• The doctrine of transcendental idealism
  • Transcendental ideality and empirical reality: the empirical/ transcendental distinction
• Kant’s ontological denial
• The argument for transcendental idealism in the Aesthetic
  • The four salient arguments
  • A problem with geometry
  • A different argument
• Trendelenburg’s alternative
• The argument for transcendental idealism in the Antinomy

Both Newton and Leibniz’s view of space and time is that they are contained in the world independent of the subject’s awareness, and that we have representations of space and time because we have knowledge of reality. That is what Kant denies. Kant formulates it by saying that space and time, and objects with spatial and temporal properties, are transcendentally ideal. The first two sections of this chapter aim to explain what Kant means by this claim, and those that follow consider his defense of it.

The doctrine of transcendental idealism

The basis of the doctrine of transcendental idealism is the distinction of appearance and thing in itself. A thing considered as necessarily conforming to our mode of cognition is an appearance (transcendentally ideal), and a thing to which our cognition must conform is a thing in itself (transcendentally real). Human sensibility, Kant has argued, is distinguished by spatio-temporality, and since they are the only objects given to us, all objects for us are appearances (transcendentally ideal).

Transcendental ideality and empirical reality: the empirical/ transcendental distinction

That the objects of our cognition are transcendentally ideal provides, according to Kant, the basis for the further claim that they are at the same time empirically real. The empirical/transcendental distinction originates with Kant, and is best grasped in terms of different standpoints from which things may be considered in philosophical reflection, the same object can be considered in both empirical and transcendental respects.

To consider things in empirical respects is to consider them from the human standpoint, as appearances. The term empirical retains here its original connection with sensation, since the human standpoint is one of being related to objects through sensation.

To consider things in transcendental respects is to consider them from the standpoint of enquiry into the conditions under which objects are possible for us. The transcendental standpoint differs from the human standpoint in that it considers things in relation to our mode of cognition, without considering them merely as they appear to us through our mode of cognition, as does common sense. The transcendental standpoint allows the dependence of objects on our mode of cognition to be determined.

Kant’s ontological denial

Kant claims not only that we cannot know that things in themselves are spatial-temporal, but we can know that they are not spatial-temporal. Kant indicates that space and time belong only to the form of intuition and could not be ascribed to anything apart from the subjective constitution of our mind. We can make claims about things in themselves because Kant’s claim about things in themselves is that we cannot have contentful positive knowledge of them, since they cannot become objects for us; but we can have negative contentless knowledge of them, given the result that space and time are only forms of sensibility.

The argument for transcendental idealism in the Aesthetic

The four salient arguments

1. Geometry tells us not just what the spatial properties of the objects of our experience happen to be, but what they must be. Now if the objects described by geometry were things in themselves, then they would have their geometrical properties not by virtue of our sensibility but by virtue of how they are independently of us. But in that case we can’t have necessary knowledge for judgments like “two straight lines can’t enclose a space”, because necessities inhering in things in themselves cannot simply migrate into our minds, we can only come to know them through some sort of contact with things in themselves, i.e. through experience, but experience can’t provide us with knowledge of necessity.

2. The result of regarding space and time as “properties which, if they are to be possible at all, must be found in things in themselves”, is to transform everything in our experience into “mere illusion”. That is, if we take the transcendental realist view of space and time as absolutely real objects, then we are obliged to suppose that our cognitive powers are capable of knowing two infinite and yet non-substantial things, and this, Kant thinks, is an absurdity which will drive us to Berkeley’s conclusion that the concepts of space and time really refer to what is given immediately in experience, namely mere seemings.

3. Space and time consist in nothing but relations, and that things in themselves cannot be constitutionally merely relational, from which it follows that space and time, and spatio-temporal objects, cannot be things in themselves

4. If God is to be at least conceivable (whether or not God exists), then space and time must be regarded as transcendentally ideal; for if they were transcendentally real, they would be conditions of God’s existence, which would make it impossible for God (whose intuition is non-sensible) to know himself, contradicting the concept of God as an omniscient being.

A problem with geometry

The view most commonly taken is that only the argument from geometry has a chance of succeeding. However, even if Kant is justified in claiming that transcendental realism is incompatible with the necessity of geometry, developments in geometry have undermined the argument’s premises. Modern physics shows that Euclidean geometry, though approximately tree, is strictly false, the correct description of space being given by non-Euclidean geometries, and because it is therefore an empirical question what geometry best fits physical space, Kant is wrong to suppose that geometry is a priori and necessary - it is in fact a posteriori and contingent.

However, transcendental idealism does not imply that space is necessarily Euclidean. Space has two concepts: transcendental and empirical. The former is the representation of space which Kant has argued to be an a priori intuition and transcendentally idea.

A different argument

The underlying argument for transcendental idealism in the Aesthetic can be expressed as follows:

1. It must be explained how objects are possible for us.
2. Transcendental realism cannot explain how objects are possible for us.
3. The possibility of objects for us is explained by supposing that we have a priori representations that constitute objects.
4. The possibility of objects for us requires that they be conceived as transcendentally ideal.

Kant’s reason for making necessity the criterion of a priority is that the necessity of some feature of objects signals a respect in which they conform to the structure of experience and hence qualifies as an a priori feature.

Trendelenburg’s alternative

There is a famous objection from Trendelenburg:

even if we concede the argument that space and time are demonstrated to be subjective conditions which, in us, precede perception and experience, there is still no word of proof to show that they cannot at the same time be objective forms.

According to Trendelenburg, Kant has been supposing that space and time are either forms of sensibility or real existences, but another alternative is that they are both.

However, I think the problem is “objective form” is meaningless without the human perspective.

The argument for transcendental idealism in the Antinomy

Kant’s argument, very briefly, is that the contradictions of transcendent metaphysics are logically unavoidable from the standpoint of transcendental realism. The specific contradictions that he has in mind concern the spatio-temporality and other essential features of the empirical world.

To take the first of the four that Kant examines: Kant argues that if we suppose space and time to characterize things in themselves, then we are committed to affirming both that the world is unlimited in space and time past and that it is limited in space and has a beginning in time. Now this is a reductio ad absurdum: whatever entails a contradiction must be false. By inferring the falsity of transcendental realism, we have a proof of transcendental idealism. Indeed, transcendental idealism in its stronger form would be proven, for the argument, if successful, would show that it is impossible for things in themselves to be characterized by space and time.

This will be discussed in more detail in chapter 7.

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