to our understanding of qualitative properties in general (Clark
1993, P.M. Churchland 1995). (See the entry on
 qualia.)


### 4.3 Phenomenal structure



*Phenomenal structure* should not be conflated with
qualitative structure, despite the sometimes interchangeable use of
"qualia" and "phenomenal properties" in the
literature. "Phenomenal organization" covers all the
various kinds of order and structure found within the domain of
experience, i.e., within the domain of the world as it *appears*
to us. There are obviously important links between the phenomenal and
the qualitative. Indeed qualia might be best understood as properties
of phenomenal or experienced objects, but there is in fact far more to
the phenomenal than raw feels. As Kant (1787), Husserl (1913), and
generations of phenomenologists have shown, the phenomenal structure of
experience is richly intentional and involves not only sensory ideas
and qualities but complex representations of time, space, cause, body,
self, world and the organized structure of lived reality in all its
conceptual and nonconceptual forms.




Since many non-conscious states also have intentional and
representational aspects, it may be best to consider phenomenal
structure as involving a special kind of intentional and
representational organization and content, the kind distinctively
associated with consciousness (Siewert 1998). (See the entry on
 representational theories of consciousness.)




Answering the What question requires a careful account of the
coherent and densely organized representational framework within which
particular experiences are embedded. Since most of that structure is
only implicit in the organization of experience, it can not just be
read off by introspection. Articulating the structure of the phenomenal
domain in a clear and intelligible way is a long and difficult process
of inference and model building (Husserl 1929). Introspection can aid
it, but a lot of theory construction and ingenuity are also needed.



There has been recent philosophical debate about the range of
properties that are phenomenally present or manifest in conscious
experience, in particular with respect to cognitive states such as
believing or thinking. Some have argued for a so called
"thin" view according to which phenomenal properties are
limited to qualia representing basic sensory properties, such as
colors, shapes, tones and feels. According to such theorists, there
is no distinctive "what-it-is-likeness" involved in
believing that Paris is the capital of France or that 17 is a prime
number (Tye, Prinz 2012). Some imagery, e.g., of the Eiffel Tower, may
accompany our having such a thought, but that is incidental to it
and the cognitive state itself has no phenomenal feel. On the thin
view, the phenomenal aspect of perceptual states as well is limited to
basic sensory features; when one sees an image of Winston Churchill,
one's perceptual phenomenology is limited only to the spatial aspects
of his face.




Others holds a "thick" view according to which the
phenomenology of perception includes a much wider range of features
and cognitive states have a distinctive phenomenology as well
(Strawson 2003, Pitt 2004, Seigel 2010). On the thick view, the
what-it-is-likeness of perceiving an image of Marilyn Monroe includes
one's recognition of her history as part of the felt aspect of the
experience, and beliefs and thoughts as well can and typically do have
a distinctive nonsensory phenomenology. Both sides of the debate are
well represented in the volume Cognitive Phenomenology (Bayne and
Montague 2010). 


### 4.4 Subjectivity



*Subjectivity* is another notion sometimes equated with the
qualitative or the phenomenal aspects of consciousness in the
literature, but again there are good reason to recognize it, at least
in some of its forms, as a distinct feature of
consciousness--related to the qualitative and the phenomenal but
different from each. In particular, the epistemic form of
subjectivity concerns apparent limits on the knowability or even the
understandability of various facts about conscious experience (Nagel
1974, Van Gulick 1985, Lycan 1996).




On Thomas Nagel's (1974) account, facts about what it is like to be
a bat are subjective in the relevant sense because they can be fully
understood only from the bat-type point of view. Only creatures capable
of having or undergoing similar such experiences can understand their
what-it's-likeness in the requisite empathetic sense. Facts about
conscious experience can be at best incompletely understood from an
outside third person point of view, such as those associated with
objective physical science. A similar view about the limits of
third-person theory seems to lie behind claims regarding what Frank
Jackson's (1982) hypothetical Mary, the super color scientist, could
not understand about experiencing red because of her own impoverished
history of achromatic visual experience.




Whether facts about experience are indeed epistemically limited in
this way is open to debate (Lycan 1996), but the claim that
understanding consciousness requires special forms of knowing and
access from the inside point of view is intuitively plausible and has a
long history (Locke 1688). Thus any adequate answer to the What
question must address the epistemic status of consciousness, both our
abilities to understand it and their limits (Papineau 2002, Chalmers
2003). (See the entry on 
 self-knowledge.)


### 4.5 Self-perspectival organization




The perspectival structure of consciousness is one aspect of its
overall phenomenal organization, but it is important enough to merit
discussion in its own right. Insofar as the key perspective is that of
the conscious self, the specific feature might be called
*self-perspectuality.* Conscious experiences do not exist as
isolated mental atoms, but as modes or states of a conscious self or
subject (Descartes 1644, Searle 1992, though pace Hume 1739). A visual
experience of a blue sphere is always a matter of there being some self
or subject who is appeared to in that way. A sharp and stabbing pain is
always a pain felt or experienced by some conscious subject. The self
need not appear as an explicit element in our experiences, but as Kant
(1787) noted the "I think" must at least potentially
accompany each of them.




The self might be taken as the perspectival point from which the
world of objects is present to experience (Wittgenstein 1921). It
provides not only a spatial and temporal perspective for our experience
of the world but one of meaning and intelligibility as well. The
intentional coherence of the experiential domain relies upon the dual
interdependence between self and world: the self as perspective from
which objects are known and the world as the integrated structure of
objects and events whose possibilities of being experienced implicitly
define the nature and location of the self (Kant 1787, Husserl
1929).




Conscious organisms obviously differ in the extent to which they
constitute a unified and coherent self, and they likely differ
accordingly in the sort or degree of perspectival focus they embody in
their respective forms of experience (Lorenz 1977). Consciousness may
not require a distinct or substantial self of the traditional Cartesian
sort, but at least some degree of perspectivally self-like organization
seems essential for the existence of anything that might count as
conscious experience. Experiences seem no more able to exist without a
self or subject to undergo them than could ocean waves exist without
the sea through which they move. The Descriptive question thus requires
some account of the self-perspectival aspect of experience and the
self-like organization of conscious minds on which it depends, even if
the relevant account treats the self in a relatively deflationary and
virtual way (Dennett 1991, 1992).


### 4.6 Unity



*Unity* is closely linked with the self-perspective, but it
merits specific mention on its own as a key aspect of the organization
of consciousness. Conscious systems and conscious mental states both
involve many diverse forms of unity. Some are causal unities associated
with the integration of action and control into a unified focus of
agency. Others are more representational and intentional forms of unity
involving the integration of diverse items of content at many scales
and levels of binding (Cleeremans 2003).




Some such integrations are relatively local as when diverse features
detected within a single sense modality are combined into a
representation of external objects bearing those features, e.g. when
one has a conscious visual experience of a moving red soup can passing
above a green striped napkin (Triesman and Gelade 1980).




Other forms of intentional unity encompass a far wider range of
contents. The content of one's present experience of the room in which
one sits depends in part upon its location within a far larger
structure associated with one's awareness of one's existence as an
ongoing temporally extended observer within a world of spatially
connected independently existing objects (Kant 1787, Husserl 1913). The
individual experience can have the content that it does only because it
resides within that larger unified structure of representation. (See
the entry on
 unity of consciousness.)



Particular attention has been paid recently to the notion of
phenomenal unity (Bayne 2010) and its relation to other forms of
conscious unity such as those involving representational, functional
or neural integration. Some have argued that phenomenal unity can be
reduced to representational unity (Tye 2005) while others have denied
the possibility of any such reduction (Bayne 2010).


### 4.7 Intentionality and transparency




Conscious mental states are typically regarded as having a
representational or intentional aspect in so far as they are about
things, refer to things or have satisfaction conditions. One's
conscious visual experience *correctly represent*s the world if
there are lilacs in a white vase on the table (pace Travis 2004), one's
conscious memory is *of* the attack on the World Trade Center,
and one's conscious desire is *for* a glass of cold water.
However, nonconscious states can also exhibit intentionality in such
ways, and it is important to understand the ways in which the
representational aspects of conscious states resemble and differ from
those of nonconscious states (Carruthers 2000). Searle (1990) offers a
contrary view according to which only conscious states and dispositions
to have conscious states can be genuinely intentional, but most
theorists regard intentionality as extending widely into the
unconscious domain. (See the entry on
 consciousness and intentionality.)




One potentially important dimension of difference concerns so called
*transparency*, which is an important feature of consciousness
in two interrelated metaphoric senses, each of which has an
intentional, an experiential and a functional aspect.




Conscious perceptual experience is often said to be transparent, or
in G.E. Moore's (1922) phrase "diaphanous". We
transparently "look through" our sensory experience in so
far as we seem directly aware of external objects and events present to
us rather than being aware of any properties of experience by which it
presents or represents such objects to us. When I look out at the
wind-blown meadow, it is the undulating green grass of which I am aware
not of any green property of my visual experience. (See the entry on
 representational theories of consciousness.)
 Moore himself believed we could become aware of those latter
qualities with effort and redirection of attention, though some
contemporary transparency advocates deny it (Harman 1990, Tye
1995, Kind 2003).




Conscious thoughts and experiences are also transparent in a
semantic sense in that their meanings seem immediately known to us in
the very act of thinking them (Van Gulick 1992). In that sense we might
be said to 'think right through' them to what they mean or
represent. Transparency in this semantic sense may correspond at least
partly with what John Searle calls the "intrinsic
intentionality" of consciousness (Searle 1992).




Our conscious mental states seem to have their meanings
intrinsically or from the inside just by being what they are in
themselves, by contrast with many externalist theories of mental
content that ground meaning in causal, counterfactual or informational
relations between bearers of intentionality and their semantic or
referential objects.




The view of conscious content as intrinsically determined and
internally self-evident is sometimes supported by appeals to brain in
the vat intuitions, which make it seem that the envatted brain's
conscious mental states would keep all their normal intentional
contents despite the loss of all their normal causal and informational
links to the world (Horgan and Tienson 2002). There is continued
controversy about such cases and about competing internalist (Searle
1992) and externalist views (Dretske 1995) of conscious
intentionality.




Though semantic transparency and intrinsic intentionality have some
affinities, they should not be simply equated, since it may be possible
to accommodate the former notion within a more externalist account of
content and meaning. Both semantic and sensory transparency obviously
concern the representational or intentional aspects of consciousness,
but they are also experiential aspects of our conscious life. They are
part of what it's like or how it feels phenomenally to be conscious.
They also both have functional aspects, in so far as conscious experiences
interact with each other in richly content-appropriate ways that
manifest our transparent understanding of their contents.


### 4.8 Dynamic flow




The *dynamics* of consciousness are evident in the coherent
order of its ever changing process of flow and self-transformation,
what William James (1890) called the *"stream of
consciousness*." Some temporal sequences of experience are
generated by purely internal factors as when one thinks through a
puzzle, and others depend in part upon external causes as when one
chases a fly ball, but even the latter sequences are shaped in large
part by how consciousness transforms itself.




Whether partly in response to outer influences or entirely from
within, each moment to moment sequence of experience grows coherently
out of those that preceded it, constrained and enabled by the global
structure of links and limits embodied in its underlying prior
organization (Husserl 1913). In that respect, consciousness is an
autopoietic system, i.e., a self-creating and self-organizing system
(Varela and Maturana 1980).




As a conscious mental agent I can do many things such as scan my
room, scan a mental image of it, review in memory the courses of a
recent restaurant meal along with many of its tastes and scents, reason
my way through a complex problem, or plan a grocery shopping trip and
execute that plan when I arrive at the market. These are all routine
and common activities, but each involves the directed generation of
experiences in ways that manifest an implicit practical understanding
of their intentional properties and interconnected contents (Van Gulick
2000).




Consciousness is a dynamic process, and thus an adequate descriptive
answer to the What question must deal with more than just its static or
momentary properties. In particular, it must give some account of the
temporal dynamics of consciousness and the ways in which its
self-transforming flow reflects both its intentional coherence and the
semantic self-understanding embodied in the organized controls through
which conscious minds continually remake themselves as autopoietic
systems engaged with their worlds.




A comprehensive descriptive account of consciousness would need to
deal with more than just these seven features, but having a clear
account of each of them would take us a long way toward answering the
"What is consciousness?" question.


## 5. The explanatory question: *How* can consciousness exist?




The *How* question focuses on explanation rather than
description. It asks us to explain the basic status of consciousness
and its place in nature. Is it a fundamental feature of reality in its
own right, or does its existence depend upon other nonconscious items,
be they physical, biological, neural or computational? And if the
latter, can we explain or understand how the relevant nonconscious
items could cause or realize consciousness? Put simply, can we explain
how to make something conscious out of things that are not
conscious?


### 5.1 Diversity of explanatory projects




The How question is not a single question, but rather a general
family of more specific questions (Van Gulick 1995). They all concern
the possibility of explaining some sort or aspect of consciousness, but
they vary in their particular explananda, the restrictions on their
explanans, and their criteria for successful explanation. For example,
one might ask whether we can explain access consciousness
computationally by mimicking the requisite access relations in a
computational model. Or one might be concerned instead with whether the
phenomenal and qualitative properties of a conscious creature's mind
can be *a priori* deduced from a description of the neural
properties of its brain processes. Both are versions of the How
question, but they ask about the prospects of very different
explanatory projects, and thus may differ in their answers (Lycan
1996). It would be impractical, if not impossible, to catalog all the
possible versions of the How question, but some of the main options can be
listed.



*Explananda.* Possible explananda would include the various
sorts of state and creature consciousness distinguished above, as well
as the seven features of consciousness listed in response to the What
question. Those two types of explananda overlap and intersect. We might
for example aim to explain the dynamic aspect either of phenomenal or
of access consciousness. Or we could try to explain the subjectivity of
either qualitative or meta-mental consciousness. Not every feature
applies to every sort of consciousness, but all apply to several. How
one explains a given feature in relation to one sort of consciousness
may not correspond with what is needed to explain it relative to
another.



*Explanans.* The range of possible explanans is also diverse.
In perhaps its broadest form, the How question asks how consciousness
of the relevant sort could be caused or realized by nonconscious items,
but we can generate a wealth of more specific questions by further
restricting the range of the relevant explanans. One might seek to
explain how a given feature of consciousness is caused or realized by
underlying *neural* processes, *biological* structures,
*physical* mechanisms, *functional* or
*teleofunctional* relations, *computational*
organization, or even by *nonconscious mental* states. The
prospects for explanatory success will vary accordingly. In general the
more limited and elementary the range of the explanans, the more
difficult the problem of explaining how could it suffice to produce
consciousness (Van Gulick 1995).



*Criteria of explanation.* The third key parameter is how one
defines the criterion for a successful explanation. One might require
that the explanandum be *a priori* deducible from the explanans,
although it is controversial whether this is either a necessary or a
sufficient criterion for explaining consciousness (Jackson 1993). Its
sufficiency will depend in part on the nature of the premises from
which the deduction proceeds. As a matter of logic, one will need some
bridge principles to connect propositions or sentences about
consciousness with those that do not mention it. If one's premises
concern physical or neural facts, then one will need some bridge
principles or links that connect such facts with facts about
consciousness (Kim 1998). Brute links, whether nomic or merely well
confirmed correlations, could provide a logically sufficient bridge to
infer conclusions about consciousness. But they would probably not
allow us to see how or why those connections hold, and thus they would
fall short of fully explaining how consciousness exists (Levine 1983,
1993, McGinn 1991).




One could legitimately ask for more, in particular for some account
that made intelligible why those links hold and perhaps why they could
not fail to do so. A familiar two-stage model for explaining
macro-properties in terms of micro-substrates is often invoked. In the
first step, one analyzes the macro-property in terms of functional
conditions, and then in the second stage one shows that the
micro-structures obeying the laws of their own level nomically suffice
to guarantee the satisfaction of the relevant functional conditions
(Armstrong 1968, Lewis 1972).




The micro-properties of collections of H2O molecules at 20degC
suffice to satisfy the conditions for the liquidity of the water they
compose. Moreover, the model makes intelligible how the liquidity is
produced by the micro-properties. A satisfactory explanation of how
consciousness is produced might seem to require a similar two stage
story. Without it, even *a priori* deducibility might seem
explanatorily less than sufficient, though the need for such a story
remains a matter of controversy (Block and Stalnaker 1999, Chalmers
and Jackson 2001).


### 5.2 The explanatory gap




Our current inability to supply a suitably intelligible link is
sometimes described, following Joseph Levine (1983), as the existence
of an *explanatory gap*, and as indicating our incomplete
understanding of how consciousness might depend upon a nonconscious
substrate, especially a physical substrate. The basic gap claim admits
of many variations in generality and thus in strength.




In perhaps its weakest form, it asserts a *practical* limit
on our *present* explanatory abilities; given our current
theories and models we can not now articulate an intelligible link. A
stronger version makes an *in principle* claim about our
*human capacities* and thus asserts that given our human
cognitive limits we will never be able to bridge the gap. To us, or
creatures cognitively like us, it must remain a residual mystery
(McGinn 1991). Colin McGinn (1995) has argued that given the inherently
spatial nature of both our human perceptual concepts and the scientific
concepts we derive from them, we humans are not conceptually suited for
understanding the nature of the psychophysical link. Facts about that
link are as cognitively closed to us as are facts about multiplication
or square roots to armadillos. They do not fall within our conceptual
and cognitive repertoire. An even stronger version of the gap claim
removes the restriction to our cognitive nature and denies *in
principle* that the gap can be closed by *any cognitive
agents*.




Those who assert gap claims disagree among themselves about what
metaphysical conclusions, if any, follow from our supposed epistemic
limits. Levine himself has been reluctant to draw any anti-physicalist
ontological conclusions (Levine 1993, 2001). On the other hand some
neodualists have tried to use the existence of the gap to refute
physicalism (Foster 1996, Chalmers 1996). The stronger one's
epistemological premise, the better the hope of deriving a metaphysical
conclusion. Thus unsurprisingly, dualist conclusions are often
supported by appeals to the supposed impossibility *in
principle* of closing the gap.




If one could see on *a priori* grounds that there is no way
in which consciousness could be intelligibly explained as arising from
the physical, it would not be a big step to concluding that it in fact
does not do so (Chalmers 1996). However, the very strength of such an
epistemological claim makes it difficult to assume with begging the
metaphysical result in question. Thus those who wish to use a strong
*in principle* gap claim to refute physicalism must find
independent grounds to support it. Some have appealed to conceivability
arguments for support, such as the alleged conceivability of zombies
molecularly identical with conscious humans but devoid of all
phenomenal consciousness (Campbell 1970, Kirk 1974, Chalmers 1996).
Other supporting arguments invoke the supposed non-functional nature of
consciousness and thus its alleged resistance to the standard
scientific method of explaining complex properties (e.g., genetic
dominance) in terms of physically realized functional conditions (Block
1980a, Chalmers 1996). Such arguments avoid begging the
anti-physicalist question, but they themselves rely upon claims and
intuitions that are controversial and not completely independent of
one's basic view about physicalism. Discussion on the topic remains
active and ongoing.




Our present inability to see any way of closing the gap may exert
some pull on our intuitions, but it may simply reflect the limits of
our current theorizing rather than an unbridgeable in principle barrier
(Dennett 1991). Moreover, some physicalists have argued that
explanatory gaps are to be expected and are even entailed by plausible
versions of ontological physicalism, ones that treat human agents as
physically realized cognitive systems with inherent limits that derive
from their evolutionary origin and situated contextual mode of
understanding (Van Gulick 1985, 2003; McGinn 1991, Papineau 1995,
2002). On this view, rather than refuting physicalism, the existence of
explanatory gaps may confirm it. Discussion and disagreement on these
topics remains active and ongoing.


### 5.3 Reductive and non-reductive explanation




As the need for intelligible linkage has shown, *a priori*
deducibility is not in itself obviously sufficient for successful
explanation (Kim 1980), nor is it clearly necessary. Some weaker
logical link might suffice in many explanatory contexts. We can
sometimes tell enough of a story about how facts of one sort depend
upon those of another to satisfy ourselves that the latter do in fact
cause or realize the former even if we can not strictly deduce all the
former facts from the latter.




Strict intertheoretical deduction was taken as the reductive norm by
the logical empiricist account of the unity of science (Putnam and
Oppenheim 1958), but in more recent decades a looser nonreductive
picture of relations among the various sciences has gained favor. In
particular, nonreductive materialists have argued for the so called
"autonomy of the special sciences" (Fodor 1974) and for the
view that understanding the natural world requires us to use a
diversity of conceptual and representational systems that may not be
strictly intertranslatable or capable of being put into the tight
correspondence required by the older deductive paradigm of interlevel
relations (Putnam 1975).




Economics is often cited as an example (Fodor 1974, Searle 1992).
Economic facts may be realized by underlying physical processes, but no
one seriously demands that we be able to deduce the relevant economic
facts from detailed descriptions of their underlying physical bases or
that we be able to put the concepts and vocabulary of economics in
tight correspondence with those of the physical sciences.




Nonetheless our deductive inability is not seen as cause for
ontological misgivings; there is no "money-matter" problem.
All that we require is some general and less than deductive
understanding of how economic properties and relations might be
underlain by physical ones. Thus one might opt for a similar criterion
for interpreting the How question and for what counts as explaining how
consciousness might be caused or realized by nonconscious items.
However, some critics, such as Kim (1987), have challenged the
coherence of any view that aims to be both non-reductive and
physicalist, though supporters of such views have replied in turn (Van
Gulick 1993).




Others have argued that consciousness is especially resistant to
explanation in physical terms because of the inherent differences
between our subjective and objective modes of understanding. Thomas
Nagel famously argued (1974) that there are unavoidable limits placed on our
ability to understand the phenomenology of bat experience by our
inability to empathetically take on an experiential perspective like
that which characterizes the bat's echo-locatory auditory experience of
its world. Given our inability to undergo similar experience, we can
have at best partial understanding of the nature of such experience. No
amount of knowledge gleaned from the external objective third-person
perspective of the natural sciences will supposedly suffice to allow us
to understand what the bat can understand of its own experience from
its internal first-person subjective point of view.


### 5.4 Prospects of explanatory success




The How question thus subdivides into a diverse family of more
specific questions depending upon the specific sort or feature of
consciousness one aims to explain, the specific restrictions one places
on the range of the explanans and the criterion one uses to define
explanatory success. Some of the resulting variants seem easier to
answer than others. Progress may seem likely on some of the so called
"easy problems" of consciousness, such as explaining the
dynamics of access consciousness in terms of the functional or
computational organization of the brain (Baars 1988). Others may seem
less tractable, especially the so-called "hard problem"
(Chalmers 1995) which is more or less that of giving an intelligible
account that lets us see in an intuitively satisfying way how
phenomenal or "what it's like" consciousness might arise
from physical or neural processes in the brain.




Positive answers to some versions of the How questions seem near at
hand, but others appear to remain deeply baffling. Nor should we assume
that every version has a positive answer. If dualism is true, then
consciousness in at least some of its types may be basic and
fundamental. If so,we will not be able to explain how it arises from
nonconscious items since it simply does not do so.




One's view of the prospects for explaining consciousness will
typically depend upon one's perspective. Optimistic physicalists will
likely see current explanatory lapses as merely the reflection of the
early stage of inquiry and sure to be remedied in the not too distant
future (Dennett 1991, Searle 1992, P. M.Churchland 1995). To dualists,
those same impasses will signify the bankruptcy of the physicalist
program and the need to recognize consciousness as a fundamental
constituent of reality in its own right (Robinson 1982, Foster 1989,
1996, Chalmers 1996). What one sees depends in part on where one
stands, and the ongoing project of explaining consciousness will be
accompanied by continuing debate about its status and prospects for
success.


## 6. The functional question: *Why* does consciousness exist?




The functional or *Why* question asks about the
*value* or *role* or consciousness and thus indirectly
about its origin. Does it have a *function*, and if so what
is it? Does it make a difference to the operation of systems in which
it is present, and if so why and how? If consciousness exists as a
complex feature of biological systems, then its adaptive value is
likely relevant to explaining its evolutionary origin, though of course
its present function, if it has one, need not be the same as that it
may have had when it first arose. Adaptive functions often change over
biological time. Questions about the value of consciousness also have a
*moral* dimension in at least two ways. We are inclined to
regard an organism's moral status as at least partly determined by the
nature and extent to which it is conscious, and conscious states,
especially conscious affective states such as pleasures and pains, play
a major role in many of the accounts of value that underlie moral
theory (Singer 1975).




As with the What and How questions, the Why question poses a general
problem that subdivides into a diversity of more specific inquiries. In
so far as the various sorts of consciousness, e.g., access, phenomenal,
meta-mental, are distinct and separable--which remains an open
question--they likely also differ in their specific roles and
values. Thus the Why question may well not have a single or uniform
answer.


### 6.1 Causal status of consciousness




Perhaps the most basic issue posed by any version of the Why
question is whether or not consciousness of the relevant sort has any
causal impact at all. If it has no effects and makes no causal
difference whatsoever, then it would seem unable to play any
significant role in the systems or organisms in which it is present,
thus undercutting at the outset most inquiries about its possible
value. Nor can the threat of epiphenomenal irrelevance be simply
dismissed as an obvious non-option, since at least some forms of
consciousness have been seriously alleged in the recent literature to
lack causal status. (See the entry on
 epiphenomenalism.)
 Such worries have been raised especially with regard to qualia and
qualitative consciousness (Huxley 1874, Jackson 1982, Chalmers 1996),
but challenges have also been leveled against the causal status of
other sorts including meta-mental consciousness (Velmans 1991).




Both metaphysical and empirical arguments have been given in support
of such claims. Among the former are those that appeal to intuitions
about the conceivability and logical possibility of zombies, i.e., of
beings whose behavior, functional organization, and physical structure
down to the molecular level are identical to those of normal human
agents but who lack any qualia or qualitative consciousness. Some (Kirk
1970, Chalmers 1996) assert such beings are possible in worlds that
share all our physical laws, but others deny it (Dennett 1991, Levine
2001). If they are possible in such worlds, then it would seem to
follow that even in our world, qualia do not affect the course of
physical events including those that constitute our human behaviors. If
those events unfold in the same way whether or not qualia are present,
then qualia appear to be inert or epiphenomenal at least with respect
to events in the physical world. However, such arguments and the zombie
intuitions on which they rely are controversial and their soundness
remains in dispute (Searle 1992, Yablo 1998, Balog 1999).




Arguments of a far more empirical sort have challenged the causal
status of meta-mental consciousness, at least in so far as its presence
can be measured by the ability to report on one's mental state.
Scientific evidence is claimed to show that consciousness of that sort
is neither necessary for any type of mental ability nor does it occur
early enough to act as a cause of the acts or processes typically
thought to be its effects (Velmans 1991). According to those who make
such arguments, the sorts of mental abilities that are typically
thought to require consciousness can all be realized unconsciously in
the absence of the supposedly required self-awareness.




Moreover, even when conscious self-awareness is present, it
allegedly occurs too late to be the cause of the relevant actions
rather than their result or at best a joint effect of some shared prior
cause (Libet 1985). Self-awareness or meta-mental consciousness
according to these arguments turns out to be a psychological
after-effect rather than an initiating cause, more like a *post
facto* printout or the result displayed on one's computer screen
than like the actual processor operations that produce both the
computer's response and its display.




Once again the arguments are controversial, and both the supposed
data and their interpretation are subjects of lively disagreement (see
Flanagan 1992, and commentaries accompanying Velmans 1991). Though the
empirical arguments, like the zombie claims, require one to consider
seriously whether some forms of consciousness may be less causally
potent than is typically assumed, many theorists regard the empirical
data as no real threat to the causal status of consciousness.




If the epiphenomenalists are wrong and consciousness, in its various
forms, is indeed causal, what sorts of effects does it have and what
differences does it make? How do mental processes that involve the
relevant sort of consciousness differ form those that lack it? What
function(s) might consciousness play? The following six sections
(6.2-6.7) discuss some of the more commonly given
answers. Though the various functions overlap to some degree, each is
distinct, and they differ as well in the sorts of consciousness with
which each is most aptly linked.


### 6.2 Flexible control



*Increased flexibility and sophistication of control.*
Conscious mental processes appear to provide highly flexible and
adaptive forms of control. Though unconscious automatic processes can
be extremely efficient and rapid, they typically operate in ways that
are more fixed and predetermined than those which involve conscious
self-awareness (Anderson 1983). Conscious awareness is thus of most
importance when one is dealing with novel situations and previously
unencountered problems or demands (Penfield 1975, Armstrong 1981).




Standard accounts of skill acquisition stress the importance of
conscious awareness during the initial learning phase, which gradually
gives way to more automatic processes of the sort that require little
attention or conscious oversight (Schneider and Shiffrin 1977).
Conscious processing allows for the construction or compilation of
specifically tailored routines out of elementary units as well as for
the deliberate control of their execution.




There is a familiar tradeoff between flexibility and speed;
controlled conscious processes purchase their customized versatility at
the price of being slow and effortful in contrast to the fluid rapidity
of automatic unconscious mental operations (Anderson 1983). The
relevant increases in flexibility would seem most closely connected
with the meta-mental or higher-order form of consciousness in so far as
the enhanced ability to control processes depends upon greater
self-awareness. However, flexibility and sophisticated modes of control
may be associated as well with the phenomenal and access forms of
consciousness.


### 6.3 Social coordination



*Enhanced capacity for social coordination.* Consciousness of
the meta-mental sort may well involve not only an increase in
self-awareness but also an enhanced understanding of the mental states
of other minded creatures, especially those of other members of one's
social group (Humphreys 1982). Creatures that are conscious in the
relevant meta-mental sense not only have beliefs, motives, perceptions
and intentions but understand what it is to have such states and are
aware of both themselves and others as having them.




This increase in mutually shared knowledge of each other's minds,
enables the relevant organisms to interact, cooperate and communicate
in more advanced and adaptive ways. Although meta-mental consciousness
is the sort most obviously linked to such a socially coordinative role,
narrative consciousness of the kind associated with the stream of
consciousness is also clearly relevant in so far as it involves the
application to one's own case of the interpretative abilities that
derive in part from their social application (Ryle 1949, Dennett 1978,
1992).


### 6.4 Integrated representation



*More unified and densely integrated representation of
reality*. Conscious experience presents us with a world of objects
independently existing in space and time. Those objects are typically
present to us in a multi-modal fashion that involves the integration of
information from various sensory channels as well as from background
knowledge and memory. Conscious experience presents us not with
isolated properties or features but with objects and events situated in
an ongoing independent world, and it does so by embodying in its
experiential organization and dynamics the dense network of relations
and interconnections that collectively constitute the meaningful
structure of a world of objects (Kant 1787, Husserl 1913, Campbell
1997).




Of course, not all sensory information need be experienced to have
an adaptive effect on behavior. Adaptive non-experiential sensory-motor
links can be found both in simple organisms, as well as in some of the
more direct and reflexive processes of higher organisms. But when
experience is present, it provides a more unified and integrated
representation of reality, one that typically allows for more
open-ended avenues of response (Lorenz 1977). Consider for example the
representation of space in an organism whose sensory input channels are
simply linked to movement or to the orientation of a few fixed
mechanisms such as those for feeding or grabbing prey, and compare it
with that in an organism capable of using its spatial information for
flexible navigation of its environment and for whatever other spatially
relevant aims or goals it may have, as when a person visually scans her
office or her kitchen (Gallistel 1990).




It is representation of this latter sort that is typically made
available by the integrated mode of presentation associated with
conscious experience. The unity of experienced space is just one
example of the sort of integration associated with our conscious
awareness of an objective world. (See the entry on
 unity of consciousness.)



This integrative role or value is most directly associated with access
consciousness, but also clearly with the larger phenomenal and
intentional structure of experience. It is relevant even to the
qualitative aspect of consciousness in so far as qualia play an
important role in our experience of unified objects in a unified space
or scene. It is intimately tied as well to the transparency of
experience described in response to the What question, especially to
semantic transparency (Van Gulick 1993). Integration of information
plays a major role in several current neuro-cognitive theories of
consciousness especially Global Workspace theories (see section 9.5)
and Giulio Tononi's Integrated Information theory (section 9.6
below).


### 6.5 Informational access



*More global informational access*. The information carried
in conscious mental states is typically available for use by a
diversity of mental subsystems and for application to a wide range of
potential situations and actions (Baars 1988). Nonconscious information
is more likely to be encapsulated within particular mental modules and
available for use only with respect to the applications directly
connected to that subsystem's operation (Fodor 1983). Making
information conscious typically widens the sphere of its influence and
the range of ways it which it can be used to adaptively guide or shape
both inner and outer behavior. A state's being conscious may be in part
a matter of what Dennett calls "cerebral celebrity", i.e.,
of its ability to have a content-appropriate impact on other mental
states.



This particular role is most directly and definitionally tied to the
notion of access consciousness (Block 1995), but meta-mental
consciousness as well as the phenomenal and qualitative forms all seem
plausibly linked to such increases in the availability of information
(Armstrong 1981, Tye 1985). Diverse cognitive and neuro-cognitive
theories incorporate access as a central feature of consciousness and
conscious processing. Global Workspace theories, Prinz's Attendend
Intermediate Representation (AIR) (Prinz 2012) and Tononi's Integrated
Information Theory (IIT) all distinguish conscious states and
processes at least partly in terms of enhanced wide spread access to
the state's content (see section 9.6).




### 6.6 Freedom of will



*Increased freedom of choice or free will*. The issue of free
will remains a perennial philosophical problem, not only with regard to
whether or not it exists but even as to what it might or should consist
in (Dennett 1984, van Inwagen 1983, Hasker 1999, Wegner 2002). (See
the entry on
 free will.)
 The notion of free will may itself remain too murky and contentious
to shed any clear light on the role of consciousness, but there is a
traditional intuition that the two are deeply linked.




Consciousness has been thought to open a realm of possibilities, a
sphere of options within which the conscious self might choose or act
freely. At a minimum, consciousness might seem a necessary precondition
for any such freedom or self-determination (Hasker 1999). How could one
engage in the requisite sort of free choice, while remaining solely
within the unconscious domain? How can one determine one's own will
without being conscious of it and of the options one has to shape
it.




The freedom to chose one's actions and the ability to determine
one's own nature and future development may admit of many interesting
variations and degrees rather than being a simple all or nothing matter,
and various forms or levels of consciousness might be correlated with
corresponding degrees or types of freedom and self-determination
(Dennett 1984, 2003). The link with freedom seems strongest for the
meta-mental form of consciousness given its emphasis on self-awareness,
but potential connections also seem possible for most of the other
sorts as well.


### 6.7 Intrinsic motivation



*Intrinsically motivating states*. At least some conscious
states appear to have the motive force they do intrinsically. In
particular, the functional and motivational roles of conscious
affective states, such as pleasures and pains, seem intrinsic to their
experiential character and inseparable from their qualitative and
phenomenal properties, though the view has been challenged (Nelkin
1989, Rosenthal 1991). The attractive positive motivational aspect of a
pleasure seems a part of its directly experienced phenomenal feel, as
does the negative affective character of a pain, at least in the case
of normal non-pathological experience.




There is considerable disagreement about the extent to which the
feel and motive force of pain can dissociate in abnormal cases, and
some have denied the existence of such intrinsically motivating aspects
altogether (Dennett 1991). However, at least in the normal case, the
negative motivational force of pain *seems* built right into the
feel of the experience itself.




Just *how* this might be so remains less than clear, and
perhaps the appearance of intrinsic and directly experienced
motivational force is illusory. But if it is real, then it may be one
of the most important and evolutionarily oldest respects in which
consciousness makes a difference to the mental systems and processes in
which it is present (Humphreys 1992).




Other suggestions have been made about the possible roles and value
of consciousness, and these six surely do not exhaust the options.
Nonetheless, they are among the most prominent recent hypotheses, and
they provide a fair survey of the sorts of answers that have been
offered to the Why question by those who believe consciousness does
indeed make a difference.


### 6.8 Constitutive and contingent roles




One further point requires clarification about the various respects
in which the proposed functions might answer the Why question. In
particular one should distinguish between *constitutive* cases
and cases of *contingent realization*. In the former, fulfilling
the role constitutes being conscious in the relevant sense, while in
the latter case consciousness of a given sort is just one way among
several in which the requisite role might be realized (Van Gulick
1993).




For example, making information globally available for use by a wide
variety of subsystems and behavioral applications may constitute its
being conscious in the access sense. By contrast, even if the
qualitative and phenomenal forms of consciousness involve a highly
unified and densely integrated representation of objective reality, it
may be possible to produce representations having those functional
characteristics but which are not qualitative or phenomenal in
nature.




The fact that *in us* the modes of representation with those
characteristics also have qualitative and phenomenal properties may
reflect contingent historical facts about the particular design
solution that happened to arise in our evolutionary ancestry. If so,
there may be quite other means of achieving a comparable result without
qualitative or phenomenal consciousness. Whether this is the right way
to think about phenomenal and qualitative conscious is unclear; perhaps
the tie to unified and densely integrated representation is in fact as
intimate and constitutive as it seems to be in the case of access
consciousness (Carruthers 2000). Regardless of how that issue gets
resolved, it is important to not to conflate constitution accounts with
contingent realization accounts when addressing the function of
consciousness and answering the question of why it exists (Chalmers
1996).


## 7. Theories of consciousness




In response to the What, How and Why questions many theories of
consciousness have been proposed in recent years. However, not all
theories of consciousness are theories of the same thing. They vary not
only in the specific sorts of consciousness they take as their object,
but also in their theoretical aims.




Perhaps the largest division is between general metaphysical
theories that aim to locate consciousness in the overall ontological
scheme of reality and more specific theories that offer detailed
accounts of its nature, features and role. The line between the two
sorts of theories blurs a bit, especially in so far as many specific
theories carry at least some implicit commitments on the more general
metaphysical issues. Nonetheless, it is useful to keep the division in
mind when surveying the range of current theoretical offerings.


## 8. Metaphysical theories of consciousness




General metaphysical theories offer answers to the conscious version
of the mind-body problem, "What is the ontological status of
consciousness relative to the world of physical reality?" The
available responses largely parallel the standard mind-body options
including the main versions of dualism and physicalism.


### 8.1 Dualist theories



*Dualist theories* regard at least some aspects of
consciousness as falling outside the realm of the physical,but specific
forms of dualism differ in just which aspects those are. (See the entry
 on
 dualism.)



*Substance dualism*, such as traditional Cartesian dualism
(Descartes 1644), asserts the existence of both physical and
non-physical substances. Such theories entail the existence of
non-physical minds or selves as entities in which consciousness
inheres. Though substance dualism is at present largely out of favor,
it does have some contemporary proponents (Swinburne 1986, Foster 1989,
1996).



*Property dualism* in its several versions enjoys a greater
level of current support. All such theories assert the existence of
conscious properties that are neither identical with nor reducible to
physical properties but which may nonetheless be instantiated by the
very same things that instantiate physical properties. In that respect
they might be classified as *dual aspect* theories. They take
some parts of reality--organisms, brains, neural states or
processes--to instantiate properties of two distinct and
disjoint sorts: physical ones and conscious, phenomenal or qualitative
ones. Dual aspect or property dualist theories can be of at least three
different types.



*Fundamental property dualism* regards conscious mental
properties as basic constituents of reality on a par with fundamental
physical properties such as electromagnetic charge. They may interact
in causal and law-like ways with other fundamental properties such as
those of physics, but ontologically their existence is not dependent
upon nor derivative from any other properties (Chalmers 1996).



*Emergent property dualism* treats conscious properties as
arising from complex organizations of physical constituents but as
doing so in a radical way such that the emergent result is something
over and above its physical causes and is not *a priori*
predictable from nor explicable in terms of their strictly physical
natures. The coherence of such emergent views has been challenged (Kim
1998) but they have supporters (Hasker 1999).



*Neutral monist property dualism* treats both conscious
mental properties and physical properties as in some way dependent upon
and derivative from a more basic level of reality, that in itself is
neither mental nor physical (Russell 1927, Strawson 1994). However, if
one takes dualism to be a claim about there being two distinct realms
of fundamental entities or properties, then perhaps neutral monism
should not be classified as a version of property dualism in so far as
it does not regard either mental or physical properties as ultimate or
fundamental.



*Panpsychism* might be regarded as a fourth type of property
dualism in that it regards all the constituents of reality as having
some psychic, or at least proto-psychic, properties distinct from
whatever physical properties they may have (Nagel 1979). Indeed
neutral monism might be consistently combined with some version
of *panprotopsychism* (Chalmers 1996) according to which the
proto-mental aspects of micro-constituents can give rise under
suitable conditions of combination to full blown consciousness. (See
the entry on
 panpsychism.)



The nature of the relevant proto-psychic aspect remains unclear, and
such theories face a dilemma if offered in hope of answering the Hard
Problem. Either the proto-psychic properties involve the sort of
qualitative phenomenal feel that generates the Hard Problem or they do
not. If they do, it is difficult to understand how they could possibly
occur as ubiquitous properties of reality. How could an electron or a
quark have any such experiential feel? However, if the proto-psychic
properties do not involve any such feel, it is not clear how they are
any better able than physical properties to account for qualitative
consciousness in solving the Hard Problem.



A more modest form of panpsychism has been advocated by the
neuroscientist Giulio Tononi (2008) and endorsed by other
neuroscientists including Christof Koch (2012). This version derives
from Tononi's integrated information theory (IIT) of consciousness
that identifies consciousness with integrated information which can
exist in many degrees (see section 9.6 below). According to IIT, even
a simple indicator device such as a single photo diode possesses some
degree of integrated information and thus some limited degree of
consciousness, a consequence which both Tononi and Koch embrace as a
form of panpsychism. 




A variety of arguments have been given in favor of dualist and other
anti-physicalist theories of consciousness. Some are largely*a
priori* in nature such as those that appeal to the supposed
conceivability of zombies (Kirk 1970, Chalmers 1996) or versions of the
knowledge argument (Jackson 1982, 1986) which aim to reach an
anti-physicalist conclusion about the ontology of consciousness from
the apparent limits on our ability to fully understand the qualitative
aspects of conscious experience through third-person physical accounts
of the brain processes. (See Jackson 1998, 2004 for a contrary view;
see also entries on
 zombies,
 and
 qualia: the knowledge argument.)
 Other arguments for dualism are made on more empirical grounds, such
as those that appeal to supposed causal gaps in the chains of physical
causation in the brain (Eccles and Popper 1977) or those based on
alleged anomalies in the temporal order of conscious awareness (Libet
1982, 1985). Dualist arguments of both sorts have been much disputed
by physicalists (P.S. Churchland 1981, Dennett and Kinsbourne
1992).


### 8.2 Physicalist theories




Most other metaphysical theories of consciousness are versions of
physicalism of one familiar sort or another.



*Eliminativist* theories reductively deny the existence of
consciousness or at least the existence of some of its commonly
accepted sorts or features. (See the entry on
 eliminative materialism.)
 The radical eliminativists reject the very notion of consciousness as
muddled or wrong headed and claim that the conscious/nonconscious
distinction fails to cut mental reality at its joints (Wilkes 1984,
1988). They regard the idea of consciousness as sufficiently off
target to merit elimination and replacement by other concepts and
distinctions more reflective of the true nature of mind
(P. S. Churchland 1983).




Most eliminativists are more qualified in their negative assessment.
Rather than rejecting the notion outright, they take issue only with
some of the prominent features that it is commonly thought to involve,
such as qualia (Dennett 1990, Carruthers 2000), the conscious self
(Dennett 1992), or the so called "Cartesian Theater" where
the temporal sequence of conscious experience gets internally
projected (Dennett and Kinsbourne 1992). More modest eliminativists,
like Dennett, thus typically combine their qualified denials with a
positive theory of those aspects of consciousness they take as real,
such as the Multiple Drafts Model (section
 9.3
 below).



*Identity theory*, at least strict psycho-physical type-type
identity theory, offers another strongly reductive option by
identifying conscious mental properties, states and processes with
physical ones, most typically of a neural or neurophysiological
nature. If having a qualitative conscious experience of phenomenal
red *just is* being in a brain state with the relevant
neurophysiological properties, then such experiential properties are
real but their reality is a straight forwardly physical reality.



*Type-type identity theory* is so called because it identifies
mental and physical types or properties on a par with identifying the
property of being water with the property of being composed of
H2O molecules. After a brief period of popularity in the
early days of contemporary physicalism during the 1950s and 60s (Place
1956, Smart 1959) it has been far less widely held because of problems
such as the multiple realization objection according to which mental
properties are more abstract and thus capable of being realized by
many diverse underlying structural or chemical substrates (Fodor 1974,
Hellman and Thompson 1975). If one and the same conscious property
can be realized by different neurophysiological (or even
non-neurophysiological) properties in different organisms, then the
two properties can not be strictly identical.




Nonetheless the type-type identity theory has enjoyed a recent if
modest resurgence at least with respect to qualia or qualitative
conscious properties. This has been in part because treating the
relevant psycho-physical link as an identity is thought by some to
offer a way of dissolving the explanatory gap problem (Hill and
McLaughlin 1998, Papineau 1995, 2003). They argue that if the
conscious qualitative property and the neural property are identical,
then there is no need to explain how the latter causes or gives rise
to the former. It does not *cause* it, it *is* it. And
thus there is no gap to bridge, and no further explanation is needed.
Identities are not the sort of thing that can be explained, since
nothing is identical with anything but itself, and it makes no sense
to ask why something is identical with itself.




However, others contend that the appeal to type-type identity does not
so obviously void the need for explanation (Levine 2001). Even if two
descriptions or concepts in fact refer to one and the same property,
one may still reasonably expect some explanation of that convergence,
some account of how they pick out one and the same thing despite not
initially or intuitively seeming to do so. In other cases of
empirically discovered property identities, such as that of heat and
kinetic energy, there is a story to be told that explains the
co-referential convergence, and it seems fair to expect the same in
the psycho-physical case. Thus appealing to type-type identities may
not in itself suffice to dissolve the explanatory gap problem.




Most physicalist theories of consciousness are neither eliminativist
nor based on strict type-type identities. They acknowledge the reality
of consciousness but aim to locate it within the physical world on the
basis of some psycho-physical relation short of strict property
identity.




Among the common variants are those that take conscious reality to
*supervene* on the physical, be *composed of* the
physical, or be *realized by* the physical.



*Functionalist* theories in particular rely heavily on the
notion of *realization* to explicate the relation between
consciousness and the physical. According to functionalism, a state or
process counts as being of a given mental or conscious type in virtue
of the functional role it plays within a suitably organized system
(Block 1980a). A given physical state realizes the relevant conscious
mental type by playing the appropriate role within the larger physical
system that contains it. (See the entry on 
 functionalism.)
 The functionalist often appeals to analogies with other inter-level
relations, as between the biological and biochemical or the chemical
and the atomic. In each case properties or facts at one level are
realized by complex interactions between items at an underlying
level.




Critics of functionalism often deny that consciousness can be
adequately explicated in functional terms (Block 1980a, 1980b, Levine
1983, Chalmers 1996). According to such critics, consciousness may have
interesting functional characteristics but its nature is not
essentially functional. Such claims are sometimes supported by appeal
to the supposed possibility of absent or inverted qualia, i.e., the
possibility of beings who are functionally equivalent to normal humans
but who have reversed qualia or none at all. The status of such
possibilities is controversial (Shoemaker 1981, Dennett 1990,
Carruthers 2000), but if accepted they would seem to pose a problem for
the functionalist. (See the entry on
 qualia.)




Those who ground ontological physicalism on the realization relation
often combine it with a nonreductive view at the conceptual or
representational level that stresses the autonomy of the special
sciences and the distinct modes of description and cognitive access
they provide.



*Non-reductive physicalism* of this sort denies that the
theoretical and conceptual resources appropriate and adequate for
dealing with facts at the level of the underlying substrate or
realization level must be adequate as well for dealing with those at
the realized level (Putnam 1975, Boyd 1980). As noted above in response
to the How question, one can believe that all economic facts are
physically realized without thinking that the resources of the physical
sciences provide all the cognitive and conceptual tools we need for
doing economics (Fodor 1974).




Nonreductive physicalism has been challenged for its alleged failure
to "pay its physicalist dues" in reductive coin. It is
faulted for supposedly not giving an adequate account of how conscious
properties are or could be realized by underlying neural, physical or
functional structures or processes (Kim 1987, 1998). Indeed it has
been charged with incoherence because of its attempt to combine a
claim of physical realization with the denial of the ability to spell
out that relation in a strict and *a priori* intelligible way
(Jackson 2004).




However, as noted above in discussion of the How question,
nonreductive physicalists reply by agreeing that some account of
psycho-physical realization is indeed needed, but adding that the
relevant account may fall far short of *a priori* deducibility,
yet still suffice to satisfy our legitimate explanatory demands (McGinn
1991, Van Gulick 1985). The issue remains under debate.


## 9. Specific Theories of Consciousness




Although there are many general metaphysical/ontological theories of
consciousness, the list of specific detailed theories about its nature
is even longer and more diverse. No brief survey could be close to
comprehensive, but seven main types of theories may help to indicate the
basic range of options: higher-order theories, representational
theories, interpretative narrative theories, cognitive theories,
neural theories, quantum theories and nonphysical theories. The
categories are not mutually exclusive; for example, many cognitive
theories also propose a neural substrate for the relevant cognitive
processes. Nonetheless grouping them in the seven classes provides a
basic overview.


### 9.1 Higher-order theories




Higher-order (HO) theories analyze the notion of a conscious mental
state in terms of reflexive meta-mental self-awareness. The core idea
is that what makes a mental state M a conscious mental state is the
fact that it is accompanied by a simultaneous and non-inferential
higher-order (i.e., meta-mental) state whose content is that one is now
in M. Having a conscious desire for some chocolate involves being in
two mental states; one must have both a desire for some chocolate and
also a higher-order state whose content is that one is now having just
such a desire. Unconscious mental states are unconscious precisely in
that we lack the relevant higher-order states about them. Their being
unconscious consists in the fact that we are not reflexively and
directly aware of being in them. (See the entry on
 higher-order theories of consciousness.)




Higher-order theories come in two main variants that differ
concerning the psychological mode of the relevant conscious-making
meta-mental states. Higher-order thought (HOT) theories take the
required higher-order state to be an assertoric thought-like meta-state
(Rosenthal 1986, 1993). Higher-order perception (HOP) theories take
them to be more perception-like and associated with a kind of inner
sense and intra-mental monitoring systems of some sort (Armstrong 1981,
Lycan 1987, 1996).




Each has its relative strengths and problems. HOT theorists note
that we have no organs of inner sense and claim that we experience no
sensory qualities other than those presented to us by outer directed
perception. HOP theorists on the other hand can argue that their view
explains some of the additional conditions required by HO accounts as
natural consequences of the perception-like nature of the relevant
higher-order states. In particular the demands that the
conscious-making meta-state be noninferential and simultaneous with its
lower level mental object might be explained by the parallel conditions
that typically apply to perception. We perceive what is happening now,
and we do so in a way that involves no inferences, at least not any
explicit personal-level inferences. Those conditions are no less
necessary on the HOT view but are left unexplained by it, which might
seem to give some explanatory advantage to the HOP model (Lycan 2004,
Van Gulick 2000), though some HOT theorists argue otherwise (Carruthers
2000).




Whatever their respective merits, both HOP and HOT theories face some
common challenges, including what might be called the*generality
problem.* Having a thought or perception of a given
item *X*--be it a rock, a pen or a potato--does not
in general make *X* a conscious *X*. Seeing or thinking
of the potato on the counter does not make it a conscious potato. Why
then should having a thought or perception of a given desire or a
memory make it a conscious desire or memory (Dretske 1995, Byrne
1997). Nor will it suffice to note that we do not apply the term
"conscious" to rocks or pens that we perceive or think of,
but only to mental states that we perceive or think of (Lycan 1997,
Rosenthal 1997). That may be true, but what is needed is some account
of why it is appropriate to do so.




The higher-order view is most obviously relevant to the meta-mental
forms of consciousness, but some of its supporters take it to explain
other types of consciousness as well, including the more subjective
what it's like and qualitative types. One common strategy is to analyze
qualia as mental features that are capable of occurring unconsciously;
for example they might be explained as properties of inner states whose
structured similarity relations given rise to beliefs about objective
similarities in the world (Shoemaker 1975, 1990). Though unconscious
qualia can play that functional role, there need be nothing that it is
like to be in a state that has them (Nelkin 1989, Rosenthal 1991,
1997). According to the HO theorist, *what-it's-likeness* enters
only when we become aware of that first-order state and its qualitative
properties by having an appropriate meta-state directed at it.




Critics of the HO view have disputed that account, and some have
argued that the notion of unconscious qualia on which it relies is
incoherent (Papineau 2002). Whether or not such proposed HO accounts of
qualia are successful, it is important to note that most HO advocates
take themselves to be offering a comprehensive theory of consciousness,
or at least the core of such a general theory, rather than merely one
limited to some special meta-mental forms of it.




Other variants of HO theory go beyond the standard HOT and HOP
versions including some that analyze consciousness in terms of
dispositional rather than occurrent higher-order thoughts (Carruthers
2000). Others appeal to implicit rather than explicit higher-order
understanding and weaken or remove the standard assumption that the
meta-state must be distinct and separate from its lower-order object
(Gennaro 1995, Van Gulick 2000, 2004) with such views overlapping with
so called reflexive theories discussed in the section. Other variants
of HO theory continue to be offered, and debate between supporters and
critics of the basic approach remains active. (See the recent papers
in Gennaro 2004.)


### 9.2 Reflexive theories


 

Reflexive theories, like higher-order theories, imply a strong link
between consciousness and self-awareness. They differ in that they
locate the aspect of self-awareness directly within the conscious
state itself rather than in a distinct meta-state directed at it. The
idea that conscious states involve a double intentionality goes back
at least to Brentano (1874) in the 19th century. The conscious state
is intentionally directed at an object outside itself--such as a
tree or chair in the case of a conscious perception--as well as
intentionally directed at itself. One and the same state is both an
outer-directed awareness and an awareness of itself. Several recent
theories have claimed that such reflexive awareness is a central
feature of conscious mental states. Some view themselves as variants
of higher-order theory (Gennaro 2004, 2012) while others reject the
higher-order category and describe their theories as presenting a
"same-order" account of consciousness as self-awareness
(Kriegel 2009). Yet others challenge the level distinction by
analyzing the meta-intentional content as implicit in the phenomenal
first-order content of conscious states, as in so called Higher-Order
Global State models (HOGS) (Van Gulick 2004,2006). A sample of papers,
some supporting and some attacking the reflexive view can be found in
Krigel and Williford (2006).


### 9.3 Representationalist theories




Almost all theories of consciousness regard it as having
representational features, but so called representationalist theories
are defined by the stronger view that its representational features
exhaust its mental features (Harman 1990, Tye 1995, 2000). According to
the representationalist, conscious mental states have no mental
properties other than their representational properties. Thus two
conscious or experiential states that share all their representational
properties will not differ in any mental respect.




The exact force of the claim depends on how one interprets the idea
of being "representationally the same" for which there are
many plausible alternative criteria. One could define it coarsely in
terms of satisfaction or truth conditions, but understood in that way
the representationalist thesis seems clearly false. There are too many
ways in which states might share their satisfaction or truth conditions
yet differ mentally, including those that concern their mode of
conceptualizing or presenting those conditions.




At the opposite extreme, one could count two states as
representationally distinct if they differed in any features that
played a role in their representational function or operation. On such
a liberal reading any differences in the bearers of content would count
as representational differences even if they bore the same intentional
or representational content; they might differ only in their
*means* or *mode* of representation not their
*content*.




Such a reading would of course increase the plausibility of the
claim that a conscious state's representational properties exhaust its
mental properties but at the cost of significantly weakening or even
trivializing the thesis. Thus the representationalist seems to need an
interpretation of *representational sameness* that goes beyond
mere satisfaction conditions and reflects all the intentional or
contentful aspects of representation without being sensitive to mere
differences in underlying non-contentful features of the processes at
the realization level. Thus most representationalists provide conditions
for conscious experience that include both a content condition plus
some further causal role or format requirements (Tye 1995, Dretske
1995, Carruthers 2000). Other representationalists accept the existence
of qualia but treat them as objective properties that external objects
are represented as having, i.e., they treat them as
*represented* *properties* rather than as *properties
of representations* or mental states (Dretske 1995, Lycan
1996).




Representationalism can be understood as a qualified form of
eliminativism insofar as it denies the existence of properties of a
sort that conscious mental states are commonly thought to 
have--or at least seem to have--namely those that are mental but not
representational. Qualia, at least if understood as intrinsic monadic
properties of conscious states accessible to introspection, would seem
to be the most obvious targets for such elimination. Indeed part of the
motivation for representationalism is to show that one can accommodate
all the facts about consciousness, perhaps within a physicalist
framework, without needing to find room for qualia or any other
apparently non-representational mental properties (Dennett 1990, Lycan
1996, Carruthers 2000).




Representationalism has been quite popular in recent years and had
many defenders, but it remains highly controversial and intuitions
clash about key cases and thought experiments (Block 1996). In
particular the possibility of inverted qualia provides a crucial test
case. To anti-representationalists, the mere logical possibility of
inverted qualia shows that conscious states can differ in a significant
mental respect while coinciding representationally.
Representationalists in reply deny either the possibility of such
inversion or its alleged import (Dretske 1995, Tye 2000).




Many other arguments have been made for and against
representationalism, such as those concerning perceptions in different
sense modalities of one and the same state of affairs--seeing
and feeling the same cube--which might seem to involve mental
differences distinct from how the relevant states represent the world
to be (Peacocke 1983, Tye 2003). In each case, both sides can muster
strong intuitions and argumentative ingenuity. Lively debate
continues.


### 9.4 Narrative Interpretative Theories



Some theories of consciousness stress the interpretative nature of
facts about consciousness. According to such views, what is or is not
conscious is not always a determinate fact, or at least not so
independent of a larger context of interpretative judgments. The most
prominent philosophical example is the Multiple Drafts Model (MDM) of
consciousness, advanced by Daniel Dennett (1991). It combines elements
of both representationalism and higher-order theory but does so in a
way that varies interestingly from the more standard versions of
either providing a more interpretational and less strongly realist
view of consciousness.



The MDM includes many distinct but interrelated features. Its name
reflects the fact that at any given moment content fixations of many
sorts are occurring throughout the brain. What makes some of these
contents conscious is not that they occur in a privileged spatial or
functional location--the so called "Cartesian
Theater"--nor in a special mode or format, all of which the
MDM denies. Rather it a matter of what Dennett calls "cerebral
celebrity", i.e., the degree to which a given content influences
the future development of other contents throughout the brain,
especially with regard to how those effects are manifest in the
reports and behaviors that the person makes in response to various
probes that might indicate her conscious state. One of the MDM's key
claims is that different probes (e. g., being asked different
questions or being in different contexts that make differing
behavioral demands) may elicit different answers about the person's
conscious state. Moreover, according to the MDM there may be no
probe-independent fact of the matter about what the person's conscious
state really was. Hence the "multiple" of the Multiple
Drafts Model.



The MDM is representationalist in that it analyzes consciousness in
terms of content relations. It also denies the existence of qualia and
thus rejects any attempt to distinguish conscious states from
nonconscious states by their presence. It rejects as well the notion
of the self as an inner observer, whether located in the Cartesian
Theater or elsewhere. The MDM treats the self as an emergent or
virtual aspect of the coherent roughly serially narrative that is
constructed through the interactive play of contents in the
system. Many of those contents are bound together at the intentional
level as perceptions or fixations from a relatively unified and
temporally extended point of view, i.e., they cohere in their contents
as if they were the experiences of a ongoing self. But it is the order
of dependence that is crucial to the MDM account. The relevant
contents are not unified because they are all observed by a single
self, but just the converse. It is because they are unified and
coherent at the level of content that they count as the experiences of
a single self, at least of a single virtual self.



It is in this respect that the MDM shares some elements with
higher-order theories. The contents that compose the serial narrative
are at least implicitly those of an ongoing if virtual self, and it is
they that are most likely to be expressed in the reports the person
makes of her conscious state in response to various probes. They thus
involve a certain degree of reflexivity or self-awareness of the sort
that is central to higher-order theories, but the higher-order aspect
is more an implicit feature of the stream of contents rather than
present in distinct explicit higher-order states of the sort found in
standard HO theories.



Dennett's MDM has been highly influential but has also drawn
criticism, especially from those who find it insufficiently realist in
its view of consciousness and at best incomplete in achieving its
stated goal to fully explain it (Block 1994, Dretske 1994, Levine
1994). Many of its critics acknowledge the insight and value of the
MDM, but deny that there are no real facts of consciousness other than
those captured by it (Rosenthal 1994, Van Gulick 1994, Akins
1996).



From a more empirical perspective, the neuroscientist Michael
Gazzaniga (2011) has introduced the idea of an "interpreter
module" based in the left hemisphere that makes sense of our
actions in any inferential way and constructs an ongoing narrative of
our actions and experience. Though the theory is not intended as a
complete theory of consciousness, it accords a major role to such
interpretative narrative activity.


### 9.5 Cognitive Theories




A number theories of consciousness associate it with a distinct
cognitive architecture or with a special pattern of activity with that
structure.



*Global Workspace*. A major psychological example of the
cognitive approach is the Global Workspace theory. As initially
developed by Bernard Baars (1988)) global workspace theory describes
consciousness in terms of a competition among processors and outputs
for a limited capacity resource that "broadcasts" information for
widespread access and use. Being available in that way to the global
workspace makes information conscious at least in the access sense. It
is available for report and the flexible control of behavior. Much
like Dennett's "cerebral celebrity", being broadcast in the workspace
makes contents more accessible and influential with respect to other
contents and other processors. At the same time the original content
is strengthened by recurrent support back from the workspace and from
other contents with which it coheres. The capacity limits on the
workspace correspond to the limits typically placed on focal attention
or working memory in many cognitive models. 




The model has been further developed with proposed connections to
particular neural and functional brain systems by Stanislas Dehaene
and others (2000). Of special importance is the claim that
consciousness in both the access and phenomenal sense occurs when and
only when the relevant content enters the larger global network
involving both primary sensory areas as well as many other areas
including frontal and parietal areas associated with
attention. Dehaene claims that conscious perception begins only with
the "ignition" of that larger global network; activity in the primary
sensory areas will not suffice no matter how intense or recurrent
(though see the contrary view of Victor Lamme in section 9.7).



*Attended Intermediate Representation*. Another cognitive theory
is Jesse Prinz's (2012) Attended Intermediate level Representation
theory (AIR). The theory is a neuro-cognitive hybrid account of
conscious. According to AIR theory, a conscious perception must meet
both cognitive and neural conditions. It must be a representation of a
perceptually intermediate property which Prinz argues are the only
properties of which we are aware in conscious experience--we
experience only basic features of external objects such as colors,
shapes, tones, and feels. According to Prinz, our awareness of higher
level properties--such as being a pine tree or my car keys--is
wholly a matter of judging and not of conscious experience. Hence the
Intermediate Representational (IR) aspect of AIR. To be conscious
such a represented content must also be Attended (the A aspect of
AIR). Prinz proposes a particular neural substrate for each component.
He identifies the intermediate level representations with gamma
(40-80hz) vector activity in sensory cortex and the attentional
component with synchronized oscillations that can incorporate that
gamma vector activity. 


### 9.6 Information Integration Theory




The integration of information from many sources is an important
feature of consciousness and, as noted above (section 6.4), is often
cited as one of its major functions. Content integration plays an
important role in various theories especially global workspace theory
(section 9.3). However, a proposal by the neuroscientist Giulio
Tononi (2008) goes further in identifying consciousness with
integrated information and asserting that information integration of
the relevant sort is both necessary and sufficient for consciousness
regardless of the substrate in which it is realized (which need not be
neural or biological). According to Tononi's Integrated Information
Theory (IIT), consciousness is a purely information-theoretic property
of systems. He proposes a mathematical measure ph that aims to
measure not merely the information in the parts of a given system but
also the information contained in the organization of the system over
and above that in its parts. ph thus corresponds to the system's
degree of informational integration. Such a system can contain many
overlapping complexes and the complex with the highest ph value
will be conscious according to IIT.


 According to IIT, consciousness varies in quantity and comes in
many degrees which correspond to ph values. Thus even a simple
system such a single photo diode will be conscious to some degree if
it is not contained within a larger complex. In that sense, IIT
implies a form of panpsychism that Tononi explicitly endorses.
According to IIT, the quality of the relevant consciousness is
determined by the totality of informational relations within the
relevant integrated complex. Thus IIT aims to explain both the
quantity and quality of phenomenal consciousness. Other
neuroscientists, notably Christof Koch, have also endorsed the IIT
approach (Koch 2012).


### 9.7 Neural Theories


Neural theories of consciousness come in many forms, though most in
some way concern the so called "neural correlates of
consciousness" or NCCs. Unless one is a dualist or other
non-physicalist, more than mere correlation is required; at least some
NCCs must be the essential substrates of consciousness. An explanatory
neural theory needs to explain why or how the relevant correlations
exist, and if the theory is committed to physicalism that will require
showing how the underlying neural substrates could be identical with
their neural correlates or at least realize them by satisfying the
required roles or conditions (Metzinger 2000).




Such theories are diverse not only in the neural processes or
properties to which they appeal but also in the aspects of
consciousness they take as their respective explananda. Some are based
on high-level systemic features of the brain, but others focus on more
specific physiological or structural properties, with corresponding
differences in their intended explanatory targets. Most in some way
aim to connect with theories of consciousness at other levels of
description such as cognitive, representational or higher-order
theories.




A sampling of recent neural theories might include models that
appeal to global integrated fields (Kinsbourne), binding through
synchronous oscillation (Singer 1999, Crick and Koch 1990),
NMDA-mediated transient neural assemblies (Flohr 1995), thalamically
modulated patterns of cortical activation (Llinas 2001), reentrant
cortical loops (Edelman 1989), comparator mechanisms that engage in
continuous action-prediction-assessment loops between frontal and
midbrain areas (Gray 1995), left hemisphere based interpretative
processes (Gazzaniga 1988), and emotive somatosensory hemostatic
processes based in the frontal-limbic nexus (Damasio 1999) or in the
periaqueductal gray (Panksepp 1998).




In each case the aim is to explain how organization and activity at
the relevant neural level could underlie one or another major type or
feature of consciousness. Global fields or transient synchronous
assemblies could underlie the intentional unity of phenomenal
consciousness. NMDA-based plasticity, specific thalamic projections
into the cortex, or regular oscillatory waves could all contribute to
the formation of short term but widespread neural patterns or
regularities needed to knit integrated conscious experience out of the
local activity in diverse specialized brain modules. Left hemisphere
interpretative processes could provide a basis for narrative forms of
conscious self-awareness. Thus it is possible for multiple distinct
neural theories to all be true, with each contributing some partial
understanding of the links between conscious mentality in its diverse
forms and the active brain at its many levels of complex organization
and structure.



One particular recent controversy has concerned the issue of whether
global or merely local recurrent activity is sufficient for phenomenal
consciousness. Supporters of the global neuronal workspace model
(Dehaene 2000) have argued that consciousness of any sort can occur
only when contents are activated with a large scale pattern of
recurrent activity involving frontal and parietal areas as well as
primary sensory areas of cortex. Others in particular the
psychologist Victor Lamme (2006) and the philosopher Ned Block (2007)
have argued that local recurrent activity between higher and lower
areas within sensory cortex (e.g. with visual cortex) can suffice for
phenomenal consciousness even in the absence of verbal reportability
and other indicators of access consciousness. 


### 9.8 Quantum theories




Other physical theories have gone beyond the neural and placed the
natural locus of consciousness at a far more fundamental level, in
particular at the micro-physical level of quantum phenomena. According
to such theories, the nature and basis of consciousness can not be
adequately understood within the framework of classical physics but
must be sought within the alternative picture of physical reality
provided by quantum mechanics. The proponents of the quantum
consciousness approach regard the radically alternative and often
counterintuitive nature of quantum physics as just what is needed to
overcome the supposed explanatory obstacles that confront more standard
attempts to bridge the psycho-physical gap.




Again there are a wide range of specific theories and models that
have been proposed, appealing to a variety of quantum phenomena to
explain a diversity of features of consciousness. It would be
impossible to catalog them here or even explain in any substantial way
the key features of quantum mechanics to which they appeal. However, a
brief selective survey may provide a sense, however partial and
obscure, of the options that have been proposed.




The physicist Roger Penrose (1989, 1994) and the anesthesiologist
Stuart Hameroff (1998) have championed a model according to which
consciousness arises through quantum effects occurring within
subcellular structures internal to neurons known as
*microtubules*. The model posits so called "*objective
collapses*" which involve the quantum system moving from a
superposition of multiple possible states to a single definite state,
but without the intervention of an observer or measurement as in most
quantum mechanical models. According to the Penrose and Hameroff, the
environment internal to the microtubules is especially suitable for
such objective collapses, and the resulting self-collapses produce a
coherent flow regulating neuronal activity and making non-algorithmic
mental processes possible.




The psychiatrist Ian Marshall has offered a model that aims to
explain the coherent unity of consciousness by appeal to the production
within the brain of a physical state akin to that of a
*Bose-Einstein condensate*. The latter is a quantum phenomenon in
which a collection of atoms acts as a single coherent entity and the
distinction between discrete atoms is lost. While brain states are not
literally examples of Bose-Einstein condensates, reasons have been
offered to show why brains are likely to give rise to states that are
capable of exhibiting a similar coherence (Marshall and Zohar
1990).




A basis for consciousness has also been sought in
the *holistic* nature of quantum mechanics and the phenomenon of
*entanglement*, according to which particles that have
interacted continue to have their natures depend upon each other even
after their separation. Unsurprisingly these models have been targeted
especially at explaining the coherence of consciousness, but they have
also been invoked as a more general challenge to the atomistic
conception of traditional physics according to which the properties of
wholes are to be explained by appeal to the properties of their parts
plus their mode of combination, a method of explanation that might be
regarded as unsuccessful to date in explaining consciousness
(Silberstein 1998, 2001).




Others have taken quantum mechanics to indicate that consciousness
is an absolutely fundamental property of physical reality, one that
needs to be brought in at the very most basic level (Stapp 1993). They
have appealed especially to the role of the observer in the collapse of
the wave function, i.e., the collapse of quantum reality from a
superposition of possible states to a single definite state when a
measurement is made. Such models may or may not embrace a form of
quasi-idealism, in which the very existence of physical reality depends
upon its being consciously observed.




There are many other quantum models of consciousness to be found in
the literature--some advocating a radically revisionist
metaphysics and others not--but these four provide a reasonable,
though partial, sample of the alternatives.


### 9.9 Non-physical theories




Most specific theories of consciousness--whether cognitive,
neural or quantum mechanical--aim to explain or model
consciousness as a natural feature of the physical world. However,
those who reject a physicalist ontology of consciousness must find ways
of modeling it as a nonphysical aspect of reality. Thus those who adopt
a dualist or anti-physicalist metaphysical view must in the end provide
specific models of consciousness different from the five types above.
Both substance dualists and property dualists must develop the details
of their theories in ways that articulate the specific natures of the
relevant non-physical features of reality with which they equate
consciousness or to which they appeal in order to explain it.




A variety of such models have been proposed including the following.
David Chalmers (1996) has offered an admittedly speculative version of
panpsychism which appeals to the notion of information not only to
explain psycho-physical invariances between phenomenal and physically
realized information spaces but also to possibly explain the ontology
of the physical as itself derived from the informational (a version of
"it from bit" theory). In a somewhat similar vein, Gregg
Rosenberg has (2004) proposed an account of consciousness that
simultaneously addresses the ultimate categorical basis of causal
relations. In both the causal case and the conscious case, Rosenberg
argues the relational-functional facts must ultimately depend upon a
categorical non-relational base, and he offers a model according to
which causal relations and qualitative phenomenal facts both depend
upon the same base. Also, as noted just above (section 9.8), some
quantum theories treat consciousness as a fundamental feature of
reality (Stapp 1993), and insofar as they do so, they might be
plausibly classified as non-physical theories as well.


## 10. Conclusion




A comprehensive understanding of consciousness will likely require
theories of many types. One might usefully and without contradiction
accept a diversity of models that each in their own way aim
respectively to explain the physical, neural, cognitive, functional,
representational and higher-order aspects of consciousness. There is
unlikely to be any single theoretical perspective that suffices for
explaining all the features of consciousness that we wish to
understand. Thus a synthetic and pluralistic approach may provide the
best road to future progress.