## 1. The Metaphysics of Memory: An Overview



More than any other area, the metaphysics of memory reflects the trend
towards interdisciplinarity noted above, and work in this area
sometimes shades into philosophy of psychology (Rowlands 2009) and
philosophy of neuroscience (Bickle 2011). Relevant work in the
philosophy of psychology is discussed here as appropriate; for more
specialized work in the philosophy of neuroscience, see
the entry on that topic. The central
aim of mainstream research on the metaphysics of memory is to develop
a *theory of remembering*: a general but informative account of
what it is for someone to remember something. As we will see, however,
there are multiple kinds of memory. It is unclear whether it is feasible to
develop a theory of remembering that applies to all of these, and
ultimately it may prove necessary to develop multiple theories of
remembering, corresponding to the multiple kinds of memory. (Something
similar may go for the epistemology of memory [Teroni 2014].)



The particular kind of memory on which most recent work has focused
has gone by a number of names, but, adopting Tulving's
(1972, 1985a) psychological terminology, philosophers increasingly refer to
it as "episodic" (e.g., Hoerl
2007; Dokic 2014; Hopkins 2014; Perrin & Rousset 2014;
Soteriou 2008). The terminology may be new, but the focus is not (Brewer 1996).
Episodic memory is, roughly, memory for the events of the personal past, and,
starting at least with Aristotle (Sorabji 2006) and continuing with early modern
philosophers including Locke (1998), Hume ([1739] 2011), and Reid ([1785] 2002),
philosophers have singled episodic memory out for special attention on the ground
that it provides the rememberer with a unique form of access to past events.
For some, indeed, only episodic memory truly merits the name
"memory" (Klein 2015; B.
Russell 1921). Reflecting this focus, this entry will be concerned
primarily with theories of *episodic* remembering: accounts of
what it is for someone to remember an event from his personal
past.



Due, perhaps, to their focus on episodic memory, philosophers have
generally approached memory as a capacity exercised by single
individuals. But recent work in a variety of disciplines has begun to
challenge the individualistic approach, and the metaphysics of memory
has come to include issues arising from the tradition of research on
collective memory in the human and social sciences which traces back
to Halbwachs ([1925] 1994; cf. Barash 2016; Michaelian
& Sutton forthcoming) and which has recently given
birth to the multidisciplinary field of memory studies (Roediger
& Wertsch 2008; Segesten &
Wustenberg forthcoming). It has also come to
include issues arising from the more recent tradition of research on
external memory in cognitive science which views remembering through
the lens of distributed (Hutchins 1995) or extended (Clark
& Chalmers 1998) theories of cognition.
While the entry is concerned primarily with individual memory, these
more recent issues will be discussed as well.


## 2. Kinds of Memory



Before turning to theories of episodic remembering, it will be helpful
to situate episodic memory with respect to other kinds of memory. In
its broadest sense, "memory"
refers to the varied outcomes of the diverse forms of learning of which humans
and other agents are capable. Any modification of an agent's
behavioural tendencies as a result of its experience thus potentially counts as
memory, making the category of memory very broad indeed. Despite the breadth
of the category, however, there is an approximate consensus on a taxonomy of kinds
of human memory.


### 2.1 The standard taxonomy



Philosophers generally distinguish among three main kinds of memory.
In early treatments, Bergson ([1896] 1911) and Russell (1921), for
example, distinguished between *habit* memory and
*recollective* memory, while Broad (1925) and Furlong (1951)
further distinguished between recollective memory and
*propositional* memory (cf. Ayer (1956; D. Locke 1971)). These
distinctions align reasonably well with those drawn by a taxonomy
which, originating in psychology, has increasingly become standard in
more recent philosophy.


#### 2.1.1 Declarative memory



The taxonomy in question, developed in detail by Squire (2009),
divides the overarching category of memory into *declarative*
and *nondeclarative* memory. Declarative memory, in turn, is
divided into *episodic* memory, corresponding roughly to
recollective memory, and *semantic* memory, corresponding
roughly to propositional memory. A first pass at distinguishing
episodic from semantic memory can be made by observing that the former
is concerned with the events of one's personal
past in particular (e.g., I remember speaking at a conference in Budapest),
while the later is concerned with the world in general (I remember
that Budapest is the capital of Hungary). It is crucial to note,
however, that semantic memory is also sometimes concerned with past
events. One can have memories that concern events that one did not
oneself experience (I remember that my colleague spoke at a workshop
in Rome, though I did not hear him speak); when one does, one
remembers semantically, not episodically. Similarly, one can have
memories that concern events that one did experience but that are of
the same kind as memories for events that one did not experience (I
remember that I visited the CN Tower when I was a child, but only
because my parents later related the story to me); when one does, one
likewise remembers semantically, not episodically. Thus the first-pass
distinction between episodic and semantic memory does not get us very
far. Drawing a more adequate distinction--providing
a criterion of *episodicity*--is a core
problem for the theories of episodic remembering discussed below.


#### 2.1.2 Nondeclarative memory



Nondeclarative memory is usually defined in negative terms: a form of
memory is declarative if it involves the encoding, storage, and
retrieval of content that the subject can, at least in principle,
bring to consciousness; it is nondeclarative if it does not (Squire
2009). Beyond this negative feature, the various kinds of
nondeclarative memory may not have much in common with each other. For
example, nondeclarative memory includes priming, which occurs when a
subject's response to a given stimulus is affected
by his previous exposure to related stimuli (e.g., I recognize the word
"Toronto" more quickly
after seeing "CN Tower"
than after seeing "Colosseum").
It also includes *procedural* memory, corresponding roughly to habit
memory, the kind of memory at work when a subject manifests his ability to
perform a skilled action (I remember how to ride a bicycle).



There is relatively little philosophical research on procedural
memory, and this kind of memory will not be discussed in any detail
here. This should not, however, be taken to imply that it is not of
major philosophical interest. In epistemological terms, while
declarative memory maps onto the category of knowledge that,
procedural memory maps onto the category of knowledge
how: one may know or remember how to do something without consciously
entertaining any relevant content and without being able, even in
principle, to consciously entertain any such content. Future research
on procedural memory might therefore build on classic (Ryle [1949]
2009) and contemporary (Stanley 2011) work on the relationship between
knowledge that and knowledge how.



Such research might also build on recent work on
embodied
(Myin & Zahidi 2015; Sutton 2007; Sutton
& Williamson 2014) and enactive cognition (Hutto 
special-character:amp] Myin 2017; Loader 2013). While
enactivist approaches will not be discussed any further here, it
should be noted there is potential for convergence between these
approaches and older Wittgensteinian approaches to memory.
Wittgenstein (1980) suggested--in opposition
to trace-based accounts--that remembering can,
under certain circumstances, amount to doing or saying something,
rather than retrieving stored content (Moyal-Sharrock 2009;
O'Loughlin forthcoming). This
resonates with the enactivist insistence on the centrality of action
to cognition, but connectionist readings
of Wittgenstein on memory (Stern 1991) have also been proposed, and it
remains to be seen whether supplementing enactivist approaches with
Wittgenstein will shed any additional light on the nature of remembering
(Sutton 2015).


### 2.2 Alternative taxonomies



Squire's taxonomy has been extremely influential,
but alternative taxonomies have been proposed in both psychology and
philosophy. In psychology, Atkinson and Shiffrin (1968) proposed a
multi-store model in which kinds of memory are distinguished in terms
of their temporal duration. Ultra short term memory refers to the
persistence of modality-specific sensory information for periods of
less than one second. Short term memory refers to the persistence of
information for up to thirty seconds; short term memory, which
receives information from ultra short term memory, is to some extent
under conscious control but is characterized by a limited capacity.
Long term memory refers to the storage of information over
indefinitely long periods of time; long term memory receives
information from short term memory and is characterized by an
effectively unlimited capacity. Though this taxonomy does not
distinguish among importantly different kinds of long term
memory--in particular, it does not distinguish
between episodic and semantic memory--it has been
applied productively in psychological research. With rare exceptions
(Werning & Cheng 2017), however, it has not
informed philosophical discussions.



In philosophy, Bernecker (2010) has proposed a purely grammatical
approach, arguing that the kinds of memory are given by the kinds of
objects that the verb "to 
remember" can take. He thus
distinguishes among memory for objects, memory for properties, memory
for events, and memory for propositions or facts. While a grammatical
approach will strike many in philosophy as natural, this particular
taxonomy has so far not been taken up very widely. This may be due in
part to the fact that, because the basis for the taxonomy is purely
linguistic, it has difficulty distinguishing between episodic memory
as such, which is arguably characterized by a particular
phenomenology, and mere event memory, which lacks this phenomenology
(Schechtman 2011). It may also be due in part to the fact that,
because it cuts across the categories employed by the standard
taxonomy, it is difficult to apply Bernecker's
taxonomy to studies that rely on the latter.


### 2.3 Other kinds of memory



Regardless of its merits, the standard taxonomy omits certain kinds of
memory that are bound to figure in any full-fledged theory of
remembering.


#### 2.3.1 Working memory



Working memory, corresponding roughly to Atkinson and
Shiffrin's short term memory, refers to a
capacity to actively manipulate a limited number of items in a
conscious workspace (Baddeley 2007). There is some philosophical
research on working memory (Block 2007; Carruthers 2015; Feest 2011),
but the topic has so far been largely unexplored in mainstream
philosophy of memory, and it will therefore not be discussed any
further in this entry.


#### 2.3.2 Prospective memory



Prospective memory refers to the ability to remember to perform a
planned action, or to execute an intention. Failures in prospective
memory are of considerable everyday significance and often cause some
personal concern. Experimental and naturalistic work on prospective
memory now flourishes in psychology (McDaniel &
Einstein 2007), and there is considerable discussion about how it relates
to other forms of memory and to other cognitive processes. Prospective
memory has not yet been addressed much in philosophy, but this is likely to
change given its relevance to understanding links between intention
and action and to other forms of future-oriented thought.


#### 2.3.3 Autobiographical memory



Autobiographical memory refers to one's knowledge
not only of specific past episodes but also of whole life periods, as well
as the overall course of one's life (Berntsen
& Rubin 2012). There is a good deal of philosophical
research on autobiographical memory, often drawing on accounts of narrativity.
The relationship between autobiographical memory and other kinds of memory
is described in different ways by different authors, but in most cases
autobiographical memory is treated as a complex capacity that emerges
through the interaction of more basic kinds of memory. It is thus
unlikely to be a kind of memory on a par with those acknowledged by
the standard taxonomy, which correspond to specific brain systems.
Existing accounts of autobiographical memory are discussed in
section 7 below.


### 2.4 Natural kinds in memory research



Psychologists have studied hundreds of different kinds of memory in
addition to those described above. Many of these are defined in terms
of specific laboratory tasks and are unlikely to qualify as
*natural kinds* (Tulving 2007), kinds that carve
nature--in this case, the
mind--at its joints. But even if only the
kinds acknowledged by the standard taxonomy are considered,
it is not obvious whether any particular kind of memory, never mind
memory as a whole, is a natural kind.



The obvious starting point here is the view that memory is indeed a
natural kind. Michaelian (2011b) has, however, suggested that memory
is not a natural kind, arguing that, because only declarative memory
involves the encoding, storage, and retrieval of content, declarative
and nondeclarative memory are sharply distinct from each other. This
is consistent with the view that declarative memory is a natural kind,
but Klein (2015) has rejected even the latter view, claiming that,
because episodic memory necessarily involves a particular
phenomenology, episodic memory and semantic memory are sharply
distinct. In response, Michaelian (2015) has appealed to cases in
which subjects appear to have intact episodic memory despite having
impaired episodic phenomenology (Klein & Nichols 2012)
to argue that the phenomenology in question is not, strictly speaking, a
necessary feature of episodic memory. If this suggestion is right,
then declarative memory may after all be natural kind. But even if
declarative memory turns out not to be a natural kind, episodic memory
might still be a natural kind. Cheng and Werning (2016), for example,
have argued on the basis of their "sequence
analysis" of remembering--a
variant of the causal theory of memory introduced in section 4
 below--that episodic memory is indeed a natural kind.



While there is some work on the question of the natural kindhood of
episodic memory, the question of the natural kindhood of kinds of
memory other than episodic memory remains almost entirely unexplored.
Future work here might both draw on and contribute to resolving the
debate between systems and process views of memory (Bechtel 2001;
Foster & Jelicic 1999; Schacter &
Tulving 1994). According to systems views, memory consists of multiple
independent systems which interact in various ways. According to process
views, in contrast, memory is a unitary capacity which is employed in
different ways in response to different demands. The once-lively debate
between partisans of systems views and partisans of process views has now
largely died down. It has not, however, been clearly resolved in
favour of either camp, and progress towards resolving it might be made
by bringing the available evidence into contact with detailed theories
of natural kinds.


## 3. Episodicity



As noted above, the kind of memory on which most recent work has
focussed is episodic memory. Episodic memory is, roughly, memory for
the events of the personal past, but not just any way of thinking
about an event from the personal past amounts to episodically
remembering it. On the one hand, it is possible, as noted above, for a
subject to remember an event not only episodically but also
semantically. Thus one core problem for a theory of episodic
remembering is to distinguish between episodic memory and semantic
memory, that is, to provide a criterion for the *episodicity*
of episodic memory. The present section discusses attempts to solve
this problem, which has received a great deal of attention in recent
years. On the other hand, it is possible not only to remember an event
but also to imagine it. Thus another core problem for a theory of
episodic remembering is to distinguish between episodic memory and
episodic imagination, that is, to provide a criterion for the
*mnemicity* of episodic memory. Section 4
discusses attempts to solve this problem, which has historically
received more attention.


### 3.1 First-order content



In Tulving's early work (Tulving 1972), episodic
memory was understood as *what-where-when*
memory--in other words, as a system dedicated to
storing and retrieving information about particular past events.
Episodic memory was thus distinguished from semantic memory in terms of
the kind of first-order content with which it is concerned. This
*first-order* content-based approach to episodicity is
appealingly straightforward, but it fails to acknowledge that semantic
memory can also provide information about particular past events. It
fails, moreover, to capture what has seemed to many to be the most
distinctive feature of episodic memory, namely, its characteristic
phenomenology.



In light of these problems, many researchers have abandoned
first-order content-based approaches in favour of the
*second-order* content-based and *phenomenological*
approaches discussed below. Some researchers, however, particularly
those interested in animal memory, continue to employ first-order
content-based approaches. The second-order content-based approach, as
we will see, imposes significant conceptual demands on rememberers,
demands which animals are unlikely to meet. And the phenomenological
approach is straightforwardly inapplicable to animal memory, since we
lack access to animal phenomenology.
 The what-where-when criterion of episodicity, in contrast, is
experimentally tractable, and research employing it has furnished
important insights into the abilities of various nonhuman species to
remember past events. Some researchers have found it expedient to
introduce a concept of *episodic-like* memory meant to be free
of any phenomenological connotations (Clayton & Dickinson 1998).
The concept of episodic-like memory may provide a means of reconciling
research on animal episodic memory with the influential
Bischof-Kohler hypothesis (Suddendorf
& Corballis 2007), according to which animals are
"stuck in time". The
Bischof-Kohler hypothesis is itself controversial (Hoerl 2008),
however, and the legitimacy of the concept of episodic-like memory
remains a matter of contention (Droege 2012; Keven 2016; Malanowski
2016; J. Russell & Hanna 2012).


### 3.2 Second-order content



Second-order content-based approaches understand episodic memory as
providing the rememberer with two types of information: first-order
information about the remembered event itself (as in the first-order
content-based approach) and second-order information about the
relationship between the event and the subject's current memory
of it. These approaches thus distinguish episodic memory from semantic
memory in terms of the *self-reflexive* character of its
content. McCormack and Hoerl, for example, emphasize the
rememberer's grasp of his temporal relationship to the event
(Hoerl 2001; McCormack & Hoerl 2001, 2008), while
Fernandez emphasizes the rememberer's
grasp of his causal relationship to the event (2006, 2008a,b).



The self-reflexivity criterion of episodicity is intuitively
appealing, but it is not without potentially problematic implications.
It implies, as noted above, that nonhuman animals (as well as young
children) are incapable of remembering episodically, since only
creatures with relatively sophisticated conceptual
capacities--including the ability to represent past times as past
and to represent the self as an enduring entity--are capable of
entertaining the relevant second-order contents. It also implies that
there is a major difference between the contents of retrieved memories
and the contents of the corresponding original experiences, since it
sees memories as including content--namely, their second-order,
self-reflexive component--that is not included in experiences.
Some have, however, seen the latter implication in a positive light,
arguing that the fact that episodic memory generates new
knowledge--by informing the subject not only of *what*
happened in the past but also *that* he knows what happened
because he experienced it--is in fact one of its defining
features (Dokic 2014; Fernandez 2015a).


### 3.3 Phenomenology



Phenomenological approaches, which have similar implications, have
been popular in recent psychology, with Tulving, *inter alia*,
abandoning the first-order approach in favour of an approach
emphasizing the phenomenology of episodic remembering (Tulving 2002;
cf. Dalla Barba 2002, 2016). Phenomenological approaches have likewise
long been popular in philosophy. Hume ([1739] 2011), for example,
argued that memory is accompanied by a feeling of strength and
liveliness. Russell (1921) associated memory with a feeling of
familiarity and a feeling of pastness. And Broad (1925) argued, more
specifically, that the feeling of pastness is inferred from the
feeling of familiarity. In the contemporary literature, Dokic (2014)
has argued that episodic memory involves an episodic feeling of
knowing.



The feeling of knowing, as usually understood, refers to the sense
that one will be able to retrieve needed information from memory. The
episodic feeling of knowing posited by Dokic, in contrast, refers to the
sense that one's retrieved memory of an event
originates in one's experience of the event.
The concept of an episodic feeling of knowing is thus close to the
concept of *autonoetic consciousness* first proposed by Tulving
(1985b). Autonoesis refers to the consciousness of the self in
subjective time--which can be roughly described
as a feeling of mentally travelling through time to reexperience an
event--that is characteristic of episodic
remembering. Klein (2015) has made a forceful case for treating
autonoeisis as a criterion of episodicity, and the idea that a sense
of mentally travelling through time is the distinguishing mark of
episodic memory fits well with our first-hand experience of the
reexperiential character of remembering.



This idea does, however, raise a number of difficult issues. One such
issue concerns the relationship of autonoetic consciousness to other
forms of consciousness. Tulving contrasts autonoetic (self-knowing)
consciousness with noetic (knowing) and anoetic (nonknowing)
consciousness, where noetic consciousness refers to the consciousness
of remembering that accompanies semantic memory and anoetic
consciousness refers to a basic awareness of ongoing experience. The
relationships among these forms of consciousness are complex
(Vandekerckhove & Panksepp 2009) and have yet to be explored in
detail by philosophers. Their relationships to the form of
temporal consciousness
at issue in awareness of the ongoing flow of time (Arstila &
Lloyd 2014; McCormack 2015) likewise have yet to be explored. Another
issue concerns the role of autonoesis in forms of *mental time
travel* other than episodic memory. Episodic memory is
increasingly understood as a form of past-oriented mental time travel
on a par with future-oriented mental time travel, or episodic future
thought (Suddendorf & Corballis 2007). While the standard view is
that autonoesis is a necessary feature of both episodic memory and
episodic future thought, some researchers have questioned the
necessity of autonoesis for episodic future thought (De Brigard &
Gessell 2016; Klein 2016a; Klein & Steindam 2016; Perrin
2016).


### 3.4 Functional perspectives on episodicity



Other researchers have argued that autonoesis is a contingent feature
even of episodic memory. This would undermine its
status as a criterion of episodicity, but, regardless of whether
autonoesis is taken to be a necessary or only a contingent feature of
episodic memory, it is not immediately obvious why we should be
capable of autonoetic episodic memory--as opposed to mere
what-where-when memory--at all. Indeed, accounting for any form
of episodic memory in functional terms has proven to be a difficult
challenge, and researchers have proposed a range of past-oriented,
future-oriented or counterfactual, and metacognitive accounts.



*Past-oriented* accounts appeal to functional incompatibilities
between episodic memory and procedural (Sherry & Schacter 1987) or
semantic (Klein, Cosmides, Tooby, & Chance 2002) memory. The
thought behind such accounts is that it is adaptively beneficial to
have access to information about particular past events, as opposed to
the recurrent features of events that are reflected in semantic or
procedural memory; such information might, for example, enable us to
reevaluate general impressions of others formed on the basis of their
past behaviour (Klein et al. 2009). Past-oriented accounts are
plausible as far as the function of what-where-when memory is
concerned, but they do not identify a function that could be performed
only when what-where-when information is accompanied by autonoetic
consciousness. *Future-oriented* and *counterfactual*
accounts appeal to the link between episodic memory and episodic
future thought (Suddendorf & Corballis 2007; Tulving 2005) or
episodic counterfactual thought (De Brigard 2014a). The thought behind
such accounts is that it is adaptively beneficial to prepare for
future events by directly anticipating them (in episodic future
thought) or by considering alternative outcomes to past events (in
episodic counterfactual thought); the ability to remember past events
can then be explained as a byproduct of the ability to imagine future
or counterfactual events. In line with these accounts, it has been
suggested that future-oriented mental time travel may contribute to
reducing delay discounting (Boyer 2008). It has also been suggested
that the early human cognitive niche may have involved selection for a
capacity for anticipatory planning
(Osvath & Gardenfors
2005), a suggestion that resonates with views that link mental time
travel to other cognitive capacities, such as language, that appear to
be unique to humans (Corballis 2011; Ferretti & Cosentino 2013;
Suddendorf 2013).



Future-oriented and counterfactual accounts, like past-oriented
accounts, are plausible as far as the function of what-where-when
memory is concerned but do not identify a function that could be
performed only when what-where-when information is accompanied by
autonoetic consciousness. In contrast to these accounts,
*metacognitive* accounts focus specifically on autonoesis,
suggesting that this form of consciousness may play a metacognitive
role. One possibility here is that autonoesis itself directly grounds
a sense of subjective certainty that an apparently remembered event
really happened, enabling the subject to act on remembered information
rather than floundering in uncertainty (Klein 2014; Tulving 1985a).
Another possibility is that autonoesis serves as one of several
criteria exploited by metacognitive monitoring processes that enable
the subject to tell whether he is remembering or imagining. A related
possibility is that autonoesis enables the subject
to take epistemic responsibility for his assertions about the past,
thus ultimately playing a communicative role (Mahr & Csibra
forthcoming). While these metacognitive accounts remain speculative,
they at least begin to approach the function of autonoetic episodic
memory.


## 4. Mnemicity



Assuming that a criterion of episodicity can be identified, it remains
to identify a criterion of mnemicity--a criterion that
distinguishes between remembering and imagining.


### 4.1 Remembering and imagining



The question of how to distinguish between remembering and imagining
is importantly ambiguous. On the one hand, we sometimes remember but
do so in a way that is in some sense inadequate; in such cases, we
naturally say that we are "only
imagining". The question
can thus be taken to concern the distinction between cases in which
the subject remembers successfully and cases in which he remembers
*unsuccessfully*. On the other hand, we sometimes think about
the past in a way that does not amount to remembering at all; in such
cases, too, we naturally say that we are
"only imagining".
A criterion of mnemicity must therefore distinguish both between
successful and unsuccessful remembering and and between remembering,
whether successful or unsuccessful, and *mere imagining*.


#### 4.1.1 Unsuccessful remembering



Distinguishing between successful and unsuccessful remembering
requires identifying the difference between cases in which the memory
process results in a genuine memory and cases in which it instead
results a memory error such as *confabulation* (Hirstein 2009).
The question of how to distinguish successful remembering from
unsuccessful remembering resulting in memory errors is central to the
theories of remembering discussed below, but philosophers have also
begun to investigate memory errors in their own right. Some have
considered the relationship between mnemonic confabulation and other
forms of confabulation (Bortolotti & Cox 2009; Hirstein 2005).
Others have asked whether confabulation and other memory errors might
not, counterintuitively, have beneficial effects. Fernandez
(2015b), for example, has argued that even wholly confabulated
memories may sometimes have adaptive benefits (but see Otgaar, Howe,
Clark, Wang, & Merckelbach 2015), while Michaelian (2013) has
argued that the misinformation effect, in which inaccurate information
concerning an experienced event is incorporated into the
subject's memory of the event (Loftus 1996), can, under certain
circumstances, have epistemic benefits (but see Shanton (2011)). And
others have attempted to understand the relationships among memory
errors of different types. Robins (2016a, a), for example, has
explored the relationships among successful remembering,
confabulating, and *misremembering*, characterizing remembering
as involving both an accurate representation of an event and retention
of information from experience of the event, confabulating as
involving an inaccurate representation and no retention of
information, and misremembering as involving an inaccurate
representation and retention of information. Robins'
account is discussed in more detail below.


#### 4.1.2 Mere imagining



Distinguishing between remembering and mere imagining requires
identifying one or more *memory markers*, where a memory marker
is a factor that discriminates between remembering, whether successful
or unsuccessful, and mere imagining. The concept of a memory marker is
itself importantly ambiguous. On the one hand, memory markers might be
understood as factors that the rememberer himself can employ, from the
*first-person* perspective, to discriminate between remembering
and imagining. On the other hand, they might be understood as factors
to which the theorist of memory can appeal, from a
*third-person* perspective, to discriminate between remembering
and imagining.



It is important to note that there is no guarantee of any
correspondence between first-person and third-person memory markers.
Many factors which might plausibly be held to shape the
rememberer's subjective judgements about whether he is
remembering or merely imagining--such as the vividness of an
apparent memory--are such that they do not track the objective
boundary between memory and imagination. And many factors which might
plausibly be held to track that boundary--such as the existence
of a causal connection between an apparent memory of an event and the
subject's original experience of
it--are such that they are
inaccessible to the rememberer and therefore ineligible to serve as
first-person markers. Criticisms of proposed memory markers that
disregard the distinction between first-person and third-person
markers may miss their target. Bernecker (2008), for example, objects
to the source monitoring framework in psychology (Johnson (1997); see
below), along with similar earlier approaches in philosophy (Smith
2013), on the ground that the markers identified by the framework
discriminate between memory and imagination only imperfectly. If these
approaches are understood as pertaining to third-person markers, then
Bernecker's criticism is telling. If, however, they are
understood as pertaining to first-person markers, then it is not:
since subjects' judgements about whether they are remembering or
imagining are sometimes mistaken, an account of first-person memory
markers should not identify markers that discriminate perfectly
between memory and imagination.



First-person memory markers play a vital role in enabling rememberers
to cope with two problems posed by the interaction between memory and
imagination. The *source problem*, arises
because subjects remember not only information deriving from
experience but also information deriving from a variety of other
sources, including imagination. For example, one might imagine an
event and later remember the imagined event. Hence, when one
remembers, one is faced with the problem of determining whether the
information that one remembers derives from experience or, rather,
from another source. Subjects appear to cope with this problem by
relying on a form of metamemory known as "source
monitoring" (Johnson 1997), in which they employ a variety of
content-based markers to determine whether or not they are remembering
on the basis of experience. For example, memories deriving from
experience tend to be more detailed and to include no information
about the cognitive operations that produced them, whereas memories
deriving from imagination tend to be less detailed and to include
information about the cognitive operations that produced them.



The *process problem*, in contrast, arises because subjects
engage not only in episodic remembering but also in episodic future
thinking and episodic counterfactual thinking and because (as we will
see) these forms of episodic imagining closely resemble remembering.
For example, one might imagine a future event or a counterfactual
event by drawing on information deriving from similar past events.
Hence, when one engages in episodic thought, one is faced with the
problem of determining whether one is remembering a past event or
imagining a future or counterfactual event. Subjects may cope with
this problem by relying on a form of metamemory which might be called
"process monitoring"; whereas source
monitoring relies primarily on content-based markers, process
monitoring may rely additionally on phenomenological markers, such as
the feelings of familiarity and pastness discussed above, and formal
markers, such as the subject's intention to remember or imagine
(Hoerl 2014; Urmson 1967).


### 4.2 Theories of remembering



A full theory of remembering will thus include an account of
first-person memory markers, but the theories of remembering described
here are concerned primarily with third-person markers. These theories
can be positioned with respect to two general--and arguably
incompatible--conceptions of memory. The conceptions in question
have been described in a number of different ways. Koriat and
Goldsmith (1996), oppose *storehouse* conceptions to
*correspondence* conceptions, while Robins (2016a) opposes
*archival* conceptions to *constructive* conceptions.
Borrowing some terminology from 
 epistemology, 
the conceptions in
question can also be described as *preservationist* and
*generationist*. Preservationism takes remembering to be
essentially a matter of encoding, storing, and retrieving information.
In philosophy, preservationism is reflected in
comparisons--beginning with Plato's wax tablet
metaphor--of memory to a variety of information storage
technologies (Depper 2016; Draaisma 2000). In psychology, it is
manifested in Ebbinghaus's ([1885] 1913) foundational
experimental work on memory for lists of nonsense syllables.
Ebbinghaus's legacy is carried on in a productive research
tradition, but the accent in contemporary psychology is on generative
conceptions of memory. Generationism takes remembering to be an active
process in which the subject constructs a more or less adequate
representation of the past. In psychology, generationism is manifested
in Bartlett's ([1932] 1995; Wagoner 2017) pioneering work on the
ways in which memories are created and recreated by the remembering
subject. In philosophy, many researchers continue to operate with a
preservative conception of memory, but, beginning with a growing
interest in false and recovered memories (S. Campbell 2003, 2014;
Hacking 1995; Hamilton 1998), generationism has become increasingly
influential.



Sufficiently moderate versions of preservationism and generationism
may not be incompatible. In order to account for deviations from
perfect storage, preservationists may acknowledge the active,
constructive character of remembering. And, since stored information
provides the raw materials out of which the subject constructs
representations of the past, generationists need not deny that
remembering involves storage of information. Less moderate versions of
preservationism and generationism, however, may be incompatible. Some
preservationists deny that genuine remembering is consistent with the
inclusion in the retrieved memory representation of content that goes
beyond the content that was included in the subject's original
experience of the event (e.g., Bernecker (2010)). Some generationists,
meanwhile, grant that remembering involves the preservation of
information originating in experience but deny that genuine
remembering requires the inclusion in the retrieved memory
representation of any content that was included in the subject's
original experience of the event (e.g., Michaelian 2016c). It is
difficult to see how these more extreme preservationist and
generationist conceptions might be reconciled with each other.



The preservationist conception is reflected in the *empiricist*
theory, which was influential in the first half of the twentieth
century and is thus the natural starting point for a review of
theories of remembering. The most influential theories in the second
half of the twentieth century were the *epistemic* theory and
the *causal* theory, which likewise reflect the preservationist
conception, with the causal theory gradually eclipsing the epistemic
theory. In the early years of the twenty-first century, the causal
theory has been challenged by new *simulation* theories, which
adopt a thoroughly generationist conception of memory. The remainder
of this section reviews each of these theories in turn.


#### 4.2.1 The empiricist theory



Empiricists see both memory and imagination as drawing on preserved
sense impressions. Identifying a marker for the distinction between
memory and mere imagination is therefore central to the empiricist
theory of remembering, and Hume ([1739] 2011) suggested two such
markers. First, he suggested that memory and imagination may be
distinguished by the latter's higher degree of flexibility:
memory respects the order and form of the subject's original
impressions, whereas imagination does not. This suggestion appears to
be unworkable. Hume himself acknowledged that degree of flexibility
cannot be employed as a first-person memory marker, since the subject
has no means of comparing a current apparent memory to an earlier
sense impression. And degree of flexibility fares no better as a
third-person memory marker, unless a very extreme form of
preservationism is assumed. Generationists, who conceive of
remembering as an active, constructive process, are bound to reject a
view of memory on which it is characterized by inflexibility. Moderate
preservationists likewise acknowledge that remembering is often highly
flexible; for example, they may acknowledge that one can remember the
elements of an event in an order other than that in which one
experienced them (Bernecker 2008).



Second, Hume suggested that memory and imagination may be
distinguished by the former's higher degree of
vivacity. As Pears (1990) points out, Hume's
notion of vivacity is ambiguous. It sometimes seems to refer to a
property of the representation produced by the apparent memory
process; the idea here would be that representations produced
by remembering are more detailed than representations
produced by imagining. But it sometimes seems to refer
to a property of the apparent memory process itself; the idea here
would be that remembering imposes itself on the subject in a more
spontaneous manner than does imagining. On either interpretation,
vivacity may have merit as a first-person memory marker, but it is
unworkable as a third-person marker. The representations produced by
remembering may be more detailed on average than the representations
produced by imagining, but only on average: imagination sometimes
produces representations containing a great deal of detail, and memory
sometimes produces representations containing very little detail.
Similarly, the process of remembering may on average occur
spontaneously more often than the process of imagining, but only on
average: we sometimes remember deliberately, and we
sometimes--as in the familiar phenomenon
of mind-wandering (Dorsch 2015)--imagine
spontaneously.



Due to these and other problems--see Holland (1954) for a
detailed discussion of the empiricist theory, versions of which he
attributes to Russell (1921) and Broad (1925), in addition to
Hume--the empiricist theory has few contemporary defenders. One
exception is Byrne (2010), who endorses a *neoempiricist*
theory which sees the content of memory and the content of imagination
as degraded and transformed versions of the content of perception. The
neoempiricist theory distinguishes between memory and imagination by
claiming that memory necessarily preserves cognitive contact with the
original event, whereas imagination may involve cognitive contact but
does not preserve it. Both aspects of this claim are problematic. The
claim that memory necessarily preserves cognitive contact may be
undermined by the generative character of remembering, at least if an
extreme form of generationism is assumed. And the claim that
imagination does not preserve cognitive contact is difficult to
reconcile with the fact that imagining draws on stored information.
Like the classical empiricist theory, moreover, the neoempiricist
theory fails to deal with both aspects of mnemicity, focusing
exclusively on the distinction between remembering and mere imagining
and saying little about the distinction between successful and
unsuccessful remembering. It may therefore not have a significant
advantage over the classical empiricist theory.


#### 4.2.2 The epistemic theory



Epistemic theorists (e.g., Ayer 1956; Annis 1980; A. Holland 1974; D.
Locke 1971; Munsat 1967; Naylor 1971; Ryle [1949] 2009; Zemach 1968)
see remembering something as being a matter of having known it
continuously since once first learned
 it.[1]
 The epistemic theory of remembering may capture important features of
our ordinary use of the verb
"to remember" (Moon 2013),
and it has found a number of contemporary advocates (e.g., T.
Williamson 2000; Adams 2011; Audi 2002), but it also faces a number of
serious problems. One problem is that, because the epistemic theory is
couched in terms of propositional knowledge, it applies to episodic
remembering only if we take episodic representations to be
propositional in character. Even if the theory is entertained as a
theory of semantic remembering, moreover, it remains problematic.
Semantic memory may correspond roughly to propositional memory, but
this correspondence is only rough: on most accounts, semantic memory
includes nonpropositional representations of various kinds. Thus the
theory applies at best to a subset of semantic memories.



Another problem is that, since knowledge requires truth,
justification, and belief, the epistemic theorist must claim that
memory requires truth, justification, and belief, and each of these
claims has been persuasively challenged. As we will see in
section 6, there appear to be cases of memory without
truth. There are likewise arguably cases of belief without justification
(Audi 1995; Bernecker 2011). Lackey (2005), for example, describes a
case in which, after initially forming a belief, the subject acquires
defeaters which undermine his justification for it. And there are arguably
cases of memory without belief. Martin and Deutscher (1966) illustrate one
kind of nonbelieved memory by means of the hypothetical case of a painter
who paints a scene that he takes to be imaginary but that turns out to
correspond exactly to a scene that he witnessed as a child;
intuitively, this is an instance of remembering without believing.
Since the subject lacks the phenomenology characteristic of
remembering, the epistemic theorist might in principle deny that this
particular case is an instance of remembering. But, in the kind of
nonbelieved memory studied by psychologists (Otgaar, Scoboria,
& Mazzoni 2014), the subject fails to form a belief
corresponding to his memory despite having the phenomenology
characteristic of remembering; the existence of nonbelieved memories of
this kind is well-established.



A further problem is that the theory appears either to collapse into
the causal theory or to make remembering into something quite
mysterious. As Deutscher (1989) points out, there would seem to be no
plausible story about what it is to retain knowledge that does not
appeal to the sort of causal connection posited by the causal theory.
Thus, if the epistemic theorist explicates retention of knowledge in
terms of causal connection, then his theory collapses into the causal
theory, and, if the epistemic theorist refuses to explicate retention
of knowledge in terms of causal connection, then his theory fails to
provide any real insight into the nature of remembering.


#### 4.2.3 The causal theory



Causal theorists see remembering as being characterized by the
existence of an appropriate causal connection between an apparent
memory and the subject's original experience of the remembered
event. The idea that a causal connection is essential to remembering
was unpopular when Martin and Deutscher published their influential
(1966) paper, but, despite early opposition (e.g., Squires 1969; Shope
1973; Zemach 1983), it has now largely eclipsed the epistemic theory.
Bernecker--who cites von Leyden (1961), Goldman (1967), Shoemaker
(1970), Anscombe (1981), and Armstrong (1987) as predecessors, in
addition to Martin and Deutscher--has recently developed and
defended it at length (Bernecker 2008, 2010). Not all contemporary
philosophers of memory explicitly endorse the causal theory, and some
suggest amendments or additions to it, but there are few who
explicitly reject the theory (Debus 2017). The idea that remembering
is characterized by an appropriate causal connection has thus taken on
the status of philosophical common sense.



The core of the causal theory is the claim that an appropriate causal
connection between the subject's apparent memory and his
original experience is both necessary and, along with relatively
uncontroversial additional conditions, sufficient for remembering.
There are two aspects to this claim. First, the claim that remembering
requires *a causal connection* already classifies certain cases
of apparent memory as merely apparent. For example, Martin and
Deutscher describe a case in which a subject experiences an event,
forgets it entirely, and later is coincidentally implanted with a
"memory" exactly
matching his original experience. The requirement of a causal
connection rules this case out as a case of
genuine memory. Second, the claim that remembering requires an
*appropriate* causal connection classifies certain further
cases of apparent memory as merely apparent. Martin and Deutscher
describe a case in which a subject experiences an event, describes it
to someone, forgets it entirely, is told about it by the person to
whom he described it, forgets being told, and then seems to remember
the event on the basis of what he was told. Here, there is a causal
connection, but intuitively it is of the wrong sort to sustain
remembering. Martin and Deutscher's suggestion
is that what is missing is a *memory trace*: simplifying somewhat,
the idea is that the subject's experience must
give rise to a stored representation which exists continuously in the
interval between experiencing and remembering and which contributes to
the production of the retrieved representation. The requirement of an
appropriate causal connection, where an appropriate causal connection is
one that goes continuously via a memory trace in this manner, rules this
case out as a case of genuine memory.



While the causal theory has been and continues to be enormously
influential, both the necessity and the sufficiency of the appropriate
causation condition have been questioned. Challenges to the
sufficiency of the condition have been more popular. One such
challenge appeals to the *epistemic relevance* of memory. Debus
(2010) argues that genuine memories are necessarily epistemically
relevant to the remembering subject, in the sense that he is disposed
to take them into account when forming judgements about the past. In
the most straightforward case, the subject remembers a given event and
therefore forms a belief that the event occurred. In less
straightforward cases, the subject may refrain from forming a belief
that the event occurred but nonetheless be disposed to do so. Because
it does not treat epistemic relevance as necessary for remembering,
Debus argues, the causal theory is bound to classify certain cases as
instances of genuine memory when in fact they are instances of merely
apparent memory. For example, in the case of the painter described
above, the painter disregards his apparent memory when forming
judgements about the past, and therefore it should not be classified
as a genuine memory; but the apparent memory is, we may assume,
appropriately caused by the painter's past experience, and
therefore the causal theory is bound to classify it as a genuine
memory. Given that epistemic relevance is necessary for genuine
memory, this argument suggests that the appropriate causation
condition must be supplemented with a condition explicitly requiring
epistemic relevance. The view that epistemic relevance is necessary
for genuine memory, however, may conflate mnemicity and episodicity:
one natural take on the case of the painter is that the painter is
remembering but, because he lacks autonoetic consciousness, not
remembering episodically.



Another challenge appeals to the nature of memory traces. Traces are
discussed in more detail below, but two main conceptions of traces are
available in the literature, with some theorists understanding traces
as *local*, individually stored entities with explicit content,
while others understand them as *distributed*,
superpositionally stored entities with implicit content. The local
conception, adopted by Martin and Deutscher (1966), is more
straightforward, but the distributed conception, inspired by
connectionist approaches to memory
(McClelland & Rumelhart 1986)
and developed in detail by Sutton (1998), has gradually become the
dominant view (Robins 2017). If the distributed conception is right,
then individual experiences do not, strictly speaking, result in
enduring individual traces but, instead, modify connection weights in
networks of event features. Robins (2016b) has argued that, for this
reason, a causal theory relying on distributed representations lacks
any means of singling an individual event out as the one that is
remembered. This would be an unfortunate implication, but the
distributed conception may be able to avoid it. On standard
distributed connectionist approaches (O'Brien 1991),
transient activation patterns are discrete explicit representations, even
though they are generated from information stored only holistically in
connection weights: thus at retrieval, there can be a distinct
representation of an individual remembered event.



Alternatively, the causal theorist might retreat to a local conception
of traces, but doing so might not enable him to avoid this difficulty.
Any causal theorist who acknowledges the constructive character of
remembering must acknowledge that, when one remembers, while some of
the content of the retrieved representation presumably originates in
one's experience of the remembered event, the
remainder may originate in one's experience of
other events. This implies that one may satisfy the appropriate causation
condition with respect not only to the remembered event but also with
respect to the other events in question. Given that one does not remember
the other events, satisfaction of the appropriate causation condition cannot
be sufficient for remembering. Overall, it is unclear whether the
appropriate causation condition is sufficient for remembering,
regardless of whether a distributed conception or a local conception
of traces is adopted.



If the appropriate causation condition merely fails to be sufficient
for remembering, an adequate theory of remembering might in principle
be produced by supplementing it with additional conditions, producing
a variant of the classical causal theory. If the condition fails to be
necessary, however, the causal theory will have to be rejected
outright, and, while challenges to the sufficiency of the condition
have been more popular, the necessity of the condition has also been
challenged. Such challenges are motivated by a tension between the
causal theory and the constructive character of remembering. The
classical version of the causal theory treats the content of a
retrieved memory representation as deriving entirely from the
subject's original experience of the remembered event. Causal
theorists do not require that the content of a retrieved
representation exactly match that of the corresponding experience. In
particular, they do not require that the retrieved representation
inherit *all* of the content of the experience. But most do
require that the retrieved representation not incorporate content
*not* included in the original experience. Research on
*constructive memory*, however, demonstrates that the content
of the retrieved representation routinely differs from that of the
experience not only in that it does not include some information that
the latter does include but also in that it does include some
information that the latter does not include. For example, in cases of
boundary extension, the subject sees part of a scene but remembers
portions of it that were beyond his field of view (Hubbard, Hutchison,
& Courtney 2010). In general, remembering is not a reproductive
but a reconstructive process, in which components of previous
experiences are extracted and recombined in a flexible manner, often
resulting in representations that include content not included in the
corresponding experiences (Schacter & Addis 2007).



The constructive character of remembering poses a problem for the
sufficiency of the appropriate causation condition, as we have seen,
but it also poses a problem for its necessity. In an attempt to render
the causal theory compatible with the findings of constructive memory
research, Michaelian (2011a) suggests modifying it so that it permits
the content of the retrieved representation to go beyond that of the
original experience, as long as two conditions are met: first, the
content of the retrieved representation must not go "too
far" beyond that of the experience; second, the memory
system must function reliably when it generates the new content. The first of
these conditions is problematically vague. Moreover, there appears to
be no way of drawing a meaningful boundary between cases in which the
content of the representation does not go too far beyond that of the
experience and cases in which it does. In some cases, a majority of
the content may derive from the experience. In some cases, only a
minority of the content may derive from the experience. As long as
part of the content was included in the experience, the causal
theorist can in principle classify the representation as a genuine
memory. In some cases, however, none of the content at all may derive
from the experience. Once the fraction of the content that was
included in the experience drops to zero, the causal theorist is bound
to classify the representation as a merely apparent memory. Given the
reconstructive character of remembering, however, such cases are bound
to occur, and it is not clear why the mere preservation of some
content, no matter how little, should make a qualitative difference
between genuine and merely apparent memory.



The second condition is likewise problematic. James (forthcoming)
argues that the introduction of a reliability condition tacitly turns
the causal theory into a causal-epistemic theory. The thought here is
that the only apparent motivation for imposing the condition is the
intuition that memory is a source of knowledge. This is unpersuasive,
as there is a clear difference, independent of any epistemological
considerations, between reliable and unreliable memory processes.
Confabulation, in particular, may be characterized by its
unreliability (Hirstein 2005). James also argues, however, that, once
a suitable epistemic condition--such as the reliability
condition--is added to the causal theory, the causal condition
itself becomes redundant. The thought here is that, if the reliability
condition is satisfied, then it should not matter whether the causal
condition is also satisfied. This is more persuasive, especially in
conjunction with the claim that there is no way of drawing a
meaningful boundary between cases in which the content does not go too
far beyond that of the experience and cases in which it does. Overall,
then, the modified version of the causal theory appears to be an
unstable halfway-point between the classical causal theory and a
theory which rejects the causal condition outright, replacing it with
a reliability condition. The simulation theory can, at least in some
versions, be understood as such a theory.


#### 4.2.4 The simulation theory



The idea that remembering the past is linked to imagining the future
may go back as far as Augustine (Manning, Cassel, &
Cassel 2013), but it has until recently played little role in the philosophy
of memory. It has, however, come to play an important role in the
psychology of memory, as psychologists have moved away from a
conception of episodic memory as what-where-when memory and towards a
conception of episodic remembering as a form of constructive mental
time travel. Reinforced by impressive brain imaging evidence and
extensive research on representational and phenomenological overlap
between remembering the past and imagining the future (Klein 2013;
Schacter et al. 2012; Szpunar 2010), this new conception emphasizes
the similarities between episodic memory, *episodic future
thought* (in which the subject imagines possible future events),
and, increasingly, processes such as *episodic counterfactual
thought* (in which the subject imagines alternatives to past
events). Taking the new conception to its logical conclusion, many
have suggested that, rather than distinct capacities for episodic
memory and episodic imagination, humans in fact have a single general
capacity for *mental time travel* (Suddendorf &
Corballis 2007). In psychology, this new conception has led to theoretical
frameworks such as the constructive episodic simulation approach
(Schacter, Addis, & Buckner 2008) and the scene
construction approach (Mullally & Maguire 2014), both
of which emphasize the simulational character of remembering. In philosophy,
it has led to simulation theories of remembering (Shanton &
Goldman 2010), which see remembering as a process of imagining past events,
a process in which a causal connection to the remembered event is at best
incidental.



Building on work on episodic future thought, Michaelian (2016c) treats
episodic memory and episodic future thought as processes carried out
by a common episodic construction system. Both processes draw on
stored information originating in experience of past
events--that is, on memory
traces--in order to construct representations of
events. Episodic future thought obviously cannot draw on traces
originating in experience of represented events, simply because the
relevant events have not yet occurred. Similarly, episodic memory does
not necessarily draw on traces originating in experience of
represented events: in some cases, it may do so, but the episodic
construction system, because it is supports both episodic memory and
episodic future thought, is not designed in such a manner that it
always does so. Michaelian's version of the
simulation theory, then, implies that an appropriate causal connection
is not a prerequisite for remembering. Building work on episodic counterfactual
thought, De Brigard (2014a) treats episodic memory as one function of
a system devoted to the construction of possible past
events--not only events that actually occurred but
also events that might have occurred but did not. De
Brigard's version of the simulation
theory, too, would seem to imply that episodic memory may in some
cases draw on traces originating in experience of represented events
but that it does not always do so.



If the simulation theory is right, both of the aspects of mnemicity
identified above may require rethinking. Regarding the first aspect,
Robins (2016a) has argued that, whereas the causal theory can appeal
to the existence of an appropriate causal connection in order to
distinguish among successful remembering, confabulating, and
misremembering, the simulation theory may not be able to accommodate
these distinctions, since it views both successful and unsuccessful
remembering as resulting from the same imaginative process. The
simulation theory can, however, appeal to the reliability of the
imaginative process in question, characterizing successful remembering
as involving reliable imagination resulting in an accurate
representation of the event, confabulation as involving unreliable
imagination resulting in an inaccurate representation, and
misremembering as involving reliable imagination resulting in an
inaccurate representation (Michaelian 2016b). This approach to memory
errors has the advantage of making room for *veridical
confabulation*, which can be characterized as involving unreliable
imagination resulting in an accurate representation,



Regarding the second aspect of mnemicity, the simulation theory
implies that the difference between memory and imagination is much
less dramatic than the traditional view takes it to be. Hopkins
(forthcoming) has described memory as imagination controlled by the
past. If the simulation theory is right, memory is indeed imagination,
but it need not be controlled by the past. One may merely imagine a
past event by imagining a counterfactual past event. But if one
imagines an actual past event, and if one's
imagination is reliable, then one is simply remembering it. There is, if the
simulation theory is right, no difference in kind between cases in
which one reliably imagines an actual past event at least in part on
the basis of one's experience of the event and cases
in which one reliably imagines an actual past event on another basis; in cases
of both sorts, as long as one's representation of the
event is accurate, one has a genuine memory of the event.



Philosophers committed to the traditional view of the difference
between memory and imagination are likely to object not only to this
implication of the simulation theory but also to the idea of mental
time travel itself. Research on mental time travel, as we have seen,
suggests that there is no qualitative difference between episodic
memory and episodic future thought. Adopting Perrin's (2016)
terminology, *continuists* argue explicitly that any difference
between them is merely quantitative, while *discontinuists*
grant that there are quantitative similarities between episodic memory
and episodic future thought but maintain that there are a variety of
qualitative differences between them. Discontinuism is the traditional
view. Debus (2014), for example, has drawn on relationalist accounts
of the objects of episodic memory (J. Campbell 2001; Debus 2008; see
section 5 below) to argue that, when one remembers
a past event, the remembered event itself may, due to
one's previous causal contact with it,
constitute part of the content of one's mental state,
whereas, when one imagines a future event, the imagined event cannot constitute
part of the content of one's mental state, because one
has had no causal contact with it. Perrin (2016), meanwhile, has argued that,
when one imagines a future event, one effectively stipulates the
identity of the subject whose experience one is imagining, so that
episodic future thought is immune to error through misidentification,
whereas, when one remembers a past event, the identity of the subject
is determined by one's causal relationship to
one's past experience, so that episodic memory
is not immune to error through misidentification. Others have argued
that episodic memory is itself immune to error through misidentification
(Hamilton 2009, 2013), but a more serious problem for these discontinuist
arguments is that they presuppose the causal theory of memory: since the
causal theory itself presupposes that there is a qualitative difference
between remembering and imagining, the arguments appear to beg the question
against the continuist view of mental time travel (Michaelian 2016a).



In addition to challenging the traditional view that there is a
qualitative metaphysical difference between memory and imagination,
the simulation theory challenges the view that there is a qualitative
epistemological difference between them. Philosophers have tended to
be dismiss the possibility of episodic knowledge of future events,
that is, of knowledge produced by imagining the future, as opposed to
the sort of semantic knowledge produced by prediction (Kneale 1971;
Swinburne 1966). The simulation theory, however, suggests that our
episodic knowledge of future events may be on a par with our episodic
knowledge of past events. This view is surprising, but it chimes with
recent work on imagination as a source of knowledge (Balcerak Jackson
forthcoming; Kind forthcoming).


## 5. Representation



Despite the disagreements among partisans of the theories of
remembering discussed in section 4,
they are, for the most part, in agreement on the point that
remembering involves representations of past events. The role of
representations in remembering, however, raises a number of difficult
questions of its own. One such question concerns the implications of
mental content externalism
for memory content in particular.[2]
Externalism, which has become the dominant view of the nature of
mental content, holds that the content of a subject's mental
representations depends not only on his own internal states but also
on his relationships to things in his external environment. For
example, what one thinks when one thinks the thought that one would
express by saying "water is wet"
is determined in part by the chemical composition of the substance that fills the
lakes and rivers and falls from the sky in the environment in which one learned
to use the word "water", namely,
H2O; had one learned to use the word
"water" in an environment in which
something other than H2O fills the lakes and rivers and
falls from the sky, then one's thought would have been that
that other substance is wet, not that H2O is wet (Putnam 1975).
This much is common ground among externalists. But a subject might
move from one environment to another, and externalists disagree about
the contents of memories formed before such moves and retrieved after
them. *Pastist externalists* (e.g., Boghossian 1989; Burge
1998) maintain that the past environment alone is relevant.
*Presentist externalists* (e.g., Ludlow 1995; Tye 1998)
maintain that the past and the present environments are both relevant.
And *futurist externalists* (e.g., Stoneham 2003; Jackman 2005)
maintain that the past, the present, and any future environments are
all relevant. Since the arguments for and against these views have had
little contact with mainstream philosophy of memory, they will not be
reviewed here; for further discussion, see Bernecker (2010).



Two further questions concerning the role of representations in
remembering have been at the heart of mainstream philosophy of memory.
These questions are sometimes run together, but they raise distinct
issues. The first, concerning retrieved representations, is the
question of the nature of *the objects of memory*. The second,
concerning stored representations, is the question of the existence
and role of *memory traces*.


### 5.1 The objects of memory



The direct objects of memory are those to which the subject is
related, in the first instance, when he
remembers.[3]
Historically, there have been two main competing views on the nature
of the objects of memory: *direct* realism and
*indirect* (or representative) realism.


#### 5.1.1 Direct realism



Direct realism (defended by Reid ([1764] 1997) and, more recently, by
Laird (1920)) claims that, when one remembers, one is in the first
instance related to past events themselves; it is thus perhaps the
most intuitively appealing view of the nature of the objects of
memory. The primary motivations for direct realism about the objects
of memory parallel the motivations for direct realism about the
objects of perception. One motivation is the thought that positing
representations that stand as intermediaries between the remembering
subject and the remembered object may have sceptical implications for
our ability to know the past. Another motivation is the thought that
remembering is phenomenologically direct, that is, that, in
remembering, we attend to past events, not to internal representations
of past events. The work on metamemory discussed in
section 4 suggests that remembering may in fact
often be phenomenologically indirect rather than phenomenologically
direct. But there are more serious problems for direct realism, and
it is these that provide the primary motivation for indirect realism.


#### 5.1.2 Indirect realism



Indirect realism (defended by J. Locke ([1689] 1998), Hume ([1739]
2011), and, more recently, B. Russell (1921)) claims that, when one
remembers, one is in the first instance related to internal
representations of past events. Here, again, the dialectic parallels
that of the debate between direct and indirect realists about the
objects of perception. In the domain of perception,
the argument from
hallucination takes the possibility of the occurrence of hallucinations
indistinguishable from successful perceptions to suggest that
hallucination and successful perception have something in common,
namely, an internal representation of a scene, and that it is to this
that the subject is related in the first instance in both cases. In
the domain of memory, the argument from memory
hallucination--or,
as it would more aptly be called, the argument from
confabulation--appeals to the possibility of
the occurrence of confabulations indistinguishable from successful
memories to suggest that confabulation and successful memory have in
common an internal representation of a past event and that it is to
this that the subject is related in the first instance in both cases.
Denying that representations are the direct objects of the relevant
mental states, moreover, leads to *disjunctivism*, according to which
perception or memory, on the one hand, and hallucination or
confabulation, on the other hand, are states of fundamentally
different kinds. Some have been prepared to defend disjunctivism about
memory (Debus 2008), but the cognitive processes at work in memory and
confabulation are highly similar, making disjunctive an unattractive
option from any broadly naturalistic standpoint.


#### 5.1.3 Compromise and hybrid views



Direct realism nevertheless retains its intuitive appeal, and some
have therefore advocated a compromise between it and indirect realism.
Bernecker (2008), for example, argues for the compatibility of the
causal theory of memory--most versions of which
treat memory as involving representations--and
direct realism about the objects of memory on the ground that
remembering a past event may require having a suitable representation
of the event without requiring that one be aware of the representation.
A compromise view of this sort may provide a response to the argument
from confabulation, since it acknowledges a role for representations
in both successful memory and confabulation. But it does not by
itself provide a response to a distinct problem, the
*cotemporality* problem. The cotemporality problem arises
because, while direct realism claims that the direct object of a
present memory is a past event, there is no obvious sense in which a
subject now might be directly related to a past event. Bernecker
(2008) argues that the cotemporality problem can be avoided if we
assume that past events continue to exist even after they have
occurred. This may, however, be a high metaphysical price to
pay simply in order to respect direct realist intuitions.



Even if concerns about the metaphysical price of
Bernecker's view are set aside,
there remain concerns about whether the view achieves a genuine
compromise between direct and indirect realism.
Since the view acknowledges that representations play an indispensable
role in remembering, it remains, at bottom, representationalist in
character. The recent philosophy of perception literature, however,
suggests the possibility of a view of the objects of memory which
incorporates elements of both representationalism and relationalism.
In that literature, the focus is on the character of perceptual
experience, with relationalists arguing that what determines a
subject's perceptual experience is an external
scene, while representationalists argue that what determines it is an
internal representation. This focus on perceptual experience opens up the
possibility of hybrid views, according to which perceptual experience
is partly determined by external scenes and partly determined by
internal representations (e.g., Schellenberg 2014). At present, the
prospects for hybrid views of memory remain unexplored.


### 5.2 Memory traces



In addition to retrieved representations, most theories see
remembering as involving stored traces. Both the *existence*
and the precise *role* of traces have, however, been matters of
controversy.


#### 5.2.1 The existence of traces



Opposition to including references to traces in a philosophical theory
of remembering often stems from particular conceptions of the nature
of philosophical, as opposed to scientific, theories. Thus some have
argued that philosophical theories of remembering should not posit
traces on the ground that philosophical theories are or should be
concerned with the nature of remembering as such, or perhaps with the
concept of memory, whereas traces pertain to the mechanisms that, as a
matter of contingent fact, underwrite the process of remembering (D.
Locke 1971). One response to this argument maintains that the nature
of remembering cannot be understood without understanding the
mechanisms that underwrite the process of remembering (Sutton 1998).
Another response maintains, more strongly, that traces may be part of
the very concept of remembering (De Brigard 2014b; C.B.
Martin & Deutscher 1966).



Others have argued that philosophical theories of remembering should
not posit memory traces on the ground that philosophical theories
ought not to dictate to scientific theories and that traces belong to
the province of the latter (Zemach 1983). One response to this
argument advocates a retreat to a purely logical conception of memory
traces, devoid of any empirical detail (Heil 1978; D.A. Rosen 1975).
Another response advocates the development of a conception of traces
based on current scientific theories of remembering (Sutton 1998).
This response, in turn, motivates the distributed conception of traces
introduced in section 4. As we have seen, the
distributed conception is not without its disadvantages; in particular,
it may have troubling implications for the causal theory. But it has
advantages as well; in particular, it may ground a response to
Wittgensteinian (1980; see also Malcolm [1963] 1975)
antirepresentationalist arguments, which often presuppose a local
conception of traces (Sutton 2015).


#### 5.2.2 The role of traces



Assuming that the existence of traces is granted, a full account of
remembering will have to describe the relationship between traces, the
representations produced by retrieval, and the representations
involved in perceptual experience.



De Brigard (2014b) reviews several positions that have historically
been defended regarding the relationship between traces and perceptual
representations. *Semidirect representationalism* holds that
perception is indirect and that traces are the same as the
representations involved in perception. *Indirect
representationalism* holds that perception is indirect and that
traces are distinct from the representations involved in perception.
As De Brigard emphasizes, what ultimately matters here is
relationships among contents rather than vehicles. He thus
distinguishes between *content invariantism*, which holds that
the content of the trace is the same as that of the perceptual
representation, and *content variantism*, which holds that the
content of the trace may differ from that of the perceptual
representation. In practice, since the invariantist/variantist
distinction cuts across the semidirect/indirect distinction, which
concerns relationships among vehicles rather than contents, semidirect
and indirect representationalism can often be grouped together.
*Direct representationalism* holds that perception is direct
and that traces are created after perception occurs. Extending De
Brigard's nomenclature, *direct relationalism*
would hold that perception is direct and that remembering does not involve
traces.



De Brigard's approach does not explicitly take the
relationship between traces and retrieved representations into account, and
taking this relationship into account expands the range of possible
positions. As before, perception might be held either to be direct or
to be indirect. If perception is direct, storage might be held either
not to involve traces or to involve traces. If storage does not
involve traces, retrieval might be held to be either direct or
indirect. The former possibility corresponds to a straightforward
version of direct relationalism. The latter possibility, on which
neither perception nor storage involves representations but on which
retrieval does involve representations, would be difficult to
motivate, as it is difficult to see from where the content of
retrieved representations might come if it is not supplied by memory
traces. If storage does involve traces, retrieval might, again, be
held to be either direct or indirect. The former possibility, on which
neither perception nor retrieval involves representations but on which
storage does involve representations, would be difficult to motivate,
as it is difficult to see what role traces might play given that they
do not contribute to retrieval. The latter possibility is the natural
way of understanding direct representationalism.



If perception is indirect, storage might be held either not to involve
traces or to involve traces. If storage does not involve traces,
retrieval might be held to be either direct or indirect. The former
possibility, on which perception involves representations but neither
storage nor retrieval involves representations, would be difficult to
motivate, as the considerations that motivate relationalism about
memory likewise motivate relationalism about perception. The latter
possibility, on which perception and retrieval involve representations
but storage does not, corresponds roughly to a view advocated by
Vosgerau (2010); on this view, storage may in a sense involve traces,
but stored traces, due to their inactive character, cannot be said to
have content. If storage does involve traces, retrieval might be held
to be either direct or indirect. The former possibility, on which
perception and storage involve representations but retrieval does not,
would be difficult to motivate, as, again, the considerations that
motivate relationalism about memory likewise motivate relationalism
about perception. The latter possibility is the natural way of
understanding both semidirect representationalism and indirect
representationalism.



Taking the relationship between traces and retrieved representations
into account also complicates the distinction between content
invariantism and content variantism. De Brigard applies the
distinction to the relationship between the contents of perceptual
representations and the contents of traces. It may also be applied to
the relationship between the contents of traces and the contents of
retrieved representations. But what ultimately matters here is the
relationship between the contents of perceptual representations and
the contents of retrieved representations. One is a content
invariantist with respect to this relationship if one holds that the
content of the retrieved representation is the same as the content of
the perceptual representation, and one is a content variantist if one
holds that the content of the retrieved representation may differ from
the content of the perceptual representation. Any view on which both
perception and retrieval involve
representations--including semidirect
representationalism, indirect representationalism, and something like
Vosgerau's view--may be
combined with either content invariantism or content variantism.



Philosophers have often treated remembering as a basically
preservative process, but this should not be taken to suggest that
content invariantism is the standard view in philosophy. While there
have been attempts to identify purely preservative forms of memory
(Dokic 2001), most philosophical theories of remembering allow for two
kinds of variance between the content of retrieved representations and
the content of perceptual representations. First, all theories allow
for the subtraction of content through forgetting. Second, many
theories allow for the addition of self-reflexive, second-order
content of the sort described in section 3. Thus
content variantism is in fact the standard view. Note, however,
that the standard form of content variantism permits the addition of
second-order content concerning the subject's
relationship to the remembered event but forbids the addition of
first-order content concerning the event itself. Most theories of
remembering thus remain preservationist in spirit. Another possible
form of content variantism permits the addition of both second-order
content and first-order content. Generationist theories of remembering
entail this more radical form of content variantism.


## 6. Accuracy



Generationist forms of content variantism raise the question of
accuracy in memory in an especially vivid way: if the content of the
retrieved representation can differ from that of the trace, which can
in turn differ from that of the perceptual
representation--or if,
as the simulation theory claims, there need be no trace linking the
retrieved representation and the perceptual
representation--there
would seem to be no guarantee that memory provides us with accurate
representations of past events. Generationist forms of content
variantism do not, however, guarantee inaccuracy, and preservationist
forms of content variantism do not guarantee accuracy, for the
accuracy of memory has two distinct dimensions.


### 6.1 Truth and authenticity



Adopting Bernecker's (2010) terminology,
*authenticity* refers to the correspondence between the
memory representation and the subject's
experience of the past event, while *truth*
refers to the correspondence between the memory representation and the
past event itself. Crucially, neither sort of accuracy entails the
other. A retrieved representation may be authentic, but, if the
subject misperceived the relevant event, it may nevertheless not be
true. A retrieved representation may be true, but, if the subject
misperceived the relevant event, or if he accurately perceived an
aspect of it other than what is given to him by the retrieved
representation, it may nevertheless not be authentic.



Thus, while preservative forms of content variantism imply that
genuine memories are always authentic, such memories are not always
true. Authenticity implies truth only where the subject's
original experience itself was accurate with respect to the
experienced event. Cases of misperception, again, illustrate the
possibility of authenticity without truth. Preservationists who wish
to hold that genuine memories are always true must therefore impose
this as an additional requirement, above and beyond what is required
by the core of their theory. By the same token, while generative forms
of content variantism allow that genuine memories are sometimes
inauthentic, such memories are not always false. Inauthenticity
implies falsity only where the subject's
original experience was both accurate and complete. Cases of boundary
extension (discussed above) or field-observer perspective switching
(Debus 2007b; McCarroll 2017; Sutton 2010b) illustrate the possibility of
inauthenticity without falsity. In cases of perspective switching, the
subject perceives an event from one perspective (field perspective)
but remembers it from another, perhaps even seeing himself in the
scene (observer perspective); while many or most observer memories are
inauthentic (since they fail to correspond to the subject's
original experience), they are not necessarily false (since they may
correspond to what an observer would have seen). For these reasons,
generationists do not hold that genuine memories are always authentic.
But those who wish to hold that genuine memories are always true can
impose this as an additional requirement


### 6.2 Factivity



To impose this additional requirement is to claim that memory is
*factive*, in the sense that genuine memories are necessarily
true, that is, that apparent memories that are not true are
*merely* apparent. In philosophy, the view that memory is
factive has been common. The standard arguments for the factivity of
memory are linguistic, appealing to the apparent incoherence of
asserting both that one remembers an event and that the event did not
occur (Bernecker 2017; cf.
Moore's paradox).
 Assessing these arguments is beyond the scope of this entry, but note
that they are controversial even among those who give linguistic
arguments a great deal of weight (De Brigard 2017; Hazlett 2010).
Among naturalists, who often give linguistic arguments less weight,
they are more controversial still. From a naturalistic point of view,
the goal of a theory of remembering ought to be to describe the
process of remembering itself, regardless of whether we are
intuitively inclined to classify its results as genuine or merely
apparent memories. If the same process may be responsible both for
producing true memories and for producing false memories, then an
adequate theory of remembering will not require that genuine memories
are always true--in the terms introduced in
section 2, the relevant natural kind may include both
true and false memories, regardless of whether our ordinary linguistic
practice permits us to group them together.



In psychology, the view that memory is factive has been much less
common. This is not very surprising, given that much psychological
research on remembering focuses on unsuccessful remembering:
understanding how unsuccessful remembering occurs provides important
insights into the mechanisms responsible for successful remembering,
just as understanding how perceptual illusions and hallucinations
occur provides important insights into the mechanisms response for
successful perception. What is more surprising is that psychologists
have sometimes gone too far in the opposite direction, assuming that,
because remembering is constructive, it is bound to be false (Ost
& Costall 2002). This is in effect to treat memory as
*counterfactive*. The distinction between authenticity and
truth enables us to see that constructive, generative remembering need
not be characterized by falsity. The generative character of
remembering does, however, point to the need for a more sophisticated
criterion of truth (S. Campbell 2014). While the fact that remembering
is generative does not imply that memories are bound to be outright
false, it does suggest that they are frequently false in some
respects. This, in turn, suggests that remembering need not be fully
accurate in order to be fully adequate, thus pointing towards a need
for a criterion that acknowledges that truth in memory comes in
degrees.


## 7. The Self



The question of truth in memory derives much of its importance from
the role played by memory in relation to the self. It is something of
a cliche to observe that memory makes us who
we are, but memory is indeed intimately linked to the self.


### 7.1 Personal identity



Locke ([1689] 1998)--who was perhaps anticipated in this by
Spinoza (Lin 2005)--discussed the idea that what makes a person
at a given time count as the same person as a person at an earlier
time is that he remembers the earlier person's experiences. This
*memory theory of personal identity*
 has been much discussed since Locke (Mathews, Bok, & Rabins
2009), and there are well-known substantive and methodological
problems for it. The primary substantive problem is that the memory
criterion for personal identity appears to be uninformative, because
one can by definition remember only one's own experiences, not
those of anyone else--if memory thus presupposes personal
identity, it is unenlightening to say that personal identity
presupposes memory. There have been attempts to meet this objection by
introducing the notion of *quasi-memory*, which is meant to be
like the notion of memory without the implication of personal identity
(Buford 2009; Parfit 1984; Roache 2006; Shoemaker 1970). While the
notion of quasi-memory may enable us to disentangle memory from
personal identity, it remains to be seen whether it is empirically
defensible (Northoff 2000).



The primary methodological problem is that arguments for and against
the memory criterion tend to rely on thought experiments involving
memory swapping and other such cases. Moving away from these far-out
cases, some philosophers have preferred to consider the implications
of real memory disorders. Craver (2012; cf. Craver, Kwan, Steindam,
& Rosenbaum 2014), for example, has argued on
the basis of cases of episodic amnesia such as that of the well known
patient KC (Rosenbaum et al. 2005) that memory is not a presupposition of
selfhood. Others have preferred to build on cognitive psychological
theories of autobiographical memory. Schechtman (1994, 2011), for
example, has argued that memory does not and need not provide simple
connections between discrete past and present moments of
consciousness, maintaining that what matters, as far as the sense of
personal identity is concerned, is the way in which autobiographical
memory summarizes, constructs, interprets, and condenses distinct
moments from the personal past to produce a coherent overall narrative
(cf. Goldie 2012). Approaches such as Schechtman's appear to
involve a change of subject, from *personal identity* as such
to the subject's *sense* of personal identity. This shift
is explicit in Klein and Nichols' (2012) examination of the role
of autonoesis in underwriting the sense of personal identity--the
sense that one now is the same person as someone at an earlier time.
Roache (2016) has questioned Klein and Nichols' interpretation
of the clinical case on which their argument depends, and the debate
over the relationship between autonoesis and the sense of personal
identity is ongoing (Fernandez forthcoming; Klein 2016b).


### 7.2 Autobiographical memory



Such approaches also appear to involve a second change of subject,
from *episodic* memory to *autobiographical* memory. The
extent to which this actually constitutes a change of subject is
debatable, for the relationship between episodic and autobiographical
memory is itself a matter of debate. Some philosophers have held that
all episodic memories are autobiographical (Hoerl 1999). In
developmental psychology, however, episodic memory, understood as a
capacity to remember particular events, is often treated as emerging
before autobiographical memory, which requires a capacity to organize
individual events into coherent narratives. Thus, autobiographical
memory is usually understood as including more than episodic memory.
Conway and Pleydell-Pearce's (2000; cf. Conway 2005)
influential view, for example, sees autobiographical memory as emerging from what
they refer to as the *self-memory system*, including an
autobiographical knowledge base containing information about specific
events, general events, and broader life periods. Accounts of
*personal semantic memory* go further, describing a form of
memory for one's past that is distinct from both episodic and
semantic memory (Renoult, Davidson, Palombo, Moscovitch, & Levine
2012). Views emphasizing *narrativity* are also influential
(Hutto 2017); rather than seeing autobiographical memory in terms of
stored information, Brockmeier (2015), for example, sees
autobiographical remembering as a process in which autobiographical
memories themselves emerge through the subject's active
construction of a life narrative. Interestingly, Cosentino (2011) has
argued that the linguistic capacity at work in the construction of
life narratives itself depends on the capacity for mental time travel,
including episodic memory.


#### 7.2.1 Rilkean memory



There is thus a need for work devoted to clarifying the concept of
autobiographical memory. In addition to clarifying the relationship
between autobiographical memory and episodic memory, such work might
also take more exotic forms of autobiographical memory into account.
Rowlands (2015, 2016), for example, has recently introduced the
concept of *Rilkean memory*. Rilkean memory, as Rowlands
defines it, is a type of autobiographical memory that is neither
episodic nor semantic. Episodic and semantic memories have content,
but Rowlands maintains that these are sometimes transformed into
something else which, while lacking content, is nevertheless
recognizable as a form of autobiographical memory. These Rilkean
memories can be either embodied or affective. Embodied Rilkean
memories manifest themselves in the form of bodily and behavioural
dispositions, such as when a runner adopts a certain posture due to
past injuries. Affective Rilkean memories manifest themselves when one
has certain feelings or moods in response to certain stimuli due to
certain past experiences, without being able to bring any information
about those experiences to mind.


#### 7.2.2 Memory and emotion



Though Rilkean memory clearly bears some relationship to recognized
forms of memory, it is, as Rowlands himself acknowledges, not entirely
clear whether it ultimately merits the name
"memory". The
concept of Rilkean memory does, however, foreground the role of
affect, including emotion, in autobiographical remembering. The
relationship between memory and emotion is complex and multifaceted
(see de Sousa 2017), but two issues in particular stand out. First, we
routinely experience emotions when we remember. These emotions may be
understood as themselves being memories, namely, memories of past
emotions, or they may be understood as being present emotions directed
at past events. Debus (2007a) argues for the latter possibility, but,
even if she is right, we do presumably sometimes have memories of past
emotions. This, in turn, raises the question of whether remembered
emotions are themselves emotions, as well as the question of how we
are to understand present emotions directed at remembered past
emotions.



Second, certain emotions, such as *nostalgia*, are necessarily
past-directed. Such intrinsically past-directed emotions raise
interesting questions. Howard (2012), for example, argues that
nostalgia can arise in connection with memories that are known to the
rememberer to be nonveridical. This implies that a version of
the paradox of fiction--the
challenge of explaining how an audience can feel something in
relation to an event they know to be fictional--arises for
memory. It also raises the question of whether nostalgia felt in
connection with memories that are known to the rememberer to be
nonveridical is necessarily inappropriate or whether it can under some
circumstances be appropriate.


## 8. Beyond Individual Memory



While most research on the metaphysics of memory has assumed that
remembering is something done by individuals on their own, this
assumption has recently been challenged, as researchers have drawn on
accounts of cognition as distributed or extended to interrogate the
role of *external memory* and on ideas from the burgeoning
interdisciplinary field of memory studies to investigate the
possibility of more or less robustly *collective* forms of
memory.


### 8.1 External memory



A distinction is sometimes drawn between *distributed* and
*extended* accounts of cognition, with the former referring to
a line of research in cognitive science that focuses on cognition in
complex sociotechnical systems consisting of multiple human and
technological components (Hutchins 1995) and the latter to a current
in philosophy of mind that focuses on cognition in systems centred on
human subjects augmented by technological or sometimes social
resources (Clark & Chalmers 1998). Accounts of
both sorts are committed to the rejection of traditional
"intracranialist"
views of cognition and their replacement with the
"extracranialist"
view that cognition sometimes exceeds the bounds of the individual brain,
and the difference between them may thus be merely one of emphasis, as
distributed cognition theorists emphasize remembering in sociotechnical
systems, while extended cognition theorists emphasize remembering in
technologically-augmented individuals. Thus Hutchins (1995) considers
how a cockpit--or rather the system consisting of the pilots of
an airliner plus various instruments--remembers its speeds, while
Clark and Chalmers focus on the case of Otto, a (hypothetical)
Alzheimer's patient who relies on a notebook to supplement his
unreliable memory. While both accounts are in agreement on the point
that external resources may count as memory stores only in the context
of larger systems, both confront us with the role of various forms of
external memory in human remembering.


#### 8.1.1 The concept of external memory



One question about external memory concerns the concept of external
memory itself. Clark and Chalmers' argument appeals to apparent
functional analogies between Otto's notebook and internal memory
in non-memory-impaired individuals, suggesting that, in virtue of
these analogies, appropriate external resources may, when certain
conditions are met, qualify as literal external memory stores.
Opposition to their argument has thus been driven by a variety of
apparent functional disanalogies between internal and external memory
(Adams & Aizawa 2008; Rupert 2009). External
memory, which tends to be designed to provide highly stable storage,
does not, for example, duplicate the constructive character of
internal memory. One response to these disanalogies is to retreat to a
more moderate alternative to extended cognition, such as embedded
(Rupert 2009), scaffolded (Arango-Munoz 2013; Sterelny 2010),
or situated (Sutton 2009) cognition, on which external resources may
play a vital role in remembering without themselves literally taking
part in the memory process. Another response is to move away from
*parity-based* arguments for extended cognition of the sort
offered by Clark and Chalmers to the *complementarity-based*
arguments advanced by Clark in subsequent work (e.g., Clark 2003).
While the former appeal to functional analogies between internal and
external memory, the latter appeal to functional disanalogies,
suggesting that external memory comes to play a role in remembering
precisely because it does not mimic internal memory (Sutton 2010a).
Given the constructive character of internal memory, for example,
stable forms of external memory may make a distinct and valuable
contribution to remembering.


#### 8.1.2 Cognitive consequences of new forms of external memory



Another question concerns the cognitive consequences of our growing
reliance on novel forms of external memory. Regardless of whether
external memory literally takes part in the memory process, our
reliance on such forms of external memory, particularly when they are
internet-connected, may have important cognitive consequences (Smart
2012). Some have worried that these are purely negative, with external
memory diminishing internal memory in one way or another (e.g., Carr
2010), but whether this in fact occurs is an empirical question. There
is some research suggesting that, when we know that information will
be available online, we tend to remember how to find that information,
rather than remembering the information itself (Sparrow, Liu,
& Wegner 2011). The consequences of our use of
web-connected forms of external memory have, however, only begun to be
studied, and it may be instructive here to recall that Plato already
voiced the worry that an older external memory technology, namely,
writing itself, would have a negative impact on our ability to remember,
a worry that most today would dismiss without a second thought.


### 8.2 Collective memory



In addition to the growing literature on the ways in which
technological resources contribute to remembering, there is a large
and dynamic literature on the ways in which groups remember together.
Or rather there are two distinct literatures here, one concerning
*small-scale* groups, the other concerning *large-scale*
groups. The former has been investigated primarily in psychology,
exemplified by studies of remembering in married couples (Harris,
Barnier, Sutton, & Keil 2014) or in mother-child dyads
(Reese, Haden, & Fivush 1993). The latter has been
investigated primarily in the social sciences and history, where, in what
has been termed a "memory boom"
(Blight 2009), an enormous amount of work on
how nations and similar entities remember their pasts has appeared in
recent years. One question of philosophical interest in this general
area is the relationship between memory in small-scale groups and
memory in large-scale groups. There is increasing interaction between
the two literatures (Bietti & Sutton 2015; Fagin,
Yamashiro, & Hirst 2013; Roediger
& Abel 2015), and it may turn out that
similar processes of remembering unfold in both small-scale and
large-scale groups. But small-scale and large-scale collective memory,
as we will see, do appear to raise somewhat different issues, and it
may turn out not to be a contingent matter that they have for the most
part been studied in different disciplines.


#### 8.2.1 Memory in small-scale groups



The central question concerning memory in small-scale groups is
perhaps whether such groups manifest *emergent*, robustly
collective forms of memory. A range of views on this question are
available (Barnier, Sutton, Harris, & Wilson 2008;
Wilson 2005), but the conservative view is certainly that, while remembering
may be affected by the social context in which it occurs, it is itself always
a strictly individual-level process. The conservative view is the
natural starting point, but there is a surprisingly good case to be
made for the radical view that remembering is sometimes a group-level
process. A promising place to look for robustly collective forms of
memory is in *transactive memory systems* (Wegner 1987):
stable, ongoing groups characterized by a division of responsibility
for remembering and a shared metacognitive awareness of that division
(Kirchhoff 2016; Theiner, Allen, & Goldstone 2010;
Tollefsen, Dale, & Paxton 2013). Drawing on
Wimsatt's (1986) notion of
emergence, for example, Theiner (2013) has provided a rigorous
argument for the view that transactive memory systems manifest a form
of emergent memory, in the sense that the group has a memory capacity
of its own, over and above those of its individual members. Drawing on
a somewhat different theoretical framework, Huebner (2013, 2016) has
developed a complementary approach. Thus, while the question remains
open, the conservative view may no longer be the obvious starting
point.


#### 8.2.2 Memory in large-scale groups



The central question concerning memory in large-scale groups is
whether such groups are capable of remembering in anything like the
sense in which individuals are capable of remembering. Applying
concepts developed in the domain of individual memory to the domain of
small-scale collective memory may already be problematic; applying
them to the domain of large-scale collective memory may be more
problematic still. Anastasio et al. (2012), for example, have argued
that the concept of *consolidation* (referring to the process
through which unstable, short-term memory representations are
transformed into stable, long-term memory representations) applies
both at the level of individuals and at the level of societies, but
this argument may overlook the disanalogies between internal and
external memory noted above. Similarly, Tanesini (forthcoming) has
argued that the concept of *amnesia* (referring to the
inability of an agent to retrieve memories that would normally be
retrievable) applies both at the level of individuals and at the level
of societies, but there is little evidence that patterns of
remembering and forgetting at the social level correspond particularly
closely to patterns at the individual level. Along the same general
lines, Szpunar and Szpunar (2016; cf. Merck, Topcu, &
Hirst (2016)) have argued that the concept of *episodic future
thought* (introduced above) applies both at the level of
individuals and at the level of societies, but it is unclear whether
societies are able to imagine their futures in ways analogous to those
in which individuals imagine their futures.



General concepts and theories developed in other areas of *social
ontology* have the potential to shed further light on collective
memory. For example, the literature on
collective intentionality
(Tollefsen 2006), may clarify the activity of joint reminiscing, which
might be understood as a form of joint attention to the past (Hoerl
& McCormack 2005; Seemann forthcoming).
By providing a novel test case, collective memory also
has the potential to shed light on general concepts and theories in
social ontology. For example, Smith (2014) has pointed out that,
whereas many social objects (institutions, contracts, and the like)
are continuants, in the sense that they endure over time, the speech
acts which, on many accounts, ground their existence, are events and
hence exist only at a given moment in time. It is unclear how events
might ground the existence of continuants, and one potential solution
to this problem is to ground the existence of social objects not in
speech acts but rather in forms of external memory, which are
themselves continuants (Ferraris [2010] 2013, 2015).


## 9. The Epistemology of Memory



In addition to their implications for the metaphysics of memory,
external and collective memory may have novel implications for
epistemology (Carter & Kallestrup 2016; Clark 2015;
Michaelian & Arango-Munoz
forthcoming). Most research on the epistemology of memory, however,
reflects the traditional concerns of individual epistemology, including
the viability with respect to memory knowledge of broad families of
epistemological theories, such as internalism and externalism (Madison 2017),
and of particular theories within those families, such as foundationalism
(Senor 1993), coherentism (Olsson & Shogenji 2004),
and reliabilism and virtue epistemology (Shanton 2011), as well as the
relevance to memory of issues such as scepticism (Baldwin 2001; Moon 2017)
and epistemic circularity (Alston 1986). Other research on the epistemology of
memory tackles concerns specific to memory. As Frise (2015, Other
Internet Resources) points out, there are unresolved debates over the
problem of forgotten evidence (Harman 1986), the problem of forgotten
defeat (A.I. Goldman 1999), and the problem of stored beliefs (Moon
2012). There are also ongoing debates over the alleged analogy between
testimony and memory (Barnett 2015; Dummett 1994)
and the question whether memory is a generative or a merely
preservative source of knowledge (Frise forthcoming; Lackey 2005;
Matthen 2010; Salvaggio forthcoming). Issues in the
epistemology of memory, of course, interact with issues in the
metaphysics of memory, but, as there is
a separate entry on the epistemology
of memory, these interactions will not be explored here in any detail.


## 10. The Ethics of Memory



The ethics of memory is a relatively new area, but research in this
area already concerns a number of distinct questions.


### 10.1 Memory and moral responsibility



The research on remembering as mental time travel introduced above
emphasizes the relationship between episodic memory and its
future-oriented counterpart, episodic future thought, and there are
potential links between mental time travel and *moral
responsibility*. Levy (2014; cf. Vierra 2016), for example, has
argued that deficits in episodic memory and episodic future thought in
psychopathy (Kennett & Matthews 2009; McIlwain 2010)
imply that psychopaths cannot genuinely intend to harm others and that they
therefore may not have full moral responsibility for their actions.
Craver et al. (2016), however, argue that subjects with deficits in
episodic memory and episodic future thought make moral judgements
similar to those made by normal subjects, suggesting that more work
needs to be done to establish a definitive link between mental time
travel and moral responsibility.


### 10.2 The duty to remember



Some researchers have argued that we may have a moral *duty to
remember*. Margalit (2002), for example, argues that we have a
duty to remember the victims of radical evil. Such an
obligation--which, as Blustein (2008) points out,
might hold either at the individual or the collective
level--would be consistent with the spirit behind
truth and reconciliation commissions and similar institutions (Neumann
& Thompson 2015). But the existence of a duty to
remember is controversial, with some maintaining that there is no general
duty to remember the past and even that there may in some cases be a duty
to forget (Rieff 2016).


### 10.3 The right to be forgotten



Our increasing reliance on novel forms of external memory, may have
surprising ethical ramifications. The default for human memory is to
forget, and most of the information that we encounter never makes its
way into long-term memory. The default for computer memory, in
contrast, is to remember, and researchers are beginning to explore the
ethical implications of moving from a state of affairs in which
forgetting is the norm, in the sense that one's
words and deeds would in general leave few permanent traces, to one in which
remembering is the norm, in the sense that many of our words and deeds
leave behind more or less permanent digital traces
(Mayer-Schonberger 2009). When remembering is the norm, people
may, in particular, be deprived of any opportunity for a fresh start
after engaging in inappropriate behaviours, leading some to argue for
a *right to be forgotten* (Ghezzi, Pereira, &
Vesnic-Alujevic 2014; J. Rosen 2012). From a legal and technological
point of view, such a right is likely to be difficult to implement.
From a moral point of view, a right to be forgotten may imply a duty
to forget, and it is unclear whether we can plausibly be held to have
such a duty (Matheson 2013).


### 10.4 The ethics of external memory



Novel external memory technologies may ultimately reshape the norms
governing individual remembering (Burkell 2016; O'Hara 2013),
but even in the short term there are pressing ethical questions
related to the impact of *external memory technologies* on
cognition and the self. Regarding cognition, some have, as noted in
section 8, voiced unease about the cognitive impact of increasingly
prevalent use of such technologies (Carr 2010). Others, however, are more
optimistic (Bell & Gemmell 2009), and assessing the empirical
evidence for optimistic and pessimistic claims about the cognitive
impact of external memory technologies is no easy matter (Heersmink
2016; Loh & Kanai 2016). Regarding the self, Heersmink (2015,
forthcoming) has argued that an extended mind perspective implies that there are
strict ethical constraints against interfering with individuals'
external memories (cf. N. Levy 2007). Clowes (2013, 2015), however,
has raised the possibility that the fact that internet-connected forms
of external memory are often strongly influenced by agents other than
the individuals to whom they belong means that they do not count as
parts of the relevant individuals' minds.


### 10.5 The ethics of memory modification and enhancement



With the emergence of new techniques for altering the functioning of
memory systems--for example, retrieval of a stored memory results
in a period of reconsolidation during which the retrieved memory is
labile and susceptible to modification, potentially allowing
interventions to alter traumatic memories (Spiers & Bendor
2014)--ethical questions concerning various forms of *memory
modification* have become more pressing (Erler 2011; Hui &
Fisher 2015; N. Levy 2012; Liao & Wasserman 2007). Liao and
Sandberg (2008) identify a number of questions raised by memory
modification technologies; in light of the close relationship between
memory and the self noted above, it is no surprise that many of these
concern the effects of memory modification on the self. Modifying
someone's memories may, for example, limit his self-knowledge by
depriving him of opportunities to learn about his own actions or erode
his sense of agency by depriving him of the possibility of viewing
himself as an agent with respect to events in which he was involved.
Nevertheless, Liao and Sandberg argue that, in certain cases, the
benefits of memory modification may outweigh its costs, so that there
need be no general ethical barrier to the use of emerging memory
modification technologies. Much of the debate so far has focussed on
the suppression of traumatic or otherwise undesirable memories, but
parallel questions are raised by the use of novel methods for the
*enhancement* of memory abilities by pharmaceutical and other
means (Bostrom & Sandberg 2009). Critics of the memory
enhancement debate, however, have argued that the evidence for the efficacy of
the relevant methods is mixed (Zohny 2015) or that the debate often
overlooks important differences among kinds of memory (Fox, Fitz,
& Reiner forthcoming).