The expositions of the concept of time follows fairly closely those of space. Kant's goal in the metaphysical exposition is to show that the presentation of time is not an empirical concept or a discursive concept, but rather is a “pure form of sensible intuition” (A31-2/B47). The arguments he presents are structurally the same as the arguments purporting to prove the same results for the concept of time. As such, these arguments are subject to the same criticisms as given in the last lecture.
The only new wrinkle is in item 4, which contains the argument that different parts of time are possible only through a single object, which must then be an intuition. Kant adds a second argument. If time were a universal concept, then the fact that different times cannot be simultaneous could not be proved by analysis of the concept, since it is a synthetic principle. Kant tells us that this principle is “contained directly in the intuition and presentation of time” (A32/B47). Presumably we can, as it were, just see that it is true by examining the presentation of time.
Another argument unique to time can be found later, in §6. Kant notes that we can present a sequence of time using the spatial analogy of a line. He draws the conclusion that the presentation of time is an intuition from the fact that it can be presented in space, which has already been established as an intuition. “This fact, . . . , that all relations of time can be expressed by means of outer intuition, shows that the presentation of time is itself an intuition” (A33/B50).
The transcendental exposition of the concept of time is given in item 3. This reflects the structure of the first edition. The corresponding item 3 in the first-edition exposition of the concept of space was replaced by a new section, §3. In the treatment of time, the old item 3 is preserved, with the apology that “for the sake of brevity” it was put among the items that strictly speaking belong to the metaphysical exposition.
Recall that the purpose of a transcendental exposition of a concept is to show how synthetic principles may be based on it a priori. For space, these principles are those of geometry. Time has its own special “axioms of time in general” (A31/B47). Among these are that time is one-dimensional and that unlike the parts of space, which exist simultaneously, the parts of time exist only sequentially.
In §5, which was added to the second edition, Kant adds some further principles which depend on time as the form of intuition. These are the concepts of change and motion. Without the presentation of time, we would never be able to form these concepts at all. A change is the combination of two opposed predicates in the same object, something that is forbidden by the principle of contradiction if we cannot assign the having of these predicates to different times. Motion is change of place, so its concept depends on the intuition of time as well.
One of the most striking differences between the Critique and the Prolegomena is that the a priori principles said to be supported by time in the latter work are those of arithmetic. “Arithmetic attains its concepts of numbers by the successive addition of units in time” (§10, Ak 4:283). This claim is hinted at in the second-edition Introduction, where Kant appeals to the use of five fingers to add five to seven in order to arrive at twelve. “Thus, in that image of mine, I gradually add to the number 7 the units that I previously gather together in order to make up the number 5. In this way I see the number 5 arise” (B15-16). It is not clear why Kant did not claim in the Aesthetic that arithmetic ultimately is founded on the presentation of time.
As with space, time is said not to be “a determination or order attaching to things themselves” (A32/B49). The argument for this negative claim with respect to time is quite similar to that with respect to space, which reads, “For determinations, whether absolute or relative, cannot be intuited prior to the existence of the things to which they belong, and hence cannot be intuited a priori” (A26/B42). The corresponding argument in the section on time is this: “If . . . time were a determination or order attaching to things in themselves, then it could not precede the objects as their condition, and could not a priori be cognized therough synthetic propositions and intuited” (A33/B49).
In the section on time, Kant contrasts time as a determination or relation of things in themselves with time as a self-subsistent being. He then gives this argument against the doctrine that time is a self-subsistent being: “For if time were self subsistent, then it would be something that without there being an actual object would yet be actual” (A32/B49). This is similar to the argument found in a passage in the General Comments that was added in the second edition. (This argument was discussed in the previous lecture.) Unlike the argument against time as an order of things, which invokes the a priori intuition of time, this one claims that the notion of time as self-sufficient is conceptually incoherent.
As with space, we are told that the only viable account of time is that it is only a ”subjective condition" which makes intuition possible. The a priori presentation of space is only a condition for outer intuition, the presentation of spatial objects through the senses. In contrast, the a priori presentation of time is a requirement for all intuition, inner and outer. (Inner intuition is the presentation of our “empirical self,” that is, our mind as it is given to itself, as an object.) Our inner self is presented only in time, while outer objects are presented in space and time.
As with the consequence for space, it seems that the consequence for time outstrips the conclusion of Kant's argument. Suppose we cannot intuit an object as being in time unless there is already in us a presentation of time itself. This does not, on the face of it, imply that, “Time is nothing but the form of inner sense, i.e. of the intuiting we do of ourselves and of our inner state” (A33/B49). To draw this conclusion, we would have to have a reason to think that the presentation of time is identical to time itself.
Another question that arises is why time is a form of inner intuition alone, and not of both inner and outer intuition, “nothing but the form of inner sense.” Kant's answer is this: “For time cannot be a determination of outer appearances, [because] it does not belong to any shape or position, etc., but rather determines the relation of presentations in our inner state” (A33/B49-50). One might ask why outer sense can detect only spatial properties and not temporal succession.
The answer seems to be that temporal succession can only be presented in a succession of presentations. A succession of presentations is given to us as a succession only when we intuit that succession. But this does not mean that only objects of inner intuition are presented as in time. Objects of outer intuition are presented temporally as well, only indirectly. “But all presentations, whether or not they have outer things as their objects, do yet in themselves, as determinations of the mind, belong to our inner state; and this inner state is subject to the formal condition of inner intuition, and hence to the condition of time” (A34/B50).
Kant claimed that time is ideal in the same sense in which space is ideal. Time does not “attach to things absolutely, as a condition or property” (A36/B52). It is “nothing” “if we abstract from the conditions of sensible intuition” (A36/B52). Thus time is a feature of appearances but not things “as such.” It “has objective validity only with regard to appearances, because these are already things considered as objects of our senses” (A34/B51).