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sentation, insofar as we are affected by it.” This means that a sensation
is a state caused in the perceiver by the presence of an object. Kant
adds the quali¬cation “insofar as we are affected by it” because he
will argue (as foreshadowed at B1) that experience also provides the
occasion for the subject to contribute a priori representations. This
de¬nition implies, then, that sensation supplies the a posteriori data of
sensibility. Later in the Critique (e.g., A28“9, B44“5) Kant emphasizes
that as effects on perceivers, sensations are inherently subjective, by
contrast with the representations of space and time. Kant next de¬nes

2 In the J¨ sche Logic, Kant de¬nes an intuition as a singular representation. See Lectures on Logic,
a
589. On this issue, see Hintikka, “On Kant™s Notion of Intuition,” Parsons, “Kant™s Philosophy
of Arithmetic,” and Thompson, “Singular Terms and Intuitions in Kant™s Epistemology.”
The Transcendental Aesthetic
40
an empirical intuition as “That intuition which is related to the object
through sensation.” In other words, an empirical intuition is an intu-
itive representation based on sensation. By contrast, pure intuition
is supplied a priori through the sensibility, and is not contingent on
the actual objects being sensed. Finally, Kant de¬nes an appearance
as “The undetermined object of an empirical intuition” (A20/B34).
Since “undetermined” means not conceptualized, this implies that an
appearance is constituted by the data given to the subject through
the sensibility. Unfortunately each of these de¬nitions raises more
questions than it answers.
Let us return to the term “intuition,” which has two related mean-
ings. Sometimes “intuition” means a conscious representation of a
particular object. At other times it means only the pre-conscious data
given through the sensibility. Now as we saw above, the blindness the-
sis (intuitions without concepts are blind) entails that all conscious
representations have both sensible and intellectual elements. In intro-
ducing this idea in the Analytic, Kant says, “Intuition and concepts
therefore constitute the elements of all our cognition, so that neither
concepts without intuition corresponding to them in some way nor
intuition without concepts can yield a cognition” (A50/B74). And in
the following paragraph he says, “Without sensibility no object would
be given to us, and without understanding none would be thought”
(A51/B75). Thus the suggestion in the Aesthetic that humans can
consciously represent objects by intuition alone is misleading. What
Kant should say is that the sensibility supplies the intuitive data for
representing objects, but that this data, prior to all intellectual pro-
cessing, is not yet a representation of which we are conscious. So here
is the ¬rst quali¬cation: throughout the Critique “intuition” some-
times refers to the pre-conscious data received through sensibility, and
sometimes to a conscious, intellectually processed perception. Cor-
respondingly, the term “empirical intuition” sometimes refers to the
raw empirical data, and sometimes to a conscious perception of an
empirical object. In the Aesthetic, Kant wants to identify just those
elements provided by the sensibility, and particularly those supplied a
priori, apart from all intellectual processes. Hence where appropriate
I replace his references to intuitions of objects by references to the
data given in intuition.
The Transcendental Aesthetic 41
The main question raised by the term “sensation” is whether it
refers to a mental state or a state of the perceiver™s body. There are
texts supporting both readings. In some passages Kant appears, like
Descartes, to take sensations as mental states representing qualities,
such as colors, sounds, and hot and cold. On the traditional causal
theory of perception, to which Kant evidently adheres, experiences
of these qualities are caused by contact between a physical object and
the perceiver™s physical sense organs. The physiological processes this
contact triggers in the nervous system result in a state of conscious-
ness of some sensible quality. The question is whether Kant thinks
of sensations as the physical changes in the perceiver™s body or as the
resulting mental states. At B44 he refers to “the sensations of colors,
sounds, and warmth, which, however, since they are merely sensa-
tions and not intuitions, do not in themselves allow any object to be
cognized.” Here he appears to use “sensation” for the conscious expe-
rience. Other references to sensation could also be taken in this way.
But there are strong reasons to think sensations are states of the body.
Falkenstein makes a persuasive case for this reading, pointing out
that Kant describes sensations as “ordered and placed” in space and
time (A20/B34).3 If sensations are ordered spatially, then they must
have spatial location and characteristics, so they must be physical
states. Since Kant holds that secondary qualities as we perceive them
are not real physical properties of bodies, this is a good reason to think
sensations are physical states of the perceiver rather than the qualities
we consciously experience.4 In any case, since the causal theory postu-
lates a correspondence between the physical state of the perceiver and
the experienced quality, our decision here will not affect our reading
of Kant™s arguments in the Aesthetic.
Finally we need to return to Kant™s de¬nition of “appearance” as
whatever is given in sensible intuition. This could apply to conscious
representation of the object, or to the intuited object itself. Kant uses
it both ways in the Critique. The main use of “appearance” is in

3 See Falkenstein, Kant™s Intuitionism, chapter 3, 103“34, for a detailed argument for this inter-
pretation.
4 At A172/B214 Kant says, “every sense must have a determinate degree of receptivity for the
sensations.” Moreover, at A21/B35 he describes impenetrability, hardness, and color as “that
which belongs to sensation” rather than sensations themselves.
The Transcendental Aesthetic
42
contrast to “thing in itself,” which clearly is an extra-mental thing.
Because the ultimate thrust of the critical philosophy is to argue
that knowledge is only of appearances and not things in themselves,
it seems clear that appearances are fundamentally mental. At the
same time, Kant will argue that appearances in general are not illu-
sions, that they have objective features. So generally “appearance”
means the empirical object we experience through the sensible data of
intuition.
The last two sets of terms are less problematic. Kant™s distinction
between the matter and form of intuition is functional: the matter
consists in the (intuited) elements, the form in the system for ordering
and relating them. In the Aesthetic, Kant argues that space and time
are merely the forms, systems of relations, lying “in the mind a priori”
(A20/B34), in which we receive sensations, the data given through our
contact with objects. In the Analytic, Kant will argue that humans also
possess certain a priori forms of thought or conceptual schemes for
ordering and relating the appearances given in sensibility. In general, a
form of experience, whether supplied by the sensibility or the intellect,
is a system for ordering and relating some content, which functions
as the matter relative to that form.
Finally Kant distinguishes between inner and outer sense. As
described at A22“3/B37, outer sense is our means of intuiting external
objects, and inner sense is our means of intuiting our own mental
states. Now in the de¬nition, the phrase “objects as outside us” is
ambiguous. It could mean either spatially external to or numeri-
cally distinct from the knowing subject. I take the latter meaning as
primary: since inner sense is our means of intuiting our own mental
states, outer sense must be our means of intuiting anything distinct
from our own mental states. Moreover, if “outer” meant spatially
external, then Kant™s conclusion that space is the form of outer sense
would be tautological. As for inner sense, Kant says by its means “the
mind intuits itself, or its inner state,” although it does not produce an
intuition “of the soul itself, as an object.” The function of inner sense
is to provide a direct awareness of our own mental states, which is all
we can intuit of the self as knowing subject. Inner sense is a kind of
re¬‚ective awareness. Kant™s theory that space is the form of outer sense
and time is the form of inner sense means ¬rst, that everything that
we intuit as distinct from our own mental states must be located in
The Transcendental Aesthetic 43
space; second, all mental states occur in time. Kant adds that “Time
can no more be intuited externally than space can be intuited as
something in us” (A23/B37). His point is that all representations are
inherently temporal. Similarly, space is not “in us” as a formal feature
of representing, as time is.
In this discussion Kant treats outer and inner sense as parallel and
independent modes of awareness. This is misleading, however, since
there are important differences between them. For one thing, Kant
views time as more universal than space, since time is a condition for
representing things outside the mind as well as our own mental states.
Space, by contrast, is only the form of outer intuition (A34/B50).
Another essential difference surfaces later in the section called the
Refutation of Idealism, added in the B edition. Here, at B274“9, Kant
argues that inner sense presupposes outer sense. Most commentators
agree that Kant should have treated space and time together because
of their interrelations. To understand the theory of the Aesthetic,
however, we can consider outer and inner sense as parallel.
Before examining the arguments, let us review the de¬nitions dis-
cussed so far:

An intuition is the kind of representation in which the knower
immediately apprehends a “given” or existing state of affairs.
More precisely, through intuition we are given a manifold (mul-
tiplicity) of sensible data for representing whatever exists.
Sensibility is our human capacity to intuit objects. Human sensi-
bility has two modes: an outer sense consisting of our physical
sense organs for intuiting things distinct from the mind, and a
re¬‚ective inner sense for intuiting our own mental states. In both
forms sensibility is passive or receptive rather than active.
The empirical data of intuition are originally given through sensa-
tions, which are modi¬cations of the sense organs. These physical
states result in representations of sensible qualities such as color,
taste, and hot and cold. Both the sensations and their corre-
sponding qualities are subjective effects in perceivers, since they
depend on the perceiver and the conditions of perception as well
as on objects. These empirical elements constitute the matter of
experience: sensations are the matter of intuition; consciously
represented qualities are the matter of appearance.
The Transcendental Aesthetic
44
Finally, all intuitive representations of which we are conscious are
appearances. The appearance is whatever is given to us through
sensibility. Sometimes by “appearance” Kant just means the con-
sciously represented intuitive data, both empirical and pure, and
sometimes he means the object so represented.

2. the pure forms of int ui t ion a n d synth eti c
a p r i o r i kn ow led g e
At A21/B35 Kant says transcendental aesthetic is “a science of all
principles of a priori sensibility.” In this section he will argue that
human sensibility contains two pure forms of intuition, space and
time, which are the basis of the synthetic a priori cognitions expressed
in mathematics and physics. Because these forms are contributed by
the subject, Kant will argue that they can account for the necessity
and universality characteristic of these sciences.
Before presenting his arguments, Kant sketches three possible the-
ories of space and time. He ¬rst says space and time could be “actual
entities.” This refers to the absolute theory of space and time as pro-
pounded by Isaac Newton and followers such as Samuel Clarke, who
defended it in the Leibniz“Clarke Correspondence.5 The absolutists
thought of space and time as real (although non-material) contain-
ers of all spatial and temporal objects. Because these “containers” are
necessary conditions of the existence of spatiotemporal objects, they
exist independently of the things occupying them. In this sense space
and time are both real and objective. Moreover, they are prior to the
objects they contain in two senses: ¬rst, objects must exist in space
and time, although space and time could exist without them (God
could have created empty space and time); and second, the spatial and
temporal relations among objects are derived from the spatiotempo-
ral positions these objects occupy. Absolute space and time are also
real as opposed to ideal, since their existence does not depend on the
experience of perceivers. Even if perceivers never existed, and even if
material objects never existed, absolute space and time could exist.

5 The classical texts are Newton™s Mathematical Principles of Natural Philosophy, 1:6“10; and
Leibniz, The Leibniz“Clarke Correspondence. I discuss these theories in Space and Incongruence,
chapters 2 and 3.
The Transcendental Aesthetic 45
As a second possibility, space and time could be “only determi-
nations or relations of things, yet ones that would pertain to them
even if they were not intuited.” This refers to the major competitor
to the absolute theory, the relational theory of space and time. It was
championed by both rationalists and empiricists, including Leibniz
and Berkeley.6 In general, relationists believe that space and time are
merely systems of relations whose existence depends on the prior exis-
tence of both perceivers and the objects or elements so related. Despite
their epistemological differences, Leibniz and Berkeley both criticize
the absolute theory as incoherent, since it entertains the existence of
real entities that are not themselves substances. For relationists, spa-
tial and temporal relations among things are constructed from the
(non-spatiotemporal) properties and relations of metaphysical sub-
stances. Although Leibniz™s monadic substances are not themselves
spatiotemporal, our experience of space and time corresponds to their
real properties. This is why Kant says relational space and time would
belong to things “even if they were not intuited.” The relationists
held space and time to be ideal and subjective, since they are “con-
structed” through mental processes involved in representing existing
things. Here the priority relations are reversed: empty space and time
could not exist, since where there are no substances there could be
no system of relations derived from them. And although spatiotem-
poral relations correspond to properties of monadic substances, their
peculiar spatial and temporal character depends on the perceptual
process.
The ¬nal possibility is Kant™s own theory, that space and time are
pure forms of human intuition. This theory denies both that they
are absolute or real as things in themselves, and that they are derived
from a prior experience of non-spatiotemporal things. Although Kant
rejects both the absolute and relational theories, his position incorpo-
rates some features of each. He will agree with the Newtonians that
space and time are logically independent of the objects they contain,
but he will deny that they are completely independent of human per-
ceivers. Kant will accept Leibniz™s view that things in themselves are
6 In addition to the Leibniz“Clarke Correspondence, Leibniz™s position is spelled out in “First
Truths,” and the letter to Bayle of 1702, both in Philosophical Papers and Letters, 268“71 and
583. Berkeley™s views appear in De Motu in The Works of George Berkeley Bishop of Cloyne,
4:1“52; and A Treatise Concerning the Principles of Human Knowledge, part I, articles 110“17.
The Transcendental Aesthetic
46
not spatiotemporal, but he will reject the idea that space and time are
constructed from relations or properties of experienced substances.
We shall see how he argues for these views in the metaphysical expo-
sition of space and time.
Kant™s strategy in the Aesthetic is complex but methodical. First
he divides the arguments or “expositions” into two kinds. The meta-
physical exposition exhibits the concept “as given a priori” (A23/B38).
Here Kant presents four arguments to establish that space and time
are a priori forms of sensible intuition, without presupposing that
we have synthetic a priori knowledge. The transcendental exposition,
which was separated out in the B edition, begins with the premise that
we have synthetic a priori knowledge, and argues that space and time
must be pure forms of intuition to account for that knowledge.7 On
this reading, the two expositions draw the same conclusion, but differ
in their starting points. The advantage of this strategy is to appeal to
readers whatever their position on synthetic a priori knowledge.
Following his treatment of outer and inner sense, Kant separates
the expositions of space and time. Although he intends the arguments
to be parallel, his presentation is sloppy and the arguments are not
properly arranged. First, whereas there are four arguments in the
metaphysical exposition for space, there are ¬ve for time. This is
because Kant mislocates the transcendental exposition in the third
paragraph of the metaphysical exposition. In addition, although Kant
is defending the same conclusions for space and time, we shall see
that the proofs occasionally differ. For the most part, however, the
thrust of the arguments is the same, so we shall generally treat them
together.
The ¬nal preliminary remark concerns the fact that Kant subtitles
these sections expositions of the concepts of space and time. Since he
is arguing that space and time are pure forms of intuition, and since
intuitions and concepts are distinct kinds of representations, this
heading is cause for confusion. The explanation, however, involves
Kant™s blindness thesis, according to which we are not conscious of
the intuitive data prior to any intellectual processing. Thus Kant

7 In “Kant™s ˜Argument from Geometry™,” Lisa Shabel argues, by contrast, that the transcen-
dental exposition assumes the conclusion of the metaphysical exposition, and then shows
how this analysis explains the synthetic a priori nature of geometry.
The Transcendental Aesthetic 47
cannot begin with premises describing this data. Instead, he must
analyze our conscious experiences of space and time, and then argue
that these experiences could have the features they do if and only if
space and time are forms of intuition. So the most straightforward
solution is to take the term “concept” here to refer to a representation
that has been intellectually processed, which includes perceptions
of spatiotemporal objects. In the expositions, as we shall see, Kant
returns to the standard use of “concept” for a general representation,
as opposed to an intuition.


A. The metaphysical exposition
The metaphysical exposition argues that our original representations
of space and time are a priori intuitions. The ¬rst two proofs conclude
that these representations are known a priori, supplying necessary
features of experience. The last two conclude that they originate in
intuition as part of the manifold given in sensibility. Putting these two
conclusions together yields the result that our original representations
of space and time are a priori or pure forms of sensible intuition.

1. The ¬rst exposition: space and time are logically independent
of the empirical data given in intuition
Here Kant argues that space and time are a priori in the weak sense
that they are not derived from the empirical data given in experi-
ence. The premises refer to this empirical data as sensations, and,
as we saw earlier, sensations are physical states of the perceiver. But
because the sensible qualities we consciously represent correspond to
these physical states, I shall refer to both sensations and sense qual-
ities as the empirical data given in intuition. The main point here
is that cognitions of space and time are not constructed from the
empirical data, and hence are not known a posteriori. As Falkenstein
explains, this argument is aimed against philosophers who held sensa-
tionist, constructivist theories of space and time cognition. This group
would include relationists such as Leibniz and Berkeley, as well as
Locke for his theory of time. Kant believes the empirical sensible
data are received in spatiotemporal arrays. Here is the argument for
space:
The Transcendental Aesthetic
48
For in order for certain sensations to be related to something outside me (i.e.,
to something in another place in space from that in which I ¬nd myself ),
thus in order for me to represent them as outside one another, thus not
merely as different but as in different places, the representation of space
must already be their ground. (A23/B38)

This is the argument for time:
For simultaneity or succession would not themselves come into perception
if the representation of time did not ground them a priori. Only under its
presupposition can one represent that several things exist at one and the
same time (simultaneously) or in different times (successively). (A30/B46)

The point is that any constructivist theory of space and time would
actually have to presuppose spatial and temporal systems of relations.
Now why does Kant think this?
One interpretation takes Kant™s premises to be based on
introspection: it just is apparent that the sensible data, whether pre-
conscious sensations or qualities experienced consciously, are given in
space and time. The color patches we see, for example, are spatially
extended and related to each other. Correspondingly, the physical sen-
sations causing these representations are located in our sense organs,
and are brought about by contact with objects located in space. The
same can be said for their temporal locations and relations. So it is
an obvious fact that the intuitive data are given in space and time.
While this version is plausible, it may not completely capture Kant™s
point. First, it does not explain why Kant thinks any constructivist
account must presuppose space and time. One might object that for
all we know, the pre-conscious data may not be ordered in space and
time. In this case the spatial and temporal frameworks we consciously
experience might arise through some constructive processes, as rela-
tionists maintain. To eliminate this possibility a stronger argument is
needed, that a constructivist account is not a possible account of our
experience.
Kant™s premises suggest such an argument, in effect a dilemma for
the constructivist, who thinks space and time are created from the
relations of the sensible data given empirically. Now either these rela-
tions are themselves spatiotemporal or they are not. If they are spatio-
temporal, then they presuppose the spatial-temporal frameworks
The Transcendental Aesthetic 49
encompassing such positions. So the constructivist cannot embrace
the ¬rst horn of the dilemma without begging the question. On the
other hand, if the relations among the sensible data are not spatial
and temporal, then the constructivist must explain how spatial and
temporal positions arise from these non-spatiotemporal features. This
horn of the dilemma has two aspects to it, one general and one spe-
ci¬c. The general problem is the one just stated, how one derives any
spatiotemporal features out of non-spatiotemporal features. The spe-
ci¬c problem is one Falkenstein calls the “localization” problem: if the
sensible elements are not given in spatial and temporal arrays, then
what could possibly determine the particular order or con¬gurations
in which they are experienced? Any answer to this question could
only be pure speculation. More important, it is hard to see how the
qualitative features of color patches could determine anything about
the order in which they are experienced. The spatiotemporal positions
and relations of the sensible data appear completely independent of
the content of that data.
The problem for the second horn relates to another point implicit
in the argument. Consider that for any theory that maintains that
global space and time are constructed from relations among sensible
elements, the elements must ¬rst be discriminated as numerically dis-
tinct. This requires identifying the individual relata independently of
their spatiotemporal positions. Now the exposition for space implies
that spatiotemporal position is both necessary and suf¬cient for dis-
criminating distinct sensible elements. Kant says we represent the
sensations “as outside and next to one another, thus not merely as dif-
ferent but as in different places” (A23/B39). Consider, for example,
how we identify two qualitatively identical color patches as numeri-
cally distinct. It can only be because of their different spatiotemporal
locations.
The ¬rst exposition argues that the original spatiotemporal mani-
folds are independent of the empirical data given in them, although
they are given with that data. In other words, the sensible manifold has
two aspects: the empirical data given a posteriori, and the spatiotem-
poral systems in which they are located. The logical independence of
these systems establishes their a priori status in the weak sense that
their content is not derived from the empirical data.
The Transcendental Aesthetic
50
2. The second exposition: space and time are necessary conditions
of experience
Here Kant argues that space and time are a priori in the strong sense

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