Kant was always on the defensive regarding his transcendental idealism. Historically, realism has been the default philosophical position, and if idealism is not simply dismissed outright, strong arguments are demanded to give it any credibility at all. The earliest reviewers of the Critique made Kant’s idealism their main target in their criticism of the work. (For Kant’s account of this criticism, see the Appendix to the Prolegomena, at Ak 4:371ff.) Kant’s contemporary F. H. Jacobi remarked that Kant could not live without the thing in itself, but at the same time could not live with it. Moreover, it is far from certain what the doctrine even is. Scholars are still debating the real meaning of transcendental idealism. It is one of the most difficult interpretive problems in all of Kant, rivaled only by the interpretation of the Transcendental Deduction.
Transcendental idealism is fundamentally a doctrine about space and time, and derivatively a doctrine about things in space and time. We might begin our examination of it by noting what Kant says that space and time are not. Our initial discussion will draw on the first six sections of the Aesthetic.
The first claim is that space and time are not self-subsistent objects. This is a denial of the Newtonian account of “absolute” space and time. In some sense, space and time are relative. One sense in which they might be relative is as relational properties or relations of self-subsistent objects. This was the Leibnizian view.
Here the expression “self-subsistent” expresses a contrast with what does not exist on its own: a property or a relation. Traditionally, an object that is self-subsistent in this way is called a substance. When Leibniz declared space and time to be relative, he at least meant that they are not substances. The Newtonian view was, as Kant recognized, somewhat odd in this respect, because absolute space and time are not really substances, things with properties. They are instead independent beings of a peculiar sort.
Kant regarded the debate between Newton and Leibniz as sterile. The two sides shared a common assumption, namely, that space and time “would remain if one abstracted from all subjective conditions of our intuition of it” (A32/B49). The Leibnizian view regards space and time as “determinations or relations that would belong to things intrinsically also, i.e., even if these things are not intuited” (A23/B37). Yet another way of describing what leads to the assumption is that “we abstract from the sensibility of our intuition, and hence from the way of presenting peculiar to us, and speak of things as such” (A35/B51). If the abstraction is made, and we are concerned with things as such, there is nothing to dispute. Space and time have nothing to do with such objects.
Another way of saying that space and time do not belong to things “intrinsically,” is to say that they do not belong to them “absolutely,” that is, apart from any relations, and specifically apart from their relations to sensible intuition. “We dispute any claim whereby time would, quite without taking into account the form of our sensible intuition, attach to things absolutely” (A35-6/B52). If they did, they would be “properties belonging to things in themselves” (A36/B52). Instead, space and time are forms of human sensibility, and the objects to which they apply are appearances.
The expression “things in themselves” is intended to be contrastive: things in themselves are things “apart from their relation to our intuition” (A36/B52). We think of things in themselves only insofar as we abstract from this relation. This suggests that we have a base conception of spatio-temporal objects of our sensible intuitions, appearances, and that we attempt to think conceptually of those very things independently of the way they are intuited.
This is how Kant described the matter in an oft-quoted passage from §7.
Appearance always has two sides. One is the side where the object is regarded in itself (without regard to the way in which it is intuited, which is precisely why its character always remains problematic). The other is the side where we take account of the form of the intuition of this object. This form must be sought not in the object in itself, but in the subject to whom the object appears. (A38/B55)(It should be noted here that some commentators think that Kant regarded appearances and things in themselves as distinct objects. We shall not pursue that line of interpretation here.) As for the “problematic” character of things in themselves, Kant says in §8 that, “What may be the case regarding objects in themselves and apart from all this receptivity of our sensibility remains entirely unknown (unbekannt). All we know is the way in which we perceive them” (A42/B59).
This passage revives a puzzle that was raised in our discussion of the ideality of space. The passage just quoted expresses skepticism about the character of things in themselves. But in the very same paragraph, Kant stated that, “The things that we intuit are not in themselves what we intuit them to be” (A42/B59). To maintain consistency, we shall take the “unknowability” claim to mean that although we know what things in themselves are not (spatio-temporal), we do not know what they are.
The claim that we know that things in themselves are not spatio-temporal appears dogmatic. How could Kant argue for it without violating his critical method? Kant’s contemporary Reinhold pointed to a “neglected alternative” between spatial appearances and non-spatial things in themselves, i.e. that things in themselves may be spatial although we could never establish that they are. Whether this alternative holds seems to be something about which an investigation of a priori cognitions could not determine.
So the first argument for the non-spatio-temporality of things in themselves looks to be defective. The fact that objects are and must be presented to human sensibility as spatio-temporal does not imply that they would not be spatio-temporal if considered apart from their relation to human sensibility. Perhaps we can find a better argument for this conclusion.
In §8, Kant makes an observation which he claims allows his theory to “be confirmed superbly” (A49/B66). The observation is that all spatio-temporal properties are purely relational.
Whatever in our cognition belongs to intuition . . . contains nothing but mere relations: of places in an intuition (extension), of change of places (motion), and of the laws according to which this change is determined (motive forces). (A49/B66-7)We cannot, “of course,” cognize a thing in itself through mere relations. So our outer intuition can never reveal “the intrinsic character belonging to the object in itself” (A49/B67). Instead, all that is revealed in sensible intuition is “the relation of an object to the subject.”
Let us grant that through mere relations we can never characterize a self-subsistent object, since as Leibniz recognized, substances are metaphysically more basic than the relations in which they stand. To make the argument work, Kant would have to claim that things in themselves are self-subsisting objects. This may seem to run afoul of the claim that we do not know anything about things in themselves (aside from their not being spatio-temporal, which is at issue here).
But the very concept of a thing in itself as a thing abstracted from its relation to sensibility implies that we know at least this much, that they are things that do stand in relation to human intuition. Now given the metaphysical principle that what stands in a relation to another thing is self-subsistent, Kant can get the conclusion that things in themselves are self-subsisting objects (though we know nothing of what their properties are, other than that they affect the human mind).
Still, the argument is not convincing. We have granted that we cannot use relational properties to characterize a thing in itself insofar as it is a self-subsisting being. But this is not to say that such a being cannot have relational properties or stand in relations. It does stand in a relation to the human mind, after all. So it still may be, for all we know, that if we abstract from that relation, these things stand in spatio-temporal relations to one another.
We might be able to piece together a better argument from the material in the Amphiboly and the Aesthetic. Its basic structure is this:
In the Amphiboly, Kant explicitly endorsed step 5, on the grounds that for an object of the pure understanding, the “matter” must be more basic than the “form.”
Hence in pure understanding’s concept matter precedes form; and because of this Leibniz first assumed things (monads) and within them a power of presentation on their part, in order then to base thereon their extrinsic relation and the community of their states (viz., the community of their presentations). Hence space and time were possible as bases and consequences—space only through the relation of substances, time through the connection of their determinations among one another. And thus it would in fact have to be, if pure understanding could be referred directly to objects, and if space and time were determinations of things as they are in themselves (der Dinge an sich selbst). (A267/B323)The backing for step 2 comes from the Aesthetic, most importantly in the claim that a thing cannot be referred to a location in space or time without there being a space and time in which to locate them (A23/B38, A30/B46).
We have already pointed out that the claim embodied in step 2 needs further justification. Merely to assert it is to beg the question against Leibniz and those who hold a relational concept of space. Step 5 faces a familiar problem. Even supposing that it must hold for objects of a pure understanding, we still need a reason to think that objects of pure understanding would be things as they are in themselves. To be sure, this a fundamental assumption of rationalism, but Kant ought to have given it some justification.
In §8, “General Comments,” Kant makes a different case for the transcendental ideality of space and time. He claims that if our presentations of space and time have their origin in things in themselves, rather than in human sensibility, we would not be able to make synthetic judgments of mathematics a priori. Since we can and do make such judgments, our presentations must have an origin in us. Moreover, the judgments apply only to appearances, i.e., to things as presented to human sensibility. From this, he draws the “indubitably certain” conclusion:
Space and time, as the necessary conditions of all (outer and inner) experience, are merely subjective conditions of all our intuition. Hence in relation to these conditions all objects are mere appearances, and are not given to us in this way on our own. And that is why much can be said a priori about these objects as regards their form, but not the least can ever be said about the thing in itself that may underlie these appearances. (A48-9/B66).
This is probably the best-known argument for the transcendental ideality of space and time. Given that we make synthetic judgments a priori about the spatio-temporal properties of objects, the basis of these judgments could only lie in the human mind. Since space and time are not concepts, they are intuited, and they must be intuited a priori. The objects to which they apply can only be objects that must conform to our a priori intuitions, and so they are appearances.
The primary objection to this argument is that synthetic mathematical judgments made a priori need only apply to special objects of mathematics: geometrical figures, numbers, etc. But why must they also apply to the sensuous objects of human experience? Even if Kant’s way is the only way to explain how they do, perhaps they do not. It is often charged, for example, that Kant thought that Euclidean geometry is known a priori to be true, but the empirical investigations of physics have shown that the geometry of the universe is not Euclidean.
So far, we have been making the case that Kant did not justify his denial of the spatio-temporality of things in themselves. We shall now take up an objection that states that things in themselves must be temporal on Kant’s own grounds. This objection was raised by Lambert. Here is how he put it in a letter to Kant of October 13, 1770, shortly after the publication of the Inaugural Dissertation.
All changes are bound to time and are inconceivable without time. If changes are real, then time is real, whatever it may be. If time is unreal, then no changes are real. I think, though, that even an idealist must grant at least that changes really exist and occur in his representations, for example, their beginning and ending. Thus time cannot be regarded as something unreal. . . . Since I cannot deny reality to changes, until somebody teaches me otherwise, I cannot also say that time (and this is true of space as well) is only a helpful device for human representation.The criticism is reiterated in §7 of the Aesthetic, entitled “Elucidation.” Its conclusion, as stated there, does not go as far as Lambert’s original. It states only that “time is something actual” (A37/B53).
Kant’s response to the criticism was to “concede the whole argument” (A37/B53).
Time is indeed something actual, viz., the actual form of inner intuition. It therefore has subjective validity in regard to inner experience; i.e., I actually have the presentation of time and of my determinations in time. Hence time is to be regarded as actual, though not as an object but as the way of presenting that I myself have as an object. (A37/B53-4)Thus, Kant’s response is to concede the actuality of time, but only in the limited sense of a way of presenting one’s internal states.
This response is suspect. Suppose we grant that we must actually present our mental states as changing in time. We can still ask about the presenting itself. If I present my mental state as now one way and then present my mental state as another way, it would seem that there are two presentations. So, it seems that there is change in the mind in the presenting, not just in what is presented. Real change in time seems to be presupposed by the presentation of states as changing in time. It would do no good to say that we present the mind as successively presenting states in time, for this leads to a regress.
The contemporary American Kant scholar Henry Allison, in the first edition of his Kant’s Transcendental Idealism, has defended Kant against the classical objections that I have been presenting here. He claims that they all rely on an “ontological” reading of the distinction between appearances and things in themselves (see, for example, Kant’s Transcendental Idealism, first edition, Chapter 1). A thing in itself, on this reading, is a thing as it is independently of a real relation to human sensibility. An appearance, on the other hand, is a thing as it stands in a real relation to sensibility.
Allison invites us instead to consider an “epistemological” reading of the distinction. An appearance is an object as it is known by us, whereas we think a thing in itself by beginning with a known object and considering it in abstraction from the conditions under which we know it (what Allison calls “epistemic conditions”). Our conception of a thing in itself is necessarily very thin: that of an unknown X which there must be in order for something to appear. Kant claims that, “We must be able at least to think, even if not cognize, the same objects as things in themselves. For otherwise an absurd proposition would follow, viz., that there is an appearance without anything that appears” (Bxxvi-xxvii).
If we dispense with the ontological reading in favor of the epistemological reading, the puzzles we have been raising can be dissolved. The first puzzle was how Kant could claim, apparently dogmatically, that things in themselves are not spatio-temporal. If being spatio-temporal is merely a condition of knowledge, then necessarily when we abstract from the condition of knowledge, the X which remains is not spatio-temporal. (Of course, it would remain for Kant to establish that space and time are merely conditions of knowledge.)
Lambert’s objection can be dealt with similarly. We can say that time is real in the sense that it is a real condition of human knowledge. And this is all we need to say, since to view the reality of time in any other way would be to adopt the ontological standpoint that has been ruled out.
Allison’s defense is an attractive way of getting around the objections that have been raised here. But it depends on giving all of Kant’s pronouncements about appearances and things in themselves a single very conservative reading. We are forced to understand Kant’s frequent talk of “the real per se” and “things as they are in themselves” as not being about what they appear to be about.
And what are we to make of Kant’s claim in the Amphiboly about how things in themselves must be for the pure understanding, if they are merely a residue X left over when the conditions of knowledge are removed from the consideration of a thing that appears? Another problem might be this. If the reason for denying that things in themselves are not spatial or temporal is as simple as the one Allison presents, why did not Kant explicitly state it himself? Why, for example, did he mobilize the argument that spatial properties consist of nothing but mere relations?
My own view is that the “relation to sensibility” of a thing was for Kant a real relation, a relation which involves among other things the fact that the object affects the mind in a certain way. Presentation is a real activity of the human mind. This is not to say that Kant did not have an epistemological conception of the relation to sensibility and presentation as well. He appears to have had both, which is the main reason why his doctrine of things in themselves is so difficult to untangle.