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 changes, be subject to the law of causality. On the other hand, if Kant’s Copernican picture is correct, it would have the following consequences. First, we can have no experience of spatio-temporal objects changing their states except in so far as the apprehended manifold can be thought by us as subject to the law of causality. Second, all these changing objects are dependent for their existence on our capacity to think the given manifold by means of that law. Accordingly, not only must Hume have been wrong to suppose that we might be able to experience spatio-temporal objects changing randomly; more significantly, he must have been wrong to hold that there could exist any acausal changes in these objects.
Before turning to the second stage of Kant’s Copernican project, I must stress that in this introduction I am aiming only to provide an overview of some of the main themes of the First Critique.In particular, what I have attempted in the last few paragraphs is nothing more than an outline of the strategy by which Kant hopes to answer Hume. Clearly, it is one thing to outline a strategy and another thing to show how it can be filled in to provide a convincing reply to scepticism. Most conspicuously, there are two issues that need to be addressed. First, we need to understand why space and time are held to have a mind-dependent status. Second, we need to understand why our capacity to have any experience of objects requires that the data apprehended through the senses must be subject to laws that derive from concepts existing in our mind. Without a proper appreciation of Kant’s responses to these issues, there is simply insufficient detail to decide whether he has given a plausible, let alone a correct, response to Hume. In fact, both issues are discussed at length in the First Critique. Kant’s treatment of them forms the backbone of his Copernican project.
Metaphysics
So far, we have concentrated on the first stage of Kant’s Copernican revolution: the investigation of how the judgments in pure mathematics and natural science can exist (as they actually do). But we saw that he also maintains that metaphysics is essentially made up of judgments which have the same status as those in mathematics and natural science. With metaphysics, however, it is by no means clear that its central claims can be known to be true: the protracted and indecisive debates about every one of them strongly suggests that they cannot. In the section of the First Critique entitled ‘Transcendental Dialectic’, he turns to the second stage of his Copernican revolution: the investigation of whether the central claims of metaphysics can be substantiated. He concludes that our theoretical reason is unable to show any of them to be true or false.
His ground for reaching this conclusion is closely connected with the first stage of his Copernican project. For Kant’s explanation of how judgments in pure mathematics and natural science can hold with necessity and universality, while yet not being analytically true, is that they make our experience, our empirical knowledge of spatio-temporal objects, possible. (I have tried to illustrate this with the particular case of the law of causality: this law is held to make possible our experience of change of states among spatio-temporal objects.) But the central (positive) claims of metaphysics – that the soul is immortal, that we possess free will, and that God exists – have no relationship to sense experience. They entirely transcend it: they can neither be shown to make sense experience possible nor, given their status, be confirmed or disconfirmed through sense experience. Since, as he argues, these are the only ways by which theoretical reason can establish any non-analytic judgment, he concludes that we cannot prove or disprove the central claims of metaphysics by theoretical means.
It is vital, however, to appreciate that Kant does not maintain that the impossibility of verification – either directly by sense experience or indirectly by showing that they make sense experience possible – renders the central claims of metaphysics to be effectively unthinkable. He allows that we can consistently think a judgment like the soul is immortal, even though we cannot confirm or disconfirm it by theoretical means. Certainly, a judgment can only be established – or even given any determinate meaning – by showing that it has a relation, direct or indirect, to experience. But Kant denies that it is necessary for thinking any of the propositions of metaphysics in an indeterminate way that we should be able to relate them to sense experience.
In actual fact (though here we need to go outside the First Critique), he holds that the central claims of metaphysics can be established.And he holds that they can be established by showing that they make experience possible. But, with the central claims of metaphysics, the experience is not sense experience, but moral experience, our recognition of duty and of the need to pursue the highest good. This recognition, however, is made known to us not by theoretical but by practical reason.
One way of understanding Kant’s moral philosophy is to see it as attempting to prove the key judgments of metaphysics by showing that they make our moral experience possible. His idea is that we can only explain the existence of our moral experience – the demands of which we cannot doubt – by acknowledging the truth of the central claims of metaphysics (just as, in the First Critique,he argues that we can only explain the existence of mathematics and natural science – the reality of which we cannot doubt – by acknowledging that space and time are properties of our mind, and that the fundamental laws of nature derive from concepts in our understanding).We shall obviously need to consider Kant’s proof of these metaphysical claims when we examine his Copernican revolution in relation to morality.
Returning to the Copernican revolution as this is exemplified in the First Critique, Kant’s main negative point is that the traditional methods of the metaphysician must be given up.The central claims of metaphysics cannot be established by employing theoretical reason: they are not true solely in virtue of the meaning of the terms involved, and it is useless to seek to employ mathematics or any of the principles of natural science outside possible sense experience. Any attempt to establish the key judgments of metaphysics by employing mathematics or natural science is bound, Kant argues, to be dialectical (i.e. to be fallacious). Yet with respect to theoretical reason, it is only the employment of mathematics and natural science that can possibly yield informative judgments having the same status as the central claims of metaphysics. Accordingly, so far as our search for knowledge is concerned, the message of the First Critique is that this search is defensible where it is based on sense experience, or where it bears upon the possibility of