## 1. Background




Moritz Schlick is primarily remembered as the leader of the Vienna
Circle of Logical Positivists, which flourished in the early
1930s. Few philosophers of science today would deny that
their views have been influenced - one way or the other - by the
positions which emerged from the group of philosophers, mathematicians,
and social scientists who gathered in between-wars Vienna. And
while it cannot be denied that other Circle members were more prominent
and influential over the long-term, none contributed more unity and
cohesion to the Vienna group during its brief existence. Indeed,
long before 1930, when the Circle's Manifesto,
"*Wissenschaftliche Weltauffassung: Der Wiener
Kreis*", appeared, Schlick had already made contributions to
scientific epistemology which exerted a profound influence on
subsequent generations of philosophers (Neurath 1973, Ch. 9). And while
other Circle members quite deservedly continue to receive a great deal
of attention, there has always been a steady interest in
Schlick's views on a range of issues, for there is much of
lasting value to be discovered in them. 




Schlick was born in Berlin in 1882 and grew up as the son of a
middle-class factory manager. After *gymnasium*, he
attended the University of Berlin, intent from the start to study
physics. His ambition led him to work with Max Planck and he
received his Ph.D. in 1904. After a year of experimental work at
Gottingen, he eventually made his way to Zurich where he took up
the study of Philosophy. In 1910, he secured a position at
Rostock, moving on to Kiel before assuming the Chair of
*Naturphilosophie* at Vienna in 1922. Through all these
changes, as well as subsequent modifications of his thought, the
evidence of Schlick's training in Berlin remained just below the
surface. Schlick was, after all, the heir apparent to the
tradition of philosophical physicists, a tradition founded by Hermann
von Helmholtz, the icon of 19th Century physics and an influential
leader of the *zuruck zu Kant* movement, and continued by
his student and (later) colleague Planck (Coffa 1991, 179-183). 
Although few professional philosophers embraced the methods and
problems of the philosophical physicists, they were highly influential
throughout the community of professional physicists, largely due to
their prestige.


## 2. The Philosophical Physicists: Helmholtz and Planck




Although Schlick was originally trained in Physics, it is important
to remember that, in late 19th Century Germany, physicists
were deeply interested in philosophical issues, especially at
Berlin. Schlick was the intellectual heir of both
 Hermann von Helmholtz,
a major figure among 19th Century physicists and a
champion of the *zuruck zu Kant* movement and Max
Planck. In 1889, Planck succeeded Gustav Kirchhoff and became
Helmholtz' colleague. Both Helmholtz and Planck integrated
Kantian themes in their philosophical thinking and there can be no
doubt that, even though Schlick could never be considered much of a
Kantian, he was deeply sympathetic with many of Kant's
ideas. To begin with, Kant's interests in epistemological
concerns arising from the advanced mathematical sciences attracted
Schlick's admiration and respect, much as it had drawn the
interests of Helmholtz and Planck. And all three embraced the
goal of developing a philosophical understanding of recent developments
in physical science in the spirit, if not the letter, of Kant's
thought. For the most part, their departures from Kant's
original doctrines may be viewed as innovations or improvements of
Kant's insights, introduced without abandoning their own most
fundamental philosophical commitments. 




For instance, one of Helmholtz' most well-known innovations is
the study of perception in his monumental *Handbook of Physiological
Optics* (1856-1867) (Helmholtz 1924-5). This work was the
source of his so-called 'sign-theory', based on the idea
that perceptions are signs or place-holders for what they signify, but
do not resemble or copy them in any way. In his early writings,
Helmholtz thought sensations are signs of their external causes, so the
associations among sensations represent corresponding regularities
among their sources. Consequently, it is the regular changes of
signs, their serial structure, which reflects the order of their
underlying causes. But this latter consequence implies a causal
theory of perception which is fundamentally antithetical to
Kant's understanding of causality. After all, Kant had
restricted the operations of causality to the realm of appearances,
thus excluding unobservable causes lying behind and causing observable
phenomena. But this departure from a basic tenet of Kant's
thought was compounded by the fact that Helmholtz' account of the
knowledge of the location of objects in space is thoroughly empiricist,
and also rests on the principle of causality, understood as a causal
realist would. But in his 1881 notes to his memoir, Helmholtz
corrected himself, recalling that Kant's views on causality were
limited to lawfulness among appearances (Friedman 2010, 631; Friedman
1997, 30-1). What Helmholtz then asserted, in his classic essay
"On the Facts of Perception," is that the inference to a
hypostasized reality lying behind the appearances goes beyond what is
warranted by the lawfulness obtaining among appearances. Indeed,
all localizations of objects in space are really nothing more than the
discovery of the lawfulness of the connections obtaining among our
motions and our perceptions. The difference between what is
genuinely perceived and its realistic interpretation is just the
difference between the regularities in our perceptions and the
hypothesis of enduring, substantial sources of the perceived
regularities (Helmholtz 1977, 138-140). 




Although Helmholtz' philosophical work was not particularly
well-received by professional philosophers like
 Hermann Cohen,
co-founder of the Marburg School of neo-Kantians, it exerted a powerful
influence on physicists (Cohen 1885, 202-204). In particular, Max
Planck was an early supporter of the sign-theory. But Planck
never interpreted the sign-theory causally, like Helmholtz had in his
earliest writings. Rather, Planck recognized that "our
perceptions provide, not a representation of the external world"
but, rather, "measurements furnish the physicist with a sign
which he must interpret" (Planck 1960, 53; Planck 1933,
84). Furthermore, Planck generalized the sign-theory, arguing that
it is not objects, in and of themselves, which are known, but the
structural relations in which they stand to one another. His
fundamental idea was that what is known are not the natures of
'things' but complex structures of relations connecting
'things' to one another (Planck 1933, 84ff. and 1960,
53). Thus, the 'objects of knowledge' are not objects
at all but, rather, what is known are the relata of the structural
networks of relations in which they stand to other relata. And,
as recent developments have increased the level of abstraction of
scientific thought, it has become further removed from its
anthropomorphic origins. So the unification of the scientific
world-picture is achieved through increasing abstraction which, in
turn, drives structural representation, thus reducing the
anthropomorphic elements in the scientific image of the
world (Planck 1949, 105). The result of
Planck's effort is a theory of knowledge which is structuralist,
generalized from Helmholtz' sign-theory of perception, but which
nonetheless preserves the themes of unification and objectivity derived
from Kant.




These themes are particularly evident in Planck's celebrated
(1908) Leiden lecture on "The Unity of the Physical
Universe", directed at Ernst Mach's phenomenalistic
*Naturphilosophie* (Planck 1960, 1-26). Without going into
details, Mach regarded physical objects as unnecessary
hypostasizations, implying that the mechanical view underlying physics
is little more than an elaborate myth. The physics of the matter
were effectively settled when Planck secured the mechanical foundations
of irreversibility in his Radiation Law of 1900 by relying on Ludwig
Boltzmann's statistical approach to thermodynamics which, in
turn, implied atomism. Yet it remained to establish the
philosophical implications of these achievements. In his Leiden
lecture, Planck argued that this result presented an objective
world-picture abstracted from its anthropomorphic origins to produce a
synthetically unified image of the world (Planck 1960, 6). Such a view, Planck argued, can
only be produced through the unification of the diverse fields of
physical phenomena if they are synthesized by means of mathematical
abstraction. Such abstraction generalizes the sign-theory to
apply to theoretical as well as perceptual representations, resulting
in a full-blown structuralist epistemology (Planck 1933, 84ff.; Planck
1949, 105). And it is this method of abstraction that
produces the synthetic unity grounding scientific objectivity. 
The result is that physical entities are 'objective', in
the Kantian sense, since they embody the lawfulness of
appearances. Indeed, Planck insisted that what is
'objective' is precisely what the heroes of the history of
science, from Copernicus to Faraday, would have regarded as
'real' (Planck 1970, 25-6). Despite the
strident Kantian themes of Planck's argument, his conclusion has
always been regarded as a particularly virulent form of convergent
realism (Stolzner 2010).


## 3. Early Epistemology




Emerging from the tradition of the philosophical physicists,
Schlick's early thought bears the marks of his intellectual
legacy. After the completion of his graduate study in physics,
Schlick soon turned his attention to philosophy (Schlick 2006a). 
Within a few short years he had written a youthfully enthusiastic
ethical tract in 1908, called *Lebensweisheit*, a lucid analysis
of concept-formation called "The Boundaries of Scientific and
Philosophical Concept-Formation" (1910), as well as a substantial
essay on "The Nature of Truth in Modern Logic" (1910)
(Schlick 2006b; Schlick 1979a, 25-40, 41-103). In "The
Boundaries...", Schlick provided a broad sketch of his
understanding of scientific thought, which identifies the aim of
science as the reduction of phenomena to relationships governed by law,
thus exhibiting individual events as special cases of universal,
exceptionless regularities. Science is expressed mathematically, in
spatio-temporal form to provide for exact measurement. And the
individual sciences are demarcated by distinctive intensive qualities,
as 'mass' distinguishes mechanics, 'heat'
thermodynamics, etc. Although the methods of mathematico-scientific
concept-formation reduces the entire natural world to purely
quantitative relations, it is powerless in the face of irreducible pure
qualities. This is the task of philosophy so that philosophy
becomes the *theory of qualities*. Schlick's work on
"The Nature of Truth in Modern Logic" not only provides a
broad survey of treatments of truth then current in German philosophy,
but it also introduces an original view of truth as univocal
designation. A judgment, as a structured complex of its
constituents, is coordinated with the fact which consists of the
entities signified by the judgment's constituents, arranged in a
way which is coordinated with the structure of the particular
judgment. When the constituents are structured in a judgment so
that the whole judgment univocally designates a situation in the world,
then the judgment is true; otherwise, it is false. The conception
of truth as univocal coordination figured prominently in
Schlick's pre-Positivist theory of knowledge.




The centerpiece of Schlick's early epistemology is a deep
cleavage between intuitive acquaintance and conceptual knowledge. 
Although Schlick's distinction is reminiscent of Kant's
contrast between intuitions and concepts, Schlick regarded intuition as
fully naturalized, much as Helmholtz had. When the elements of
judgments are initially identified, they are grasped qualitatively, as
sensory impressions, like the visual image of a particular dog or the
memory image of a horse. These intuitions of acquaintance
are spatially qualitative, since they are not only extended but
situated with respect to one another in the space of the particular
sensory modality through which they are perceived. They are also
temporal, since they succeed one another in time. For an example,
Schlick considered the visual image of something in the distance which,
as it approaches, is identified, first of all, as an animal, then it is
recognized as a dog and, when it comes close enough, it will be
recognized as my dog 'Fritz'. Each of these cases
involves the recognition of one thing - the image of that which is
approaching - as something else, an animal, a dog, and (finally)
Fritz. Thus, each of these cases involves knowledge that the
image is that of an instance of some class (Schlick 1979a, 119-121;
Schlick 2009, Sec. 2). And the same process, in which one thing is
recognized as another and therefore known, occurs in cases of
scientific knowledge. For instance, the early explanations of
light recognized that its behavior was much the same as the behavior of
waves. Thus, in the work of Christian Huyghens, light came to be
known as a wave phenomenon or, in other words, as the wave-like
propagation of a state. Later, through the work of Heinrich
Hertz, it was realized that light was unlike mechanical waves which
traveled through a medium (such as water or air) but, rather, light
behaved more like electrical waves. Accordingly, light became
known as an electromagnetic wave phenomenon. In this case, as in
the everyday case of the knowledge that the approaching animal is my
dog Fritz, light was originally known as a wave phenomenon and only
later did it become known as an undulatory disturbance in an
electromagnetic field (Schlick 1979a, 121-2; Schlick 2009, Sec.
3).




In the early stages of everyday knowing, what is re-discovered or
recognized when something is known is an intuitive idea. Intuitive
ideas present images which are signs of their contents and are drawn
from sensory experience. Of course, images are vague, blurred, and
ill-defined so that when one conjures up an image, say, of one's
father, the expression on his face may not be clear and distinct, so that it
may be impossible to tell whether he is frowning or merely looking
puzzled (Schlick 1979a, 126-7; Schlick 2009, Sec. 4). And while
intuitive ideas are sufficient for the purposes of everyday life,
scientific inquiry naturally demands more rigorous methods for
capturing and expressing ideas. For this reason, concepts -
ideas with precisely delineated contents - are used. And while
the meanings of terms used in everyday discourse are usually intuitive
ideas, in science they are almost exclusively concepts. This provides
scientific judgments with content which is accurately circumscribed,
while at the same time eliminating their intuitive content. In
his *General Theory of Knowledge* of 1918, Schlick explained
that concepts are formed in clusters, just as the primitive concepts
of a mathematical field are defined in terms of one another by the
axioms of the discipline. But in his earlier epistemological writings,
he explains concept-formation in a more traditional fashion, by
reference to marks or characteristics (*Merkmale*) which belong
to all the objects which fall under the concept. Concepts thus
represent classes of objects, defined in terms of determinate traits,
so that their scope is exactly demarcated. Thus they differ from
intuitions, which are indistinct representations of what is presented
to a particular sensory modality. So the intuition of a triangle in
general or a man in general can only be a hazy, fuzzy-edged visual
representation of some particular triangle or man. And while everyday
knowing proceeds by comparisons of intuitions, scientific knowledge
replaces intuitions in these comparisons with precisely delineated
concepts. In short, it is through its reliance on concepts that
scientific thinking takes knowledge to a higher level than everyday
knowing.




Thus, in his earliest philosophical writings Schlick introduced an
innovative conception of truth as univocal designation and affirmed a
contrast between intuitions and concepts which was ultimately derived
from Kant and naturalized by Helmholtz. Soon, Schlick was
presented with an opportunity to display his scientific acumen, by
explaining the philosophical import of Special Relativity.


## 4. Special Relativity




Schlick availed himself of the opportunity to elaborate his
epistemological views in application to the new physics of Relativity
in his 1915 essay on "The Philosophical Significance of the
Principle of Relativity" (1979a, 153-189). This essay
is particularly significant in Schlick's development since it
first presented certain philosophical tenets which would figure in all
his subsequent work. Implicit in the general philosophical scheme
in which Schlick discussed Relativity is an objective, logical
distinction between the representational framework in which scientific
claims may be formulated and those claims themselves. An
intrinsic function of the representational scheme is the constitution
of the very concepts in which the formulation of empirical claims is
first made possible. Moreover, since the same empirical claims
may be expressed in distinct representational schemes, the content
which is expressed by all the differing conceptual frameworks comprises
the common, objective content of scientific assertions. In
contrast, what varies from one description to another reflects the
features of the representational systems which distinguish them from
one another.




Schlick applied these insights to the fact that no physical means
suffice to distinguish inertial frames or, in other words, no (uniform,
rectilinear) motion can be detected relative to the ether. There
are two alternative responses to this situation. The first
alternative, due to Lorentz and Fitzgerald, accommodates experimental
findings through the postulation of compensating contractions of moving
bodies in the direction of motion. Buttressed by additional
auxiliary hypotheses, the Lorentz-Fitzgerald hypothesis preserves the
absolute space and time of Euclid and Newton, as well as Galilean
kinematics, while explicating experimental failures to detect the
absolute rest of the ether by positing a real effect of absolute motion
on length. The alternative presented by Einstein in the Special
Theory was simply to deny the presupposition of an absolute time
reference, allowing that two spatially separated events may be
temporally ordered in one way for a given system of reference and may
also be ordered differently for a distinct, yet equally legitimate
system. Contractions of length are then a consequence of the
relativity of reference frames: the length of a measuring rod depends
on its velocity for a given frame of reference (Schlick 1979a,
160-1). Consequently, the facts of observation are accommodated
equally well by the Principle of Special Relativity as they are by the
Lorentz-Fitzgerald hypotheses. In other words, they are
equivalent or "both theories do the same thing". 
(Schlick 1979a, 162) The principal advantage of Einstein's
approach is that his solution is clearly the simplest. At this
juncture, it should be noted that Schlick did not argue that the choice
between the available alternatives is conventional because they are
*empirically* equivalent, implying all the same observational
consequences. Rather, Schlick repeatedly urged that there is an
underlying *physical* equivalence from which the empirical or
observational equivalence follows. And the fact that it is the
physical rather than observational equivalence which serves as premise
of his argument is especially evident from his use of his earlier
analysis of the concept of truth to explicate the equivalence.




Schlick thought the situation in physics presented a thorough-going
analogy with Poincare's treatment of the conventionality
of geometry. Schlick noted, first of all, that
Poincare's geometric conventionalism was founded on the
Kantian insight that it is only the behavior of bodies in space that
forms the object of study, so that the resulting physics is "the
product of two factors, namely the spatial properties of bodies and
their physical properties in the narrower sense" (Schlick 1979a,
169; Cf. also 1979a, 230-233). The point of Schlick's
reference to Poincare is to illustrate the particular variety of
conventionalism operative in Poincare's treatment of
geometry, in order to apply it to the case of Special Relativity. 
And just as Poincare isolated two factors in the treatment of
the motion of rigid bodies, in general any true theory may be regarded
as the product of a reference-system, or representational scheme, and
the judgments formulated in that system. Since there are
alternative ways of securing univocal coordination, the components with
respect to which distinct but equivalent representations differ are
artifices of the representational scheme. Parting from
Poincare, Schlick recognized that the representational framework
that appears simplest when regarded in isolation may nonetheless
require excessively complicated formulations for the description of
reality. And he insisted - *contra*
Poincare - that it is the simplicity of these formulations that
is the most compelling desideratum, not the simplicity of the
representational scheme. Thus, the representational scheme that
allows for the simplest description of reality is always to be
preferred - so much the worse for Euclid, and Poincare,
too.


## 5. General Theory of Knowledge




Schlick's earlier epistemological insights, as well as the
conventionalist framework developed in his work on the Special Theory,
set the stage for his thought in the two works which distinguish his
pre-Positivist era: *General Theory of Knowledge* (largely
composed in 1916, with its first edition appearing in 1918 and the
second edition in 1925) and *Space and Time in Contemporary
Physics.* (Engler 2009, 130 fn. 51) (*Space
and Time ...* appeared for the first time in 1917 as an
extended essay in the prestigious journal, *Die
Naturwissenschaften;* soon it was re-issued in three more editions
and eventually translated into eleven languages). Before
explaining how Schlick's epistemology embraced the new physics,
it is necessary, first of all, to consider how he further developed his
earlier epistemological insights.



*General Theory* is notable for a key innovation in its
treatment of concepts, for they are defined in terms of mathematical
equations rather than reducing them to complexes of intuitive images
(Schlick 2009, Sec. 5). In order to articulate his ideas about the
nature of concepts and how they are formed, Schlick borrowed the idea
of definition by axioms from recent work in the foundations of geometry
by Moritz Pasch, David Hilbert, and Henri Poincare. In their
work on alternative geometries, these mathematicians came to regard the
effects of altering the axioms of geometry as changing the meaning of
their constituent terms, thus re-defining the primitive geometric
concepts. The idea is ingenious in its simplicity, for it treats
the geometric primitives as defined by the relations they bear to one
another according to the axioms, so the meanings of the terms
'point', 'lies between', and 'lies
upon' are fixed by the geometric axioms. The reason
mathematicians adopted this method is to insure the certainty of
geometry by insuring that it was invulnerable to the criticism that its
primitive elements were defined by intuition.




Schlick claimed the method of definition by axioms was implicit
because, unlike explicit definition, occurrences of the defined term
cannot necessarily be replaced by a combination of the expressions which define
it. And he praised the method for its specification of
meanings independently of any intuitive content. Implicitly
defined terms possess a clarity and precision of scope which cannot be
achieved by concepts defined by abstraction from
experience. Since, of course, axiomatic definitions
stipulate the meanings of all their constituent concepts in terms of
the remaining ones, the axioms effectively define concepts by their
relations to one another. Thus implicit definitions are
structural definitions, and their constituent terms are structurally
defined (Schlick 2009, Sec. 7). The concepts thus defined are
only related to the other elements of the axiom system and are not
related to anything external to the axiom system until the definition
is coordinated with extra-linguistic things. In Schlick's
earlier writings, he had stated that concepts themselves are functions
which signify or designate the items with which they are coordinated or
associated. Accordingly, even implicitly defined concepts must be
coordinated with objects, elements of the class of things to which it
applies (Schlick 1979a, 130; Schlick 2009, 23; Ryckman 1991,
Sec. 3). Of course, these objects, like the concepts which
designate them, are distinguished by possession of the properties in
terms of which the designating concepts are defined. Such
coordinations give empirical content to implicitly defined concepts,
transforming them into full-blooded concepts rather than empty
place-holders. Moreover, the concepts which dominate
scientific thought at any given stage of its development must be
modified, revised, and supplemented as science advances. Then a
conceptual characterization of a given phenomena which was used at an
earlier stage may not be at a later stage as, for instance, the
judgment 'A light-ray consists of a stream of moving
particles', drawn from Newtonian optics was later replaced by
'A light-ray consists of electromagnetic waves'. 




Schlick's new understanding of concept-formation allows him to
seriously address the question of how the respective intuitive spaces
of each of the senses are coordinated in the construction of a general
intuitive space, which is not specific to any particular sense
modality. The intuitive images of experience are spatially
ordered, since they exhibit relative locations as well as spatial
extension. In addition, since experiences occur one after
another, they also exhibit an intuitive temporal order. This
results in a distinct spatio-temporal ordering for each of the sense
modalities, so that an intuitive order of smells, as well as an
intuitive order of tastes (and so forth) are given in
experience. The first step in the advance from purely
subjective experiences to the transcendent reality of scientific
objects is to coordinate the spatio-temporal frameworks of the distinct
sense modalities. Thus, when a sore spot on one's leg is
touched by one's forefinger, the feeling of the touch is
accompanied by a visual image of the finger touching the leg. The
coincidence of these two separate and distinct types of sensory data
contributes evidence to the overall coordination of the spatio-temporal
orders of the different sense modalities. This is the
method of point-coincidences which Schlick applied to characterize the
advance to knowledge of the transcendent world from the purely
subjective domain of qualitative images. Of course, the idea of
point-coincidences also plays a central role in General Relativity and
it has generally been assumed that Schlick picked up the idea from his
work on the new physics. But recent scholarship has demonstrated
that, in fact, Schlick worked on the notion long before Einstein
published the General Theory and may well have been Einstein's
source of the notion (Engler 2009, 135ff). The important
point in the present context is that the coordination of a single
individual's sense modalities is but the first step in the
construction of the transcendent order. The next phase consists
of the coordination of point-coincidences among different
individuals. If an instructor wishes to draw attention to some
feature of a triangle on a blackboard at the front of a class, he
points to the feature, thus effecting a point-coincidence between the
tip of his finger and the feature of the triangle. And even
though everyone witnessing the demonstration has a different
perspective, what they all share is their observation of the
point-coincidence of finger-tip and the geometric feature. 
Further, it is to be noted that not every sensory point-coincidence is
an objective one and it is generally true that not every objective
point-coincidence is observed directly but is constructed or inferred
from ones that are. Finally, all measurements, all determinations
of space and time, are based on just such spatio-temporal
point-coincidences (Schlick 2009, Sec. 31).




Earlier Schlick had argued that knowledge consists in the
identification of that which is known with that as which it is known
or, in other words, knowledge consists in the relation of one
thing to some other thing, as which it is known. And this is only
achieved when one of the objects which is known is, in turn, related to
still others, as it is in the myriad spatio-temporal relations in which
it stands to other objects. Ultimately, all these relations can
be known quantitatively by specifying a number of magnitudes, thus
reducing the relations of the objective spatio-temporal order to
quantities. Of course, this cannot be achieved within the
qualitative order since the different relations of position and
temporal order are qualitatively different and cannot, for that very
reason, be compared. But the entities populating the objective
spatio-temporal order are wholly unlike the denizens of the subjective
realm which are the intuitive objects of experience, the immediately
given sensory data. Both may be univocally designated by
implicitly defined concepts and both kinds of entities are, therefore,
objects of possible knowledge. As such, intuitive contents are
attributed full reality and, in addition, the objects populating the
spatio-temporal order, the entities of advanced theoretical science,
are just as real as the contents of consciousness with which they are
correlated.




Schlick expended considerable effort discussing the differences between
intuitive acquaintance and conceptual knowledge, insisting that, even
though intuitive images are real, acquaintance with them does not
constitute knowledge. This thesis directly confronts the idea,
held by a number of philosophers, that acquaintance with intuitive
contents is, indeed, a species of knowledge which is more direct and
immediate than conceptual knowledge. By comparison, scientific
knowledge is regarded as a poor substitute, lacking the intimacy of
intuitive acquaintance. Two champions of this belief are
 Henri Bergson,
who
thought that direct access to intuitive contents could (somehow)
'unite' the knower with the object known, and
 Edmund Husserl,
who
proposed that a genuinely philosophical intuition could become the
basis of a kind of scientific cognition in which the subject is in
direct contact with its object, without any symbolism or mathematics,
any inferences or proofs (Bergson 1955; Husserl 1965). 
Bergson called this intimate perception of objects
'intuition' and Husserl called it
'*wesenschau*'. But the reason why intuition
can never constitute knowledge is, of course, quite obvious to
Schlick. On his view, knowledge requires two terms: that which is
known and that, as which, it is known. But intuition, considered
as an act of consciousness, involves only that which is intuited. 
In short, the attempt to identify intuition as a form of knowledge is
simply a conflation of knowledge with acquaintance, of unelaborated,
direct perception or sensation with conceptual knowledge, of
*kennen* with *erkennen* (Schlick 2009, Sec. 12).




Schlick's discussion of the differences between intuition and
knowledge laid the groundwork for his treatment of realism. He
cautioned, at the outset of his discussion, that the question of
realism is not a philosophical problem, but an everyday one. And
the view that guides the comings and goings of ordinary life is
naive realism, which assumes that reality consists simply of the
objects of sense perception. Of course, the demands of day-to-day
affairs seldom require any distinction between the perception of an
object and the object perceived, until one encounters an illusion which
demands the differentiation of, say, a mirage from a puddle or
pond. Only then is a representation first distinguished from its
object. It is at this point that the ordinary person realizes
that the mirage was real but that the pond or puddle was not. 
Thus refined, the naive criterion of reality is extended beyond
the reach of the senses once it is realized that, even when an object
is not perceived, its effects provide a sufficient condition of its
reality, as when a hunter finds a ravaged animal in the forest and
concludes that a predator is in the neighborhood. And it is in
precisely this way that naive realism is naturally extended to
include, not just perceptions themselves as well as the objects
perceived, but also the causal sources of observed effects. In
this way, naive realism naturally leads to classical causal
realism.




Then it simply becomes useful to refer to those objects which are not
given in sensory experience - or at least not presently given
- as 'things-in-themselves' since they are, by the
causal criterion, real. Things-in-themselves are just the transcendent
entities of the objective, three-dimensional world of everyday
material objects, as well as the unobservable, theoretical entities
postulated by contemporary science. Unsurprisingly, the reality of
these entities is contested by a variety of related views, which
Schlick classifies as 'immanence' philosophies. The most
prominent immanence view is the kind of phenomenalism found in
thinkers from John Stuart Mill to contemporaries like Joseph Petzoldt,
Ernst Mach, and (as Schlick added in the second edition of *General
Theory* ...), Bertrand Russell. More curious, perhaps, is
that Schlick also indicted his intellectual forebear, Hermann von
Helmholtz, as an immanence philosopher. Basically, these thinkers all
restrict reality to the given, so that reality consists exclusively of
colors, tastes, and smells, as well as other sensations, presented in
constantly changing combinations with one another. This is, of course,
just to deny the reality of transcendent objects, thus abjuring the
causal realism implicit in everyday and scientific talk of
transcendent objects which exist and endure beyond momentary
sensations. Instead, the immanence thinkers claim that all talk of
transcendent objects consists entirely of discourse about complexes of
sensations which exhibit more stability and constancy than
others. Mach stated the common view of immanence philosophies that
material bodies do not produce sensations, because bodies are, at
bottom, nothing more than complexes of sensations (Schlick 2009, Sec.
25). Of course, immanence views differ among themselves in their
efforts to identify which particular complexes of sensation are
identified with everyday material bodies and scientific entities,
especially when the latter are not perceived. 




The classic immanence view is one which identifies material bodies
with the combinations of sensations which would appear, in a given
situation, if a perceiver were present. Of course, this is just
John Stuart Mill's definition of bodies as 'permanent
possibilities of sensation' - a treatment which persists in
the writings of many of his followers, in one form or another. 
For instance, Bertrand Russell, in *Our Knowledge of the External
World*, calls the stable combinations 'aspects',
declaring that "Things are those series of aspects which obey the
laws of physics" (Russell 1922, 110). Specifically, Russell
argued that so-called 'ideal aspects' - ones which are
not presently perceived - may be logically constructed from those which
are. Their reality may then be readily assumed. But with
this assumption, any grounds of distinguishing between given aspects
and assumed ones vanishes, nor is there any means of recovering them,
without complicating the system beyond all recognition. Schlick
noted that, because of Russell's sheer audacity in pushing his
account to the limit, the result is not prone to the inconsistencies
which plague other accounts. Indeed, it is undeniable that
Russell's "bold position" is one of the most
successful efforts to carry out the immanence philosophy (Schlick
2009, 502). In a different vein, Joseph Petzoldt acknowledged that
*esse* is not the same as *percipi*, though he then
endeavored to identify the existence of objects with some limited group
of sensations, a different group for each perceiver. Despite the
countless problems this approach encountered, the critical point which
Petzoldt missed is simply that it is impossible to simply identify any
particular sensation or group of sensations with a material body,
without further conditions relating the sensation or sensations (as,
for instance, Russell provided) (Russell 1922, 106). And
that is because it is the lawful regularity among sensations which
warrants the collection of the series of changing sensations under a
single material body. Mach very nearly realized this when, in
*The Analysis of Sensation*, he abandoned Mill's
'possibilities' and replaced them with the mathematical
notion of a functional relation. But such a purely
mathematical idea can never be substituted for an empirically-based
concept of reality. Such efforts are, at bottom, attempts to
conceptually embody a law, as epitomized in Helmholtz' "The
Conservation of Force: A Memoir" (Kahl 1977, pp. 49-50). 
Specifically, Helmholtz identified the objective power of a law with
force, thus reducing the reality of material bodies and scientific
entities to a conceptual substitute. But concepts, according to
Schlick, can never possess the reality of the contents of consciousness
or transcendent things-in-themselves (Schlick 2009, Sec. 25). 


## 6. Relativity




In correspondence with Einstein, Schlick explained that his
monograph on *Space and Time in Contemporary Physics* was
"less a representation of the general theory itself than a
thorough-going elucidation of the thesis that space and time have now
forfeited all objectivity in physics" (Schlick 1917). Of
course, Schlick is referring to Einstein's remark in his 1916
paper on the General Theory, that the admission of arbitrary
coordinative transformations "removes the last vestige of
physical objectivity from space and time" (Einstein 1916,
117). In his monograph, Schlick first described the differences
between the space of the older physics and the space postulated by
Einstein. In Newtonian physics (as well as the physics of the
Special Theory), all measurement was founded on the notion of a rigid
rod and space was still regarded as Euclidean so long as measurements
were made within the same coordinate system. Thus, in the older
physics, space was conceived as complete with metrical properties,
defined by rigid rods which possess the same length in any place at any
time. It is particularly to be noted that the metrical properties
of space were regarded as independent of the distribution of bodies in
space and their gravitational fields. It is precisely these
conditions that are changed in General Relativity. Rather, in the
General Theory, the principle of general covariance implies that
properties cannot be ascribed to space independently of any
consideration of the things in it. Einstein showed that
non-Euclidean methods of determining measurements must be used in the
presence of a gravitational field and this follows from the insight
that it is the things in space which give it a particular structure.
The result is a complete relativization of space (Schlick 2006a, Sec.
VII). 




In classical mechanics, it was decided by convention (see above)
that a rigid rod was the same length throughout space and this
convention was modified in Special Relativity. But in General
Relativity, the length of a rigid rod may also depend on its place and
position in such a way that consistency with Special Relativity is
maintained. Thus, to maintain the general postulate of
relativity, it is necessary to reduce the objective spatial structure
of the earlier physics to a non-intuitive topology. This is a
radical departure from the objectivity of the spatial structure of
these earlier systems, which was entirely an artifact of their fixed
metrical structure. But in Relativity Theory, the resulting
conceptual construction admits of distinct metrical structures in
different regions depending on the gravitational field in that region.
As Schlick reflects in the closing pages of *Space and Time
...*, the very possibility of the objectivity of this
conceptual construction depends entirely on the method of
point-coincidences. Any features of the world-picture which do not
contribute to the systematization of point-coincidences are not
physically objective. And all world-pictures which contain laws
governing point-coincidences are thoroughly equivalent. 
Furthermore, since any functional, single-valued deformation of the
world-picture leaves all point-coincidences undisturbed, the equations
of physics retain their form under such transformations, implying that
they are covariant under all substitutions. These substitutions
also leave the form of physical equations unchanged for
coordinate-systems in motion, allowing for the relativity of space
within such coordinate-systems, thus depriving space and time of the
"last vestige of physical objectivity" (Schlick
2006a, Sec. VII). 




Einstein was so impressed with Schlick's presentation that, in
a letter to Arnold Sommerfeld, Einstein described it as
"masterly", perhaps because Schlick was one of the first
commentators to see that space and time have no existence or reality
prior to the metric field. 




Nor was it long before *Space and Time ...* was succeeded
by the first edition of Schlick's *General Theory of
Knowledge*. During the same period, Schlick spent a year
engaged in war work at Aldershof airport outside Berlin followed, in
1921, by an appointment at Kiel. Since rumors were already
spreading about a possible appointment at Vienna, Schlick's
family stayed in Rostock until 1922, when they moved to Vienna where he
assumed the Chair of *Naturphilosophie* which had previously
been occupied by Ernst Mach and Ludwig Boltzmann (v. d.
Velde-Schlick 2008; Ferrari 2009). Schlick's selection for
the post was probably initiated by the mathematician Hans Hahn and the
physicist Phillip Frank, with a strong recommendation from
Einstein. When Schlick arrived in Vienna, he immediately became
involved with Hahn and Frank, as well as the economist Otto Neurath, in
their Thursday night discussion meetings in the Chemistry Building of
the University of Vienna. Schlick was a welcome addition to the
group, and together they formed the core of what would later become
known as 'the Vienna Circle' (Uebel 2003). Philosophy
would never be the same.




However, before arriving in Vienna, Schlick engaged the
neo-Kantians,
 Hans Reichenbach
and
 Ernst Cassirer,
who had published their own philosophical understandings
of the new physics of Relativity. In his *Relativity Theory
and Apriori Knowledge* of 1920, Reichenbach had argued for a
modified conception of Kant's synthetic *apriori*, which
challenged Schlick's thought in a decisive way
(Reichenbach 1920). At Einstein's request, Schlick wrote to
Reichenbach in the Fall of 1920, hoping to air the differences between
them (Schlick 1920; Einstein 1920). In his own essays, Schlick had
challenged Kantian apriorism principally by identifying the
presuppositions of the new physics as conventions, in
Poincare's sense. Since the presuppositions of
Relativity were alien to classical physics, they were nothing like the
self-evident, eternal verities that comprised the Kantian
*apriori*. But while Schlick rejected Kant's treatment of
the *apriori* altogether, Reichenbach claimed to have preserved
its most important element, its constitutive function (Reichenbach
1920, Ch. V; Friedman 1999, 59-70; Oberdan 2009). For Kant had
attributed the *apriori* the far more philosophically
significant function of constituting the object of experience or
knowledge. Indeed, such principles are the general laws for ordering
experience to produce knowledge. Since all empirical knowledge
presupposes these ordering principles, they can never conflict with
experience and are, in this sense, necessarily true. (Reichenbach
1920, pp. 55-56) Schlick first wrote Reichenbach in the Fall of
1920, acknowledging that he regarded the assumption of constitutive
principles as self-evident; indeed, he feared that the matter was so
obvious that he might not have discussed it sufficiently in
his *General Theory of Knowledge* (Schlick 1920a, p. 1; Oberdan
1994, pp. 109-110). Nonetheless, it is precisely the principles
which Reichenbach himself had identified as synthetic
*apriori* that constitute an observation or measurement of an
experience. Yet, Schlick confessed, he was unable to discover
any characteristics of these alleged synthetic *apriori*
principles that genuinely distinguish them from conventions. Of
course, it then follows that the precepts Reichenbach called
"synthetic *apriori*" were just what Schlick had
identified as "conventions" and the differences between
them were, at most, terminological (Schlick 1920b, 2). But this
apparently terminological difference, Schlick thought, masked a far
deeper difference separating them since, on Reichenbach's
understanding, the *apriori* constitutes the objects of
experience and knowledge whereas, on Schlick's, conventions only
constitute concepts, which may be applied to experiences and objects,
but do not constitute them. Thus Schlick insisted on
distinguishing his own realist epistemology from Reichenbach's
modified Kantianism, because of the latter's implicit
anti-realism.




Schlick also contributed a critical essay on Ernst Cassirer's
1921 work on *Einstein's Theory of Relativity* to the
prestigious journal *Kant-Studien* (Cassirer 1921; Schlick
1979a, 322-334). In "Critical or Empiricist Interpretation
of Modern Physics?" of 1921, Schlick explained that
Cassirer's argument rested on a false dichotomy. On the one
hand, Cassirer's own Logical Idealism incorporates principles for
the ordering and measuring of sensations to constitute physical
objects. On the other hand, the only alternative Cassirer
considered is a variety of phenomenalistic empiricism founded on
"the *sensualistic* concept of experience". In
other words, Cassirer's operative assumption is simply that the
only possible philosophical frameworks for understanding contemporary
science are a strict empiricism or one incorporating constitutive
principles. Of course, Schlick regarded his own philosophical
framework as a clear counterexample, since it is an empiricist
epistemology distinguished by its inclusion of constitutive
principles. Thus, Cassirer committed the same error as
Reichenbach by blithely ignoring the possibility of constitutive
principles which are not synthetic *apriori* judgments.
 Naturally, a combination of empiricism with constitutive
principles would fall somewhere between the strict empiricism Cassirer
refutes and the Logical Idealism Cassirer defends. At this point,
Schlick first used what would eventually become a familiar complaint
against Kant and the neo-Kantians among Logical Positivists, especially
their characterization of the constitutive principles as synthetic
judgments *apriori*. As Schlick understood constitutive
principles, they are certainly not synthetic *apriori*
principles, for they are conventions, which are neither
*apriori* nor synthetic (Schlick 1979a, 322-334). The
result of Schlick's critique was, in Einstein's words,
"truly inspirational" (Einstein 1921).


## 7. Transition




Shortly after Schlick arrived in Vienna, he was invited by the
mathematician Hans Hahn to participate in a seminar on *Principia
Mathematica* by Alfred North Whitehead and Bertrand Russell. Upon
its conclusion, Schlick organized (at the request of his students,
Herbert Feigl and Friedrich Waismann) organized an extra-curricular
discussion group, which came to be called the 'Schlick
Circle' and (eventually) the 'Vienna Circle'. Their
first reading was
*Tractatus Logico-Philosophicus*, written by Russell's
student, Ludwig Wittgenstein (Wittgenstein 1961; Stadler 2001, Ch.
5). Soon, Schlick was writing Wittgenstein, seeking additional
copies of his work, telling him about the study group in Vienna, and
requesting personal meetings. After several failed attempts, Schlick
finally arranged with Wittgenstein's sister, Margarete
Wittgenstein Stonborough, to visit him in early 1927 (McGuinness 1967,
14). The first clear evidence that Schlick had (at last!) obtained
a copy of the Tractatus was in a letter to Einstein in June of 1927.
(Schlick 1927a) The following month, Schlick effusively described
the *Tractatus* as "the deepest" work of the new
philosophy (Schlick 1927b). Over the next few years, Schlick and
Wittgenstein met as time permitted, carrying on philosophical
discussions ranging over a broad array of topics, from the idea of
geometry as syntax, to verificationist and operationalist theories of
meaning, topics in logic and mathematics, and even solipsism.



Of course, the
discussions of verifiability in the late 1920s led to widespread
disputes in later positivist thought. But even in the early years,
Schlick and his students to wondered how ethical statements might be
verifiable. In *Problems of Ethics*, Schlick attempted to
interpret ethical statements as empirical claims about the means for
maximizing happiness. Relying on relative judgments of values, Schlick
argued that an empirical foundation of an ethical system based on
maximum happiness. On Schlick's account, happiness is not to be
construed superficially but as the elated sense of fulfillment that
accompanies actions carried out for their own sake. Hence, there are no
apriori moral statements fixing absolute moral values.




Wittgenstein dictated some of his thoughts to Schlick, including a
strident verificationist series of remarks, and shared several
manuscripts with Schlick as well, including (perhaps) his so-called
'Big Typescript' of 1932-1933 (Iven 2009,
Wittgenstein 2005). Several other documents survive the period,
particularly notes taken by Schlick's student, Friedrich
Waismann, when he accompanied Schlick on his visits to Wittgenstein
(McGuinness 1967). In addition, there were joint travels undertaken by
Wittgenstein and Schlick during the period of their interaction (Iven
2009; Stadler 2001, Ch. 6). The principal effect of this influence on
Schlick was the assimilation, into his already well-defined
philosophical views, of insights stimulated by these
conversations. 




 During the same
period, Rudolf Carnap joined the faculty of the University of Vienna as
well as the Schlick Zirkel. He brought a manuscript with him,
which he called "Konstitutionstheorie", and which was
eventually published, with Schlick's help, as The Logical
Structure of the World (Carnap 1928). Schlick even assisted
Carnap in locating a publisher for the work. It was at this time
that Schlick penned the essay "Experience, Cognition, and
Metaphysics" of 1926, which represents a particularly important
juncture in his thinking. Schlick attempted to link current
influences on his thought - Wittgenstein's Tractatus 
and Carnap's Aufbau - with his earlier ideas, especially the
distinction between intuitions and concepts (Schlick 2008, pp. 33-56;
Wittgenstein 1961; Carnap 1928; Schlick 2009, Sec. 7). 




Within a few years, Schlick wrote the essays which are characteristic
of his early Positivist thought. The first one, "The Turning
Point in Philosophy," appeared in 1930. It contains an early
version of the thesis that the function of philosophy is the analysis
of meaning (Schlick 1979b, 154-160). A more decisive article was the
1932 essay, "Positivism and Realism", a classic piece
which shaped some of the most characteristic philosophical work to
emerge from the Positivist tradition (Schlick 1979b, 259-284). Schlick
interprets the verifiability principle strictly, by spelling out
verification in terms of sensible experience, but at the same time
broadly, construed to admit any logically conceivable circumstances of
verification (like the future verification of mountains on the far
side of the moon). The basis of this principle, Schlick argues, is to
be found in scientific practice. He cites Einstein's analysis of
"simultaneity" in Special Relativity as his primary
example, an illustration which would become a staple of Positivist
lore. Schlick also mentioned Planck, who acknowledged that experience
was the source of scientific knowledge. Schlick called the
philosophical view founded on this principle, "Logical
Positivism", using the designation introduced by A. E. Blumberg
and Herbert Feigl (Blumberg and Feigl, 1931). As Schlick explained it,
Logical Positivism is essentially a realist epistemology, like the one
developed in Schlick's General Theory of Knowledge, which shares
little with the classical positivism of
 Auguste Comte,
 Ernst Mach,
and Hans Vaihinger. Schlick's principal conclusion was that
Logical Positivism never denies the reality of material objects but,
rather, equates physical reality with the lawfulness of
experience. Unfortunately, Planck, who had always supported
Schlick in the past, misunderstood the essay, interpreting it as a
polemic for Machian positivism, and harshly condemning it (Planck
1932).


## 8. The Protocol Sentence Controversy



The celebrated 'protocol sentence controversy' in the
Vienna Circle was initiated by Carnap's syntactic analysis of
observation sentences, or 'protocols' (Carnap 1932a). The
salient feature of Carnap's analysis was its
'syntacticism', the idea that meaning is wholly a function
of the serial arrangements of symbols. Naturally, syntacticism
precludes any effort to explain protocols by their relation to
'experiences', 'sensory impressions', or
'observations'. Otto Neurath criticized Carnap's
analysis, arguing that protocols should be understood
physicalistically, as sentences of the physical language, and their
origins and grounds are to be explicated naturalistically, by means of
behaviorist psychology (Uebel 2007, Ch. 8). But Schlick recoiled at
the very idea that the relation between observation sentences and what
they describe should be explicated by any means other than
philosophical analysis. So, in his classic 1934 essay, "On the
Foundations of Knowledge," he introduced so-called
'affirmations' (*Konstatierungen*) in the effort to
explicate the relation between physicalistic protocols and the
experiences on which they are grounded (Schlick 1979b, 370-387).
Otto Neurath responded, in his 1934 essay "Radical Physicalism
and the 'Real World'", condemning Schlick's
view as just so much metaphysics, while Carnap regarded affirmations
as protocols of a phenomenal language, along the lines of one of the
alternatives he had outlined in his 1932 paper, "On Protocol
Sentences" (Neurath 1983, 66; Carnap 1932b, 458-463). Still,
Carnap objected that, unless Schlick could explain how affirmations
might be translated into sentences of the physical language, then
affirmations violated the thesis of physicalism. Schlick responded
that affirmations, like "Here now white", were the
responses of investigators when asked about their personal experiences
in experimental situations. Thus construed, the demonstrative
character of affirmations ensures their incorrigibility (Schlick 2009,
661-674). Although their demonstrative character prevents them
from being regarded as proper physicalistic sentences, they are
obviously translatable into statements of the physical language. But
then, even though they lose their distinctive epistemic character, for
they are no longer incorrigible or indubitable, they still convey
epistemic warrant to their physicalistic translations. 




To Carnap, the deeper problem was that, by the lights of his 1934 work
on *The Logical Syntax of Language*, affirmations are not
well-formed expressions at all. Earlier, in his (1932a) contribution
to the protocol sentence controversy, Carnap's treatment of
observation was based on the Thesis of Metalogic, the idea that all
philosophical contentions (which are not nonsense) are metalinguistic
claims about linguistic expressions and their logical (particularly
syntactical) properties (Carnap 1932a, 435n). The function of the
Metalogic Thesis was to isolate pseudo-theses or statements which seem
to concern substantive matters but are really concerned with logical
or linguistic matters. Of course, these pseudo-theses became known as
'pseudo-object sentences' and their analysis became a
centerpiece of Carnap's *Logical Syntax*-era philosophy (Carnap
1937, Sec. 74). And the Metalogic Thesis, together with the Principle
of Tolerance (which asserts that the choice of any specific language
is a conventional decision), formed the principal theses of Carnap's
philosophy of logic in the Thirties (Carnap 1937, 51-2). Otto
Neurath, who endorsed the Metalogic Thesis and the Tolerance
Principle, drew the obvious conclusion that Schlick's defense of the
correspondence conception of truth, explicated by his analysis of
affirmations, committed him to the recognition of "the one, true
reality" and "the real world" (Neurath 1983,
pp. 106-8; Uebel 2007, Sec. 8.2). In short, Schlick's
foundations were spelled out in nothing more than philosophical
pseudo-statements.




What Neurath and (presumably) Carnap both missed was that
Schlick's thinking about meaning and linguistic significance had
come a long way since his 1926 essay on "Experience, Cognition,
and Metaphysics", in which he tried to link Wittgenstein's
remarks about internal relations in the *Tractatus* with his own
doctrine of implicit definition (Wittgenstein 1921, 4.122, 4.125,
4.1251, 5.232). There the goal was to apply both these ideas to the
distinction between intuitions and concepts. The result was
something of a disaster. For it implied what Schlick called
"The Incommunicability of Contents", the idea that any
effort to communicate non-formal contents, like the greenness of the
color green or the distinctive smell of wood smoke, must forever remain
ineffable (Oberdan 1996, Sec. 2). But it was not long before
Schlick's efforts to explain linguistic meaning and scientific
knowledge in terms of their 'form' and
'content' were abandoned and by the 1934-1935 academic
year, he was developing what might well be called 'a semantic
conception', spelled out in terms of grammars and the rules which
constitute them, and presenting his new vision of language in his
lectures on "*Logik und Erkenntnistheorie*"
(Schlick 1934-5).


## 9. Grammar and Meaning




In "*Logik und Erkenntnistheorie*," Schlick thought
the most important component of languages are grammatical rules, which
are of two kinds. First of all, there are 'internal
rules', which govern the use of expressions in relation to other
expressions, much like the formation and transformation rules of formal
logic. In addition, Schlick conceived of a second type of
grammatical rule, which he called 'application-rules'
(*Anwendungsregeln*), regulating the use of expressions in
connection with, or application to, observable extra-linguistic
situations. Of course, application-rules govern not only
descriptions of observable situations, but the use of indexicals and
demonstratives as well, thus legitimizing Schlick's affirmations
by grounding them in grammar. And Schlick conceived grammar with
sufficient breadth to encompass the natural languages of everyday life
as well as the technical and highly regimented languages of
science. Concurring with Carnap's Principle of Tolerance,
Schlick regarded the choice of grammatical rules, the choice of a
particular grammar rather than an alternative, as conventional and
therefore independent of extra-linguistic matters. And his
endorsement of grammatical conventionalism was specifically intended to
accommodate choices between languages which differed radically, as
demonstrated in his treatment of philosophical pseudo-problems
(Oberdan 1996, Sec. 3).




Schlick presented his latest conception of grammar as well as its
application to philosophical pseudo-problems in his 1936 essay on
"Meaning and Verification" (Schlick 1979b,
456-481). In particular, he demonstrated that the criterion of
verifiability is rooted in grammar and concerns any grammatically
well-formed proposition which is neither analytic nor
contradictory. He reiterated his conception of grammar as the
collection of rules governing the formation and use of meaningful
expressions, including the rules governing the use of language in
connection with experience, rules which are introduced by acts of
ostension (Schlick 1979b, 464-7). Although the result is an
analysis of language which provides a powerful treatment of many
'typical' metaphysical theses, like Platonism,
psychologism, and phenomenalism, in "Meaning and
Verification" Schlick demonstrated its utility by applying it to
solipsism. The upshot is that solipsism is a contingent truth which is
treated by its defenders as unfalsifiable. But statements which are
insulated from the possibility of falsification are object-language
'mis-expressions' of what are, at bottom, grammatical
rules. The parallel with Carnap's analysis of pseudo-object sentences
as metalinguistic assertions rather than 'real-object'
sentences could not be more striking. And just as Carnap regarded the
formal mode translations of philosophical theses as proposals to adopt
a certain language form, Schlick contended that the solipsist's thesis
was not a *bona fide* contingent claim but simply an attempt to
introduce a particular mode of speech. Thus, by the time of
"Meaning and Verification", he had moved well beyond his
'Form and Content' stage, modulating the virulent
Positivism of his earlier thinking, to arrive at a more mature and
balanced conception of the issues at the focus of his philosophical
concerns (Oberdan 1996, Sec. 5).


## 10. Death




As Schlick was leaving class on June 22, 1936, he was shot four times
in the legs and abdomen by Johann Nelbock, a former philosophy
student who had been threatening Schlick for several years. In fact,
Nelbock had been confined in an asylum for observation and
diagnosed as a paranoid schizophrenic. Eventually, other factors
-both social and political- emerged which may also have
influenced Nelbock. The number of possible motivations make it
nearly impossible to fully understand what was in Nelbock's mind
at the time of his murderous actions. But the result of his misdeed
is clear: with the death of Moritz Schlick, philosophy lost one of its
most creative thinkers. See Stadler 2001 (Part 2, Sec. 3-3.2) for a
comprehensive account of Schlick's death.