Andrew Brook has recently tried to assimilate Kant’s project in the Critique of Pure Reason into the current model of cognitive science. Basically, he claims that Kant was quite ahead of his time in that he regarded the common philosophical issues of his time as dead-ends. “Like contemporary cognitive science but radically unlike other philosophies of his own time, Kant was blithely unconcerned about the great questions about knowledge of the external world, skepticism, solipsism etc.” Instead, Kant is reported to have proceeded with assumptions more closely related to those of cognitive science. “Unlike the [philosophical] tradition but like contemporary cognitive science, he simply took it for granted that we have knowledge: a priori knowledge about conceptual structures and perceptual knowledge of the world of space and time.” (Andrew Brook. “Kant and Cognitive Science”. In The Prehistory of Cognitive Science. Basingstoke, UK: Palgrave Macmillan, 2007: pp. 117-36) Actually, Kant wanted to prove the existence and justification of “a priori knowledge about conceptual structures” (the categories). In doing so, he sought to prove his own answers to the “great questions about knowledge” in a doctrine which he called transcendental idealism.
Transcendental idealism is founded upon Kant’s distinction between things as they appear to us and things as they are in themselves. He makes this distinction in the preface as part of his Copernican revolution which is the experimental hypothesis that things conform to our methods of representation. Things as they appear to us are things that conform to our ways of representation. To consider a thing in itself is to consider it such that our representations would have to conform to it. Thus, transcendental idealism holds that we cannot be certain about anything concerning things in themselves because we cannot be sure that our representations have really conformed to the thing. All we can really know is that which can or does appear to us in experience. And we can know about our way of representing by considering that which is presupposed in any experience we may have. In this way, Kant discovers that space and time are necessary for anything appearing to us at all. Kant argues for our knowledge of spacio-temporal structures rather than taking them for granted as Brook claims.
Kant distinguishes transcendental idealism from other kinds of idealism. Specifically, he denies problematic idealism and dogmatic idealism. Problematic idealism is the problem raised by Descartes concerning the existence of an external world. Kant argues against this by proving that “ever our inner experience, which for Descartes is indubitable, is possible only on the assumption of outer experience” (B275). Problematic idealism, attributed to Berkeley, is the doctrine that there is no matter at all in the world and that all of our experiences are illusions, or ideas existing merely in our minds and the mind of God. This view is closer to transcendental idealism, but Kant explicitly denies it. Appearances are not illusions according to Kant because, objects are “always regarded as something given” (B69), which means that they have their source outside us. In order to deny each of these other kinds of idealism, Kant shows that there must be some objective reality independent of us. So, contrary to Brook’s claims quoted earlier, Kant was quite concerned with skepticism, the external world, and other questions about knowledge of reality in general.
From transcendental idealism, it follows that there must be a priori concepts that we use in experience. As the Copernican hypothesis implies, these concepts are that to which objects must conform it order for us to have knowledge of them. An empiricist like Hume would agree that we have concepts that must be used in experience, but he or she would not know what to say about their origin other than to say they are phantoms of the brain or something like that. Kant on the other hand will say that these concepts must be a priori and precede experience since they are the conditions of having any experience at all. Kant takes the forms of judgements as his clue to discovering what these pure concepts might be. In judgements we apply a concept to a term so the basic ways in which we do that should bear some relation to the concepts we apply to objects in experience. Due to the several similarities between judging and cognizing, Kant concludes that there must be a concept of the understanding for each way in which we judge things in the world. This set of concepts is then called the categories, since Aristotle’s list of forms of judgement from which they were derived was also called that. If the account of the categories stopped here, then Brook’s claim that Kant takes them for granted might have been arguable. Just showing that we have a set of concepts that we use in cognizing objects, even if they are indispensable in that activity does not show that we are justified in using them or that we cannot have any experience at all without using them. And, Kant wants to make both of these claims.
One of the most important sections in the first Critique, and the section Kant said required the most labor, is the transcendental deduction. Kant has produced the categories which are the “subjective conditions of thought” for us. The transcendental deduction is meant to justify our usage of the categories, meaning showing how the categories are objectively valid. In contrast, Hume would agree that concepts such as causality are indispensable in our understanding of experience, but he denied that the kind of justification Kant seeks to provide in the transcendental deduction is possible. Kant thinks that there are some concepts, such as fate, commonly used in experience that are not justified. Thus, Kant wants to distinguish the categories from these folk concepts. Kant’s outlines his main strategy in the deduction: “If we can prove that by their means alone an object can be thought, this will be a sufficient deduction of them, and will justify their objective validity” (A96-7). Kant then goes on to argue that an object of experience must be subject to the categories if it is to be a unified experience at all. Regardless of Kant’s method of argument or even whether the argument succeeds, Kant was far from taking a priori knowledge about our conceptual structures for granted. Kant sought to show the origin and justification of this knowledge.
It seems that Brooks wants to say that Kant was only concerned with the contents and workings of our minds. But really he wanted to say quite a bit beyond that. He did want to discover the concepts we must use in any thought at all, but he did this only in order to say something about the world that we think about as well. In fact, in order to really justify the knowledge we have through the categories, Kant has to say that reality as it appears to us is also structured according to the categories. Thus we see how closely related these two parts of Kant’s project in the Critique of Pure Reason are. According to the transcendental deduction, objects can only become objects for us insofar as they conform to the conceptual structures with which we cognize objects. This claim would be quite meaningless if he had failed to prove–—or worse, if he had failed to address—the existence of objects independent of the way we think of them. Kant in fact argues for our “a priori knowledge about conceptual structures” and does so in close conjunction with his attempt to answer the “great questions about knowledge of the external world, skepticism, solipsism etc.”