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Critique of Pure Reason

Lecture Notes: Transcendental Deduction

G. J. Mattey

Chapter II of the Analytic of Concepts, “On the Deduction of the Pure Concept of the Understanding,” is one of the most daunting texts in all of philosophy. It lies at the very heart of Kant’s project, as he had communicated it to Herz in 1772: to show how pure concepts of the understanding can refer to objects that are given in experience. Kant recognized its centrality and also the difficulty of following the argument, for “in fact the matter itself is deeply shrouded” (A88/B121).

The Deduction is one of the chapters that was completely re-written for the second edition. The style and substance of the two versions are quite different. The “A Deduction” of the first edition is much looser in its presentation and focuses on a number of mental processes that are downplayed in the “B Deduction” of the second edition. We will here examine only the B Deduction.


Kant used an analogy from law to describe the task that lay before him. In the courts, a distinction is made between questions of fact (did he actually do what he is accused of doing?) and questions of right (was it legally permitted for him to do so?). To decide questions of fact, the courts appeal to testimony and material evidence, both of which are appeals to experience. To decide questions of right, however, the courts appeal to rules of law. Establishing, on the basis of rules, whether an action is right is called, by Kant, a “deduction.”

On trial, so to speak, are the pure concepts of the understanding, whose existence Kant had tried to establish in the metaphysical deduction. There is no question of fact about whether we do use these concepts. For example, even non-philosophers casually attribute causal efficacy to objects. But there is a vital question of right. It is the question Kant posed to Herz. As Kant noted in the Prolegomena, Hume had established that experience cannot give us the right to use a pure concept of cause or substance (Preface, Ak 4:257ff). “Yet we do need to know how these concepts can refer to objects even though they do not take these objects from any experience” (A85/B117). That is, we need a deduction of the pure concepts of the understanding.

We can establish the right to apply empirical concepts to objects by appealing to the fact that the concepts originated from those very objects. When we form an empirical concept by comparing our perceptions of individual objects, we “ascend from singular perceptions to universal concepts” (A86/B119). Such an account of the origin of empirical concepts could be called an “empirical deduction.” No empirical deduction could establish our right to apply pure concepts to objects, since those concepts are supplied by the pure understanding, and not the objects themselves. So we need a “transcendental deduction” of the categories. To treat a cognition transcendentally is to investigate the possibility of its having an a priori origin yet applying to objects.

Kant informs us that there has already been a transcendental deduction of the concepts of space and time in the Aesthetic (A87/B119-20). We can say that objects are in space and time because space and time are the forms of sensible intuition of objects. That is, we cannot intuit an object without assigning it a position in time, and if the object is outer, in space as well. “For only by means of such pure forms of sensibility can an object appear to us, i.e., can it be an object of empirical intuition” (A89/B121).

The pure concepts of the understanding, on the other hand, are not conditions for something to be an object of empirical intuition. “Therefore objects can indeed appear to us without having to refer necessarily to functions of the understanding, and hence without the understanding’s containing a priori the conditions of these objects” (A90/B122). This possibility is illustrated by Hume’s case of the concept of a cause. According to this concept, when A (the cause) occurs, B (the effect) must occur as a result. Experience may allow us to generate by induction an empirical rule “whereby something usually happens” (A91/B124), but it cannot give us a rule according to which things must happen in a certain sequence. So, “appearances might possibly be of such a character that the understanding would not find them to conform at all to the conditions of its unity” (A90/B123).

The Possibility of Experience

We saw that in the Preface to the second edition, Kant proposed a “Copernican revolution” in philosophy. Rather than pursuing the hopeless task of showing how pure concepts must conform to objects, we can hope for success if we assume that objects must conform to our concepts (Bxvii). This is a reference to §14, “Transition to the Transcendental Deduction of the Categories.” Here Kant notes that since objects of intuition must conform to a priori forms of intuition, we can ask “whether concepts do not also a priori precede [objects], as conditions under which alone something can be, if not intuited, yet thought as object as such” (A93/B125).

But why would pure concepts be required for us to think something given in intuition as an object? The answer is that the concept would be required for the intuition to reach the status of experience, as opposed to mere appearance. “All experience, besides containing the senses’ intuition through which something is given, does also contain a concept of an object that is given in intuition, or that appears” (A93/B126). This is a crucial claim on Kant’s part, yet he says nothing at this point as to why this is so. We ordinarily use the term ‘experience’ somewhat loosely and frequently without reference to concepts. But this loose sense of ‘experience’ is what Kant would call instead “appearance.”

If a priori concepts must be applied to intuitions in order for them to rise to the level of experience, we have a foundation of a deduction of their applicability to objects. “All empirical cognition of objects necessarily conforms to such concepts, because nothing is possible as object of experience unless these concepts are presupposed” (A93/B126). The reference of the categories to objects, their “objective validity,” then would be based on the fact that they make experience possible.

In the second edition, Kant diagnosed the central difficulty of empiricism, which traces the origins of all concepts to experience. Locke had tried to derive what Kant took to be pure concepts from experience and then he tried to apply them to objects beyond the scope of experience, and so “left the door wide open for fanaticism” (B128). Hume recognized that concepts which would apply to objects beyond experience must originate in the understanding. But he could not see how such concepts would apply to experience, which only yields concepts based on custom and habit. At least he was consistent in that he did not try to apply those empirical concepts (such as that of cause) to objects beyond experience, and so he “surrendered entirely to skepticism” (B128). (Kant probably had Hume’s Dialogues Concerning Natural Religion in mind here. See Prolegomena, Conclusion, §67, Ak 4:356.)

An Example

The last preparatory step before the deduction proper is an explication of what categories are: “they are concepts of an object as such whereby the object’s intuition is regarded as determined in terms of one of the logical functions in judging” (B128). Recall that a function is the unity of presentations. In the case Kant describes, a categorical judgment that S is P, the unity is the result of placing the “sphere” (what we now call the “extension”) of the subject S within the sphere of the predicate P.

Now suppose we have an empirical intuition, which we can bring under the empirical concepts body and divisible. Two different true categorical judgments can be made using these concepts: All bodies are divisible, and Something divisible is a body. In the first, body is the subject and divisible is the predicate, and vice-versa in the second. Kant seems to have thought that one of the two is more properly the subject; one of them is the concept “we want to give the function of the subject” (B129). But logic alone cannot determine which one it should be.

If the concept body is brought under the pure concept substance, we know that body properly applies to the subject position, insofar as a substance is understood as that which is not the predicate of any subject. So any intuition that falls under the concept body is “must be considered always as subject only, never as mere predicate” (B129). In this way the intuition is “determined” in terms of the logical form of subject by being thought through the concept body, which in turn is thought as substance.

It should be noted that modern logic does not distinguish between subject and predicate as did Aristotelian logic. In effect, both “body” and “divisible” are predicates, and the subject (so to speak) would be what Kant calls the intuition. The universal categorical judgment All bodies are divisible would be understood as: For any x, if x is a body, then x is divisible. The judgment Something divisible is a body would be rendered as For some x, x is a body and x is divisible. The intuition would be the value of the variable ‘x,’ and both of the predicates may apply to it.

Synthetic Unity

Kant’s key premise in the transcendental deduction is given at the start of §15. Through sensibility, only a manifold can be given. If that manifold is to be combined by an act of “synthesis” into the presentation of an object, the spontaneity of the understanding must be that which does the combining or synthesizing. The argument for this claim seems to rest on an ambiguity, though. We must grant that combining, because it is an activity, cannot be the work of sensibility, given that it is merely receptive and not spontaneous. But we might ask why sensibility does not present us with objects which are already “combined” or perhaps “bundled,” in the sense of being presented as unities of manifolds. But combination is a presentation, we are told, which cannot be found in an object as given to us.

A further point is that analysis, or resolution into components, presupposes combination. The slogan in the Kant literature for this claim is, “no analysis without prior synthesis.” (But again, Kant supposes that the synthesis is carried out by the mind, so that nothing comes to the mind as already synthesized.) The outcome of synthesis is the unity of the manifold. Conceptually, unity is more fundamental than synthesis, since it is a component of the concept of a unified manifold, which is what synthesis brings about. The unity presupposed by synthesis is not the category of unity, because the concept of a category presupposes that of unity as well. Having argued for the need for unity in synthesis, Kant sets about to find its source. His target is “what in itself contains the basis for the unity of different concepts in judgments, and hence contains the basis for the possibility of understanding, even as used logically” (B131).


In §16, Kant finds the source of synthetic unity, though not where one might expect to find it. He begins the section by introducing a kind of persentation which he calls “the I think” (das: Ich denke). The “I think” is a presentation of one’s self as thinking a given presentation. (For example, I am thinking that a triangle has three sides.) Kant claims that it must at least be capable of accompanying any presentation. So the claim is that I must be able to present myself as thinking any of my presentations. Kant calls self-presentation in general “apperception.” The term was originally coined by Leibniz. (See New Essays Concerning Human Understanding, where “apperceptions” are perceptions of perceptions, whose absence explains unperceived “little perceptions” and innate ideas.)

The kind of self-presentation under discussion is pure, not empirical. I know a priori that I can present my presentations as mine. This is different from knowing from experience what my mental states are at one time or another (which is the product of inner sense, see A33/B49-50). So the self-presentation that must be capable of being attached to all my presentations is called “transcendental apperception.” It is also called “original apperception,” “for it is the self-consciousness which, because it produces the presentation I think that must be capable of accompanying all other presentations and is one and the same in all consciousness, cannot be accompanied by any further presentation” (B132). A further reason for calling this kind of apperception original is that it alone among all presentations is capable of accompanying all others.

Since there is only one “I think” that must accompany all my presentations, apperception is unified. So Kant will speak of the “transcendental unity of apperception.” This is not a kind of object, but rather a feature of transcendental apperception. It might be called more straightforwardly “the unity of transcendental apperception.” Kant then describes this unity as “original combination” and says that from it “much can be inferred” (B133). The combination seems to be “the condition under which alone [my presentations] can stand together in one self-consciousness.”

We must be very careful here. Kant has already used the word ‘combination’ in the sense of an activity of combining. This may lead us to think that “original combination” is some primordial act of combining. But nothing to this point justifies that claim, since the only basis for postulating “original apperception” is that I can refer all my presentations to myself. We have no reason, at least yet, to think that my presentations are all referred to myself, even if they all belong to myself. The fact that they are all mine does not seem to require actual self-consciousness, but only potential self-consciousness.

Having spoken generically of presentations being capable of being presented as my own, Kant moves to the specific case of intuition. He had already stated that sensibility provides the mind only with a manifold, and that it is the activity of the understanding which combines or synthesizes this manifold into a unity. It is this unity which elevates the manifold to the level of a cognition, or presentation of an object.

In order for me to combine the manifold into a synthetic unity, there must be a single “I” which does the combining. This is what Kant calls the “synthetic unity of apperception.” A better expression might be “unity of synthesis in one consciousness.” Kant claimed that this unity is a necessary condition for the “analytic unity of apperception.” This is the unity introduced previously: the presentation of the self as that to which all my presentations are presented. Kant thought that the unity of synthesis in one consciousness is fundamental. He says that “the principle of this unity [is] the supreme principle in all of human cognition” (B135). Further,

The synthetic unity of apperception is the highest point, to which we must attach all use of the understanding , even the whole of logic, and in accordance with it transcendental philosophy; indeed, this power is the understanding itself. (B134)
Again, we must be careful. The “power” referred to here must be the power to “combine a manifold of given presentations in one consciousness” (B133). It is not at all clear what this power has to do with self-consciousness. It could well be a process operating in the background, of which I am not aware at all.

At the end of §16, Kant finally draws an important conclusion from these considerations. The premise is that the synthesis of a manifold of intuition is a necessary condition for the presentation of myself as identical. The synthesis is required because the presentation of the “I” by itself is simple. For the “I” to have any content, something must be given to it, and for humans, this means that something must be given in intuition.

I am, then, conscious of the self as identical, as regards the manifold of the presentations given to me in an intuition, because I call them one and all my presentations that make up one presentation. (B135)
This by itself is a pretty modest claim. But Kant takes it further:
That, however, is tantamount to saying that I am conscious a priori of a necessary synthesis of them. This synthesis is called the original synthetic unity of apperception. All presentations given to me are subject to this unity; but they must also be brought under it through a synthesis. (B135-6, with a variant reading from Pluhar’s footnote 208)

Now we must be extremely careful. All Kant is able to claim so far is that if I am to become conscious of a number of presentations as belonging to a single “I,” they must be combined in a single consciousness. This is the only sense in which there is a “necessary synthesis.” A certain kind of synthesis, synthesis in a single consciousness, is a necessary condition for one to present one‘s consciousness as being unitary. In §17 he seems to recognize this point, by noting that the “proposition that makes the synthetic unity [of consciousness] a condition of all thought” is analytic.

For it says no more than that all my presentations in some given intuition must be subject to the condition under which alone I can ascribe them—as my presentations—to the identical self, and hence under which alone I can collate them, as combined synthetically in one apperception, through the universal expression I think. (B138)

Kant concludes §17 by contrasting the human understanding, which requires an act of synthesis to establish its unity, with another possible kind of understanding. This would be an understanding in which a manifold of intuition, and indeed the objects of that intuition, are given in its self-consciousness rather than being required for its self-consciousness. This would be an intuitive understanding, in contrast to the discursive understanding of humans, which only applies concepts to intuitions that are generated by sensibility. Kant says that we can frame no concept of such an understanding, or of an understanding whose material is intuitions not in space and time.

Pure Synthesis

In §18, Kant claims that, “Only the original unity of apperception is valid objectively” (B140). This means that the unity of apperception is a necessary condition for the presentation of an object. Here, for the first time, concepts are mentioned. We have been told that there is an end-product of the synthesis of the manifold presented in intuition. Now we are told that the manifold is “united in a concept of the object” (B139). The synthesis is required in order for one to present what is given in intuition as falling under a concept, that is, as being of one kind or another.

I might say, on the basis of sense-perception, “That is an apple.” This particular unification of a manifold under a concept is empirical, insofar as involves sensation and an empirical concept. Kant claims that such an empirical synthesis has as its basis, a priori, “the understanding’s pure synthesis” (B140). So what is this pure synthesis, and why should we think there is such a thing?

The answer takes us a step further in the deduction. A pure synthesis might be the combination of elements that are “pure.” Kant seems to indicate this by referring to “the pure form of intuition in time” (B140). This intuition contains a manifold, and insofar as it does, it must be capable of being thought in a single consciousness. Here is how Kant describes this condition: “It is subject to that [original] unity [of consciousness] solely through the necessary reference of the manifold of intuition to the one [self], i.e., to the ‘I think’” (B140). This can take place, we have seen, only insofar as the manifold is combined. So it seems that the “pure synthesis” is some kind of synthesis of the manifold of time itself. The idea seems to be that the synthesis of the presentations given in intuition requires a synthesis of individual times into a single stretch of time. (But one must keep in mind the account of time in the Aesthetic, according to which time is an intuition because it is “the kind of presentation that can be given only through a single object,” so that times are parts of a single time (A32/B47).)

The Unity of Judgment

Thus far, the discussion of the unity induced by synthesis has been restricted to what is required for the presentation of objects. In §19, Kant extends the discussion to the synthesis that unites cognitions in judgments. In a judgment, we relate cognitions to one another, and this relation is one of combination or synthesis in one consciousness. So, “a judgment is nothing but a way of bringing given cognitions to the objective unity of apperception” (B142). It is objective, because judgments are meant to say something about the way things are, and not simply to report one’s subjective psychological states.

There is a “necessary unity” in judgments, even if they are empirical. This is not to say that such judgments are necessarily true, but only that “they belong to one another by virtue of the necessary unity of apperception in the synthesis of intuitions” (B142). Once again, all Kant has really established is that the unity of apperception is a necessary condition for the unification of cognitions in a judgment. But Kant seems to say more: “i.e., they belong to one another according to the principles of the objective determination of all presentations insofar as these presentations can become cognition—all of these principles being derived from the principle of the necessary unity of apperception” (B142).

We have already been told about the principle of the necessary unity of apperception. Now we are informed that this principle is the basis of other principles, which “determine” presentations so that they can become cognitions. To be a cognition is to present an object, so these principles would be required for our presentations to be more than merely subjective. So an objectively valid judgment, in which presentations “are combined in the object, i.e., combined independently of what the subject’s state is” (B142), would be subject to principles which are derived from the principle of the necessary unity of apperception. But Kant has said nothing yet about what these principles are or why there must be such principles.

The “Manifold” Argument

In §20, Kant finally pulls together the several threads that he had been developing in the first seven sections. Specific mention is made of §17 and §19. The conclusion of the argument is that “the manifold in a given intuition is subject necessarily to the categories” (B143). This seems to mean that this “manifold” can be brought under the categories. The key premise is that “the manifold given [which is found] in a sensible intuition is subject necessarily to the original synthetic unity of apperception” (B143). The premise is justified by reference to §17. What ties the apperception to the categories is judgment. The link between apperception and judgment is made in §19, and the link between judgment and the categories is made in the metaphysical deduction, in §10.

The following is a somewhat interpretive reconstruction of the argument of §20, drawing on some material from §21, which is a “Comment” on §20. This formulation of the argument is meant to make sense of the need for a second argument in §26.

  1. If the given manifold in an intuition presented as one (unified) empirical intuition, then necessarily that intuition is presented as belonging to a unified consciousness. [§17]
  2. So, if the given manifold of intuition is presented as one (unified) empirical intuition by an act of the understanding, then necessarily, that intuition is presented by that act as belonging to a unified consciousness. [1]
  3. If necessarily, an intuition is presented by an act of the understanding as belonging to a unified consciousness, then the intuition is determined by at least one logical function of judgment. [§ 19]
  4. So, if the given manifold of intuition is presented as one (unified) empirical intuition by an act of the understanding, then the intuition is determined by at least one logical function of judgment. [2, 3]
  5. The categories are the logical functions of judgment by which the manifold in a given intuition is determined. [§10]
  6. So, if the given manifold of intuition is presented as one (unified) empirical intuition by an act of the understanding, then the intuition is presented as determined by at least one of the categories. [4, 5]
  7. If an intuition is presented as determined by at least one of the categories, then it is subject to the categories.
  8. So, if the given manifold of intuition is presented as one (unified) empirical intuition by an act of the understanding, then it is subject to the categories. [6, 7]

The point of the argument on this reconstruction is that if we are to think an intuition as a unity by an act of the understanding, we must bring it under one consciousness (attach “I think” to the components of its manifold), and we do so by bringing it under categories. It remains to be seen, however, why the way an object is given in intuition as a unity is the way in which it is thought by the understanding as a unity.

So it will be shown in §26, “from the way in which the empirical intuition is given in sensibility, that the intuition’s unity is none other than the unity that (by §20, above) the category prescribes to the manifold of a given intuition as such” (B145). Compare this passage from §25: “Now cognition of ourselves requires not only the act of thought that brings the manifold of every possible intuition to the unity of apperception, but requires in addition a definite kind of intuition whereby this manifold is given” (B157). We find in §24 that the synthesis that is required merely for the unity of apperception “was not just transcendental but also purely intellectual only” (B150). This is in line with the way the conclusion of the argument has been presented here: that categories apply to a manifold insofar as they are presented by an act of the understanding (an intellectual act) as one (unified) empirical intuition.

Step 1 is given further support in Kant’s footnote in §21. The reason unified consciousness is needed for the presentation of a unified intuition is that a process of unification is required. “That unity always implies a synthesis of the manifold given for an intuition, and already contains the latter’s reference to the unity of apperception” (B145). It has already been noted that this claim is subject to dispute, which calls the truth of Step 1 into question. Steps 3 and 5 do not seem obviously true, but Kant did not see fit to try to support them beyond referring to earlier discussions.

Transcendental Synthesis

The argument for the second part of the transcendental deduction does not really get going until §24. In the intervening sections, Kant reiterates his account of the human cognitive apparatus. Object are given to us in intuition, and the pure concepts of the understanding have reference to objects only through intuition. The categories are therefore limited in their application. Although they apply to objects of intuition “as such,” as was shown in §20, if we try to apply them to objects other than those of our sensible intuition, “they are then empty concepts of objects, i.e., concepts through which we cannot judge at all whether or not these objects are so much as possible” (B148). Without objects given in intuition to which they could be applied, they are “mere forms of thought, without objective reality” (B148).

So how is it that the categories become more than mere thought-forms, but instead are concepts with objective reference or “validity?” The answer lies in the way in which objects are given to human sensibility—through the form of time. Kant had claimed in the Aesthetic that time is the form of all intuition, outer and inner (A54/B60). Here he tells us that time presents a pure manifold to the human mind, and that it stands in need of its own synthesis. The synthesis of the pure manifold is what Kant calls the “figurative synthesis,” as opposed to the intellectual synthesis described in §20.

When the figurative synthesis “concerns merely the original synthetic unity of apperception,” it is called transcendental synthesis (B151). The idea here is that if we unify times into one time, we necessarily bring it into a single consciousness. The figurative synthesis is the product of the imagination, which, though spontaneous, itself “belongs to sensibility” (B151). Kant sometimes refers to the imagination in its role of carrying out the figurative synthesis as the “productive imagination,” as opposed to the “reproductive imagination,” which is not spontaneous and follows empirical laws of association—the laws to which Hume had called attention (B152). The reproductive imagination plays no role in the transcendental deduction.

So now we have two syntheses in play. The first is the intellectual synthesis, which involves pure concepts whose application to objects is in question. The second is the figurative synthesis, which involves pure intuitions whose relation to pure concepts is in question. This latter synthesis determines the manifold of pure intuition, just as judgments determine given intuitions by thinking them under concepts. What the two have in common is that both bring their respective cognitions to unity in a single self-consciousness.

If the figurative synthesis succeeds in uniting a manifold of pure intuition under one self-consciouness, then it is automatically subject to the categories, and it gets a new name: “However, when the figurative synthesis concerns merely the original synthetic unity of apperception, i.e., merely this transcendental unity of thought in the categories, then it must be called the transcendental synthesis of imagination, to distinguish it from the merely intellectual combination” (B151). This is the vital link between concept and intuition. The two are brought together by the unity of consciousness on the side of concept and the synthesis of the pure manifold by the imagination on the side of intuition. “This synthesis is an action of the understanding upon sensibility, and is the understanding’s first application (and at the same time the basis of all its other applications) to objects of the intuition that is possible for us” (B152).

Kant presents an application of this link between intuitions and pure concepts by noting that even our inner intuition of ourselves requires a transcendental synthesis. Through inner sense we perceive a succession in time of presentations of our inner state. But this succession is not itself an intuition; rather it “contains the mere form of intuition but without combination of the manifold in this form, and hence contains as yet no determinate intuition at all” (B154). To say that successive intuition is determinate is to say that the intuition has a certain duration and position in time. This requires two things. First, it requires conceptualization of the succession as, say as being one minute long, and being at dawn. Second, it requires that the manifold of intuition be given the unity of an object by the activity of the imagination, since the presentations stretching over a minute come one-by-one.

Conceptualization requires judgment, and judgment requires synthesis in one consciousness. Concrete determination in an intuition requires the figurative synthesis, which also takes place in one consciousness. So, Kant maintains, the act of figurative synthesis is influenced by the understanding and its pure concepts. “Determinate intuition is possible only through the consciousness of the manifold’s determination by the transcendental act of imagination (i.e., by the synthetic influence of understanding on inner sense)—the act that I have called figurative synthesis” (B154).

Here Kant calls attention to a fact about human cognition that is really the model for his whole account of the relation between pure concepts and pure intuitions.

We cannot think a line without drawing it in thought. We cannot think a circle without describing it. We cannot at all present the three dimensions of space without placing three lines perpendicularly to one another at the same point. And even time we cannot present except inasmuch as, in drawing a straight line (meant to be the externally figurative presentation of time), we attend merely to the act of the manifold’s synthesis whereby we successively determine inner sense, and thereby attend to the succession of this determination of inner sense. (B154).
These acts of drawing, describing and placing all take place under the guidance of the understanding. “Hence by no means does the understanding already find in inner sense such a combination of the manifold; rather, the understanding produces it, inasmuch as the understanding affects the sense” (B155).


Before putting his results in the form of an argument in §26, Kant dealt at some length with a side-issue. The self is the object of inner sense. Previous philosophers have treated inner sense as revealing the activities of the self. A classic example is Locke, who defined “ideas of reflection” as being about the operations of the human mind (An Essay Concerning Human Understanding, Book II, Chapter 1). But for Kant, the activities of the self are to be found in the spontaneous operations of judgment and imagination. Inner sense, however, reveals only a succession of self-perceptions which themselves are passive.

The missing factor in the presentation of the self is that inner intuition can reveal the self only insofar as the object (the self) it presents is synthesized. So the self synthesizes the presentation of itself in inner sense. Or, as Kant put it, “we are inwardly affected by ourselves” (B155). This means that the self as presented to itself in inner sense is only appearance. “Hence although my own existence is not appearance (still less mere illusion), determination of my existence can occur only in conformity with the form of inner sense [time] and the peculiar way in which the manifold that I combine is given in inner intuition” (B158).

And since concepts need intuitions to be applicable to something, I can only cognize myself through the way that I appear in inner intuition, which itself is the product of my activity. Although we must present ourselves under the concept of thinking as an “intelligence,” we must still determine what we are thinking to present ourselves as object. So, “I cannot determine my existence as that of a self-active being; instead I present only the spontaneity of my thought, i.e., of the [act of] determination, and my existence remains determinable always only sensibly, i.e., as the existence of an appearance”(B158). The self can be determined only in time-relations, which must be given in intuition.

The “Synthesis” Argument

The first part of the deduction was intended to show that thinking objects “as such” through intuition “as such” is subject to the categories. The second part is to show that the cognition of objects of human sensible intuition is also subject to the categories. This would mean that these objects are subject to the “laws of combination” prescribed by the categories and “hence, as it were, to prescribe laws to nature, and even to make objects of nature possible” (B159).

Before presenting the argument, Kant introduces for the first time the expression “synthesis of apprehension.” This means “that combination of the manifold in an empirical intuition whereby perception, i.e., empirical consciousness of the intuition (as appearance), becomes possible” (B160). Kant gives two examples of such a synthesis. The first is the perception of a house, and the second is the perception of the freezing of water. The gist of the argument is that the synthesis of apprehension is subject to the categories, and so the categories apply to the objects of empirical intuition which are perceived through that synthesis.

(Note: the following reconstruction concerns the application of the categories to outer objects in space and time. For the single inner object, the “empirical self” or the self as it appears to itself in inner intuition, the argument can be adapted by eliminating the reference to space.)

  1. If an outer object is perceived, then its perception is the result of the synthesis of apprehension
  2. If the perception of an outer object is the result of the synthesis of apprehension, then the object is presented in a determinate location in time and space.
  3. If an outer object is presented in a determinate location in time and space, then it is presented relative to a priori forms of intuition. [Transcendental Aesthetic]
  4. If an object is presented relative to a priori forms of intuition, then it is presented subject to the rules which govern the synthesis of those forms.
  5. The rules which govern the synthesis of space and time are rules which refer the synthetic unity of space and time to the unity of self-consciousness.
  6. So, if an outer object is presented relative to a priori forms of intuition, then it is presented subject to the rules which refer the synthetic unity of space and time to the unity of self-consciousness. [1, 2, 3, 4, 5]
  7. The rules which refer any synthetic unity to the unity of self-consciousness are based on the categories.
  8. So, if an outer object is presented relative to a priori forms of intuition, then it is presented subject to the rules which are based on the categories. [6, 7]

The cogency of this argument depends on the acceptance of a number of claims Kant makes about the mechanisms of human cognition. We must accept that there is a synthesis of apprehension, that a house is not simply perceived, but that in its perception “I draw, as it were, the house’s shape in conformity with this synthetic unity of the manifold in space” (B162). We must accept further the conclusion of the Transcendental Aesthetic, which is based on arguments that we have found suspect. We must accept the conclusion of the “manifold” part of the deduction, according to which there is an intellectual synthesis subject to pure concepts of the understanding.

But even if we accept all of this, there is still step 7 to contend with. The conclusion of §20 was that we refer the unity resulting from the intellectual synthesis to the unity of consciousness through the application of the categories in judgment. This is a somewhat plausible view. It does not, however, appear to entail that what governs the intellectual synthesis also governs the figurative synthesis. Why is it that when one draws a figure in space or presents two events as one succeeding the other in time, a pure category is involved?

Perhaps an answer can be found in the appeal to specific cases. After presenting the “synthesis” argument of §26, Kant gives two examples of how categories play a role in the figurative synthesis. The first example, drawing a house’s shape, takes place under the guidance of the category of magnitude. “This same unity, if I abstract from the form of space, resides in the understanding, and is the category of the synthesis of the homogenous in an intuition as such, i.e., the category of magnitude. Hence, the synthesis of apprehension, i.e., perception, must conform throughout to that category” (B162). One might say, then, that the categories of quantity (“magnitude” is not listed in the table of categories) is required for the presentation of any figure, and so is involved in any synthesis of a perception of an object in space. This argument is similar to that in the Aesthetic where Kant claimed that space and time remain when abstraction is made of all the empirical elements in perception (A20-21/B34-35).

A second example Kant gives is the presentation of a state of water as liquid and the presentation of it as solid, in freezing. Time is at the basis of this perception, and determinate location in time can be given only if the sequence of presentations is unified. Kant claims here that what unifies the presentations is a principle: “everything that happens is, in terms of its relation, determined by me in time as such” (B163). This principle, in turn, is applied to sensibility through the category of cause. Kant would only later, in the Second Analogy, argue that the determination of events in time requires appeal to causality.

If this interpretation is correct, then the Transcendental Deduction does not stand on its own, even if the “deduction” of space and time are folded into it. In order to show that the figurative synthesis is really subject to rules involving the categories, Kant must show how each of the categories is essentially involved in some aspect of the figurative synthesis. This is the work of Book II of the Transcendental Analytic, the Analytic of Principles.

Laws of Nature

The deduction is supposed to show that all objects of perception, and therefore all objects of experience (which is connected perception), are subject to categories. These objects are one and all appearances, objects of sensible intuition. It is a very short step to the claim that nature itself is subject to the categories, as “concepts that prescribe laws a priori to appearances and hence to nature regarded as the sum of all appearances” (B163). After making this claim, Kant asks how it is possible, given that the categories are not empirical, not derived from experience.

The groundwork for the answer to this question has already been laid in the Aesthetic. Nature must conform to the forms of space and time, which are a priori contributions of human intuition. They do so only insofar as they are appearances, which “exist not in themselves but only relatively to the subject in whom the appearances inhere insofar as the subject has senses” (B164). Analogously, the laws of nature are contributions of human understanding and apply to nature only insofar as it is the sum of appearances. “Things in themselves would have their law-governedness necessarily, even apart from an understanding that cognizes them. But appearances are only presentations of things that exist uncognized as regards what they may be in themselves” (B164).

The rest of the argument is as expected. Appearances are subject to the law of the power that connects them. What connects them is the imagination, whose transcendental synthesis depends on the categories. “Therefore all possible perceptions, and hence also everything whatever that can reach empirical consciousness, i.e., all appearances of nature, must in regard to their combination be subject to the categories” (B165). Particular laws of nature, on the other hand, though they must conform to the categories, depend on the empirical content of perception.

Objects must conform to our a priori forms of intuitions and concepts. In Book II, Kant will show specifically how this is the case. The opposite view, that concepts must conform to objects, is rejected out of hand. A possible compromise, which has the fingerprints of Leibniz on it, is also rejected. This is a “preformation system,” according to which our a priori concepts are implanted in us by God, and the world is so arranged by God as to conform to them.

This view leads directly to skepticism, because it implies only a subjective necessity. It may be that I cannot think objects otherwise than through the categories because that is the way I am made. But this does not show that the objects themselves must conform to them. We would lose not only the claim to objective validity, but even the subjective necessity of the categories, insofar as some people would profess not to think through them.

The chapter concludes with a “brief sketch” of what has been accomplished in the deduction. The categories have been shown to be principles of the possibility of experience. Appearances in space and time are determined by the categories. And finally, the source of the determination is “the original synthetic unity of apperception, this unity being the form of understanding as referred to space and time, the original forms of sensibility” (B169).

New Vocabulary

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