In the last lecture on Kant’s philosophy we described it as a revolution in the history of philosophy and a complete reversal of the previous way of understanding our knowledge of the world. This revolution bears a name, and it is a name that Kant himself gave to it: the Copernican revolution.
Hitherto it has been assumed that all our knowledge must conform to objects. But all our attempts to extend our knowledge of objects by establishing something in regard to them a priori, by means of concepts, have, on this assumption, ended in failure. We must therefore make trial whether we may not have more success in the tasks of metaphysics, if we suppose that objects must conform to our knowledge […] We should then be proceeding on the lines of Copernicus’ primary hypothesis. [Bxvi]
We can understand what this revolution might mean by comparing it to what Kant believed needed to be rejected if we were to give a secure foundation to our knowledge of the world, namely dogmatic metaphysics.
It is opposed only to dogmatism, that is, to the presumption that is possible to make progress with pure knowledge, according to principles, from concepts alone (those that are philosophical), as reason has long been in the habit of doing; and that it is possible to do this without having first investigated in what way and by what right reason has come into possession of these concepts. [Bxxxv]
The test for whether metaphysics is valid or not for Kant is experience. As he writes in the first sentences of the introduction of The Critique of Pure Reason, knowledge begins with our experience of the world, and without this limitation of experience, there would be no brake to our imaginative production of concepts [B1]. For Kant, however, this is precisely where classical, as opposed to critical philosophy, has erred. For it has believed that the principle of a philosophical method is to be determined to the extent that it rejects reality for the ethereal realm of pure ideas, which Kant rather picturesquely describes in the image of the flight of a dove and associates with the name of Plato:
The light dove, cleaving the air in her free flight, and feeling its resistance, might imagine that its flight would be still easier in empty space. It was thus that Plato left the world of the senses, as setting too narrow limits to the understanding, and ventured out beyond it on the wings of the ideas, in the empty space of the understanding. [A5/B9].
But if our experience of the world is the test for the validity of our philosophical method, why is Kant simply not an empiricist, rather than a transcendental idealist as we described last week, and does this not contradict the meaning and import of the Copernican revolution that asserts that the world must conform to us, rather than we to the world? The solution to this contradiction is to see that for Kant experience is not all that it seems to be. Or to put it another way, and this is perhaps the central paradox in Kant’s thought, there is more within experience than merely experience.
Kant’s proof for this is indirect. His claim is that if we simply assert that all knowledge is empirical, then we are denying any possibility of any a priori nature of own knowledge. What Kant means by the a priori is that which is independent from our knowledge of the world that is arrived at through our senses, which can be defined in contradistinction as a posteriori knowledge. The examples of a priori knowledge that Kant gives are mathematics and physics (we shall look at the details of this argument in the next week). I know that a triangle must have three sides without having to test this empirically. I also know that everything in nature has a cause without having to test the hypothesis experimentally. The criterion for the difference between a priori and a posteriori knowledge is necessity and universality [B3-4]. For this reason we should not confuse what is a priori with an empirical law, for the latter rests only on observation and there is no absolute certainty that an event could be otherwise or a different theory could be used to explain its significance, whereas without the category of causality we could not make sense of the notion of ‘event’ at all; the world would be meaningless for us.
Since what is a priori cannot come from experience, since nothing from experience can happen from necessity, then it must have another source. This other origin is the subject. Kant writes, ‘that we can know a priori of things only what we ourselves put into them’ [Bxviii]. Why, therefore, are these a priori principles not merely subjective fantasies? Why is not Hume right to suggest that causality, for example, is merely a subjective representation that is simply the habitual way that we look at the world, and is not an a priori necessity of our knowledge of the world? Kant’s position is not that far from Hume, as Broad is right to point out, but his disagreement with Hume is that we could not choose not to look at the world in this way (Broad 1978, p.13). Thus we come to a second paradox of Kant’s thought: not all that is in the subject is merely subjective.
To see why it is not merely subjective we need to clarify certain terminological distinctions. When Kant speaks about the difference between appearance and thing in itself, this should not be modelled on difference between what is merely subjective on the one hand, and what is objective on the other, as we might say, for example, using that old Platonic example, that the stick appears bent in the water, but the real stick is not. This would be to distort Kant’s distinction between appearance and thing in itself in the classical distinction between appearance and essence. The difference between the classical and critical philosophy, is that the former opposes the sensible and intelligible realms, whereas the latter places the intelligible within the sensible. To understand what Kant means by appearance is to see that the distinction between form and matter is internal to it. It is not, as in the classical picture, that form equals essence, and appearance matter. Kant would say, on the contrary, that it is the form of appearance that is a priori and comes from the subject, whereas the matter is given by experience and is a posteriori.
To confuse the form of appearance with the matter of appearance is to confuse transcendental idealism with empirical idealism and is to mistake Kant’s project with his predecessors. For it precisely to avoid empirical idealism that Kant invents transcendental idealism. We need to distinguish four possible positions of epistemology to be able to determine the true nature of transcendental idealism. They are:
- Transcendental Realism
- Empirical idealism
- Transcendental idealism
- Empirical realism.
For Kant there four positions always come in pair. Thus if you are an empirical idealist, it necessarily follows that you are an transcendental realist, and if you are empirical realist, then it also necessarily follows that you are a transcendental idealist. How can we explain these terms in greater detail? First of all we need to understand that the meaning of ‘real’ and ‘ideal’ change when we are describing them in a transcendental or empirical way, and much of the confusion about Kant lies in misunderstanding these subtle differences. Following Allison, we can define ideality as being part of consciousness, and reality as being independent or outside of consciousness (Allison 2004, p.6). From an empirical standpoint, what is ideal is the private datum of the individual consciousness, whilst what is empirical is, to use Allison’s expression, ‘the intersubjective, spatiotemporal realm of the objects of human experience.’ Where we might go wrong is when we take this empirical definition and simply transpose it to the transcendental sphere. Thus, we confuse transcendental idealism with empirical idealism. It is this confusion that might make us think that the a priori, in Kant’s sense, is merely subjective; in other words that it simply an idea in our minds. How then can we make sense of the distinction between the ideal and the real in a transcendental manner? What are transcendentally ideal are the a priori conditions of human empirical knowledge, and what is transcendentally real is that which is independent of these conditions; that is to say non-sensible objects. What is important to underline here is that transcendental idealism does not speak of the content of experience, but of the conditions of experiences. Its object is not what we know, but how we know.
Kant, therefore, is an empirical realist. Objects are independent of the individual consciousness but a transcendental idealist, that the form of knowledge is the condition for these objects. It is important not to confuse transcendental idealism with psychology. Psychology is an empirical science that begins with individual consciousness from which by a process of induction, like any other natural science, it arrives at universal laws. Universal laws of nature, however, are not the same as a priori conditions of knowledge, for the former are contingent and the latter are necessary for the representation of any object. Psychology can tell us why we see this particular object in this way, or react to this situation in this way, but it cannot provide us with the description of the object in general (how every object must be formed to be a sense object, or an object of judgement), for it too must begin with this general object as a presupposition.
As we have said, it is Kant’s argument that empirical idealism always leads to transcendental realism. We have already seen this to be the case with Descartes. If I say that all I can truly know are my representations of things in my mind, then I am claiming that reality of objects is independent of my consciousness and I cannot know them. This further entails, as we have already recognised, that only God can know the reality of things. Transcendental realism is therefore theocentric. We might, therefore, characterise Kant’s Copernican revolution as anthropocentric. All we can know is that which remains within the limits of human knowledge, what is given to us in experience, and what is ideal is merely the form of this experience whose source is the structure of human subjectivity in general.
Allison, H.E., 2004. Kant’s Transcendental Idealism, New Haven: Yale University Press.
Broad, C.D., 1978. Kant : an Introduction, Cambridge; New York: Cambridge University Press.
Pippin, R.B., 1982. Kant’s Theory of Form : an Essay on the Critique of Pure Reason, New Haven: Yale University Press.
. He is wrong, however, to suggest that Kant has advanced no further than Hume in this problem.
 What follows owes much to Allison’s account in Kant’s Transcendental Idealism (Allison 2004, pp.1–35).
 This is why the notion of ‘form’ is central to Pippen’s understanding of Kant’s project in Kant’s Theory of Form (Pippin 1982, pp.1–25).