is accepted as the correct conception of the relationship between ourselves and the objects of our hoped-for mathematical and natural scientific knowledge, then, as Kant realized, there would be no possibility of our acquiring any informative universal or necessary knowledge of these objects. At best, what we could hope to acquire would be empirical, hence only probable, knowledge. On the other hand, if we adopt the revolutionary point of view that the objects that we are seeking to learn about by means of our faculties of knowledge must themselves conform to those very faculties in order to become objects of the senses, then we might well be able to acquire some genuinely necessary and universal knowledge of objects as possible objects of the senses.For, independently of our acquiring any experience of these objects, we might be able to discover, by investigating our own faculties of knowledge, what conditions these faculties impose on the possibility of our experience and its objects.
In effect, the first major task that Kant sets himself, in the main body of the First Critique, is to show that his revolutionary way of conceiving the relationship between ourselves and the objects of our sensible knowledge – viz. that these objects must accord with our faculties of knowledge, rather than the traditional picture of trusting that our faculties of knowledge will be in accord with its sought-for objects – is, indeed, the correct one. This he seeks to accomplish by establishing two claims: first, that the dimensions in which the objects of our senses are located – namely, in space and in time – are dependent on us (are, in fact, properties of our mind); and second, that the fundamental laws governing the behaviour of the objects of our senses are dependent on concepts existing innately in us. If both of these conditions can be made out, it can be said that the whole framework by means of which objects of the senses can be known – the sensuous forms in which they are given (space and time) and the basic dynamical laws governing them – will be contributed by us. Clearly, such a picture of our relationship with the objects of our sought-after sensible knowledge is a far cry from the traditional one.
The revolutionary point of view according to which the objects of our senses should be taken to conform to our faculties for acquiring knowledge, Kant likens to Copernicus’s revolutionary hypothesis concerning the spectator of the heavens and the heavenly bodies. On the traditional conception of the latter relationship, the spectator is at rest, and the observed behaviour of the heavenly bodies is dependent on their movement alone. On the Copernican hypothesis, the observed behaviour of the heavenly bodies depends, in part, upon the movement of the spectator. This hypothesis, Kant wishes to say, was firmly established on two grounds. First, it enabled Kepler to discover the three laws governing the motion of the planets. Second, it enabled a proof to be given of Newton’s gravitational force of attraction (binding all objects together). Neither of these advances would have been possible on the pre-Copernican model.
How, though, does Kant propose to establish his Copernican revolution? It can be established, he thinks, in ways analogous to those that established Copernicus’s own hypothesis. First, on Kant’s revolutionary model of the relationship between our experience and its objects, he believes that we can explain how mathematics and natural science have provided us with universal and necessary knowledge of these objects. Second, he believes that it will enable us to provide proofs of the principles lying at the basis of natural science. Neither of these achievements is possible on the traditional model. Accordingly, just as Copernicus’s own hypothesis was established because it, and it alone, enabled us to discover the laws of planetary motion and, at the same time, to provide a proof of Newton’s force of attraction, so Kant’s Copernican revolution is to be established because it, and it alone, can explain how we are in possession of universal and necessary objective principles in mathematics and natural science, and at the same time provide proofs of the first principles of natural science. The theory that Kant constructs, on the basis of his Copernican revolution, he calls ‘transcendental idealism’.
In fact, as he sees it, there is a further ground for accepting his Copernican revolution. He argues that, on the traditional conception of the relationship between the mind and its hoped-for objects, we are bound to involve ourselves in inextricable contradictions when we attempt to prove certain judgments which entirely transcend experience (for instance, a judgment concerning freedom of the will); whereas, on his opposing, Copernican-style conception, we can show that no such contradictions arise. Now a theory can only be justified if it does not lead to contradiction. Accordingly (on the assumption that there really are only these two theories), Kant regards the consistency of his own, revolutionary theory, compared with the unavoidable inconsistencies of the traditional theory, as a further proof of the correctness of his Copernican project, and hence of transcendental idealism. Moreover (as emerges in the later Critique of Practical Reason and Critique of Judgment), there are, on the alternative theory, further contradictions in our thought – our thought about morality and beauty – which, he will argue, can be resolved only by embracing his revolution.
Hume’s scepticism about causation and Kant’s Copernican revolution
In order to illustrate how the Kantian Copernican revolution bears on central issues in philosophy, let us return to Hume’s scepticism about causation. Hume – at least as Kant reads him – sees nothing inconceivable in the behaviour of objects in the spatio-temporal world always having been, or suddenly becoming, totally chaotic. Since a state of lawlessness in nature implies no contradiction, it is by Hume’s lights entirely conceivable. Moreover, although chaos in nature would obviously preclude us from connecting together objects, or their states, according to universal or necessary laws, Hume allows – again as Kant reads him – that we should still be able to experience objects and their changing states.
Now although this scepticism is diametrically opposed to the position that Kant adopts as a result of his Copernican revolution, there is a sense in which he accepts it. He accepts that if the traditional picture of the relationship between objects in the spatio-temporal world and ourselves is correct, then Hume’s story of a nature in chaos cannot be dismissed. But now consider Kant’s alternative, revolutionary picture. In particular, consider his claim that the laws by which the objects of nature can alone be experienced derive from certain fundamental concepts in us. If one of these fundamental concepts is the concept of cause, and the corresponding law is the causal principle (viz. every change of state must have a cause), then it would follow that we can only experience a change of state in so far as it is subject to causal law. Remarkable though such a conclusion would be if it could be shown, it can hardly be said fully to meet Hume’s scepticism. Even granting that we cannot experience a nature which is non-causal in respect of any change of state, that would seem to put constraints only on our ability to perceive such a spatio-temporal world. But Hume’s scepticism chiefly concerns the conceivability of a non-causal nature, not our capacity or incapacity to experience it.At this point, we need to bring in the other part of the Kantian Copernican revolution: that space and time are merely properties of our mind, and hence, that everything appearing therein must in reality be mind-dependent. If the objects of our senses (the objects in space and time) are, in reality, mind-dependent, then any condition on our being conscious of, and so of our experiencing, these objects must equally be a condition on the possible objects of our experience. For example, if we cannot think, and so experience, a change in the objects of our senses, except under the condition that the data apprehended by us be subject to the law of causality, then it follows – given the mind-dependency of this data – that there can be no acausal change in spatio-temporal objects. If everything that can appear in space and/or time is mind-dependent, then any restriction on our ability to experience spatio-temporal objects must equally be a restriction on the possible objects that can exist in space and time.
In sum, Kant accuses Hume of putting the cart before the horse. As Kant sees it, Hume assumes that spatio-temporal objects exist independently of our possible experience. On this traditional picture, it has to be admitted that we cannot see why these objects must conform to any of the concepts that may exist in us for connecting together the given sensuous data under laws. In particular, therefore, it is impossible to see why spatio-temporal objects must, in respect of their
