Any empirical researcher, any natural scientist, takes as his field of investigation some aspect or selection of natural objects and events, located in space and occurring or persisting in time. Among these natural objects, of particular concern to biologists, psychologists, and physiologists, are our human selves. The scientist's business is to discover the laws of working which govern the behaviour and account for the characteristics of his selected objects. But those general features that constitute the very framework of such enquiries — the spatio-temporality of nature and the existence of discoverable law — are alike attributed by Kant to the constitution of the human mind, whence he contentedly draws the conclusion that empirical enquiry can yield us knowledge only of appearances — of the appearances that things present to beings constituted as we are. Of things as they are in themselves (including ourselves as we are in ourselves) experience and scientific investigation can yield no knowledge at all. The field of empirical enquiry is nature: but all the characteristics of natural things (including ourselves as natural objects) are thoroughly conditioned by features which have their source in the human subject.
Kant distinguishes two primary subjective sources of these features: the sensibility and the understanding. Sensibility is passive or receptive: it is the mind's capacity so to be affected by things as they are in themselves that mental contents or representations which Kant calls 'intuitions' or 'perceptions' are thereby generated. Within this receptive faculty of sensibility Kant distinguishes between 'inner' and 'outer' sense, saying that time is nothing but the form of the one and space nothing but the form of the other. The doctrine is that the temporal character of experience in general, and of its objects, and the possession by some intuitions of the character of spatiality which allows of their being so ordered as to count as perceptions of objects in space are due to the constitution of inner and outer sense respectively; and that, in particular, time, the form of inner sense, is the mode of ordering which results from the self-affection of ourselves as we are in ourselves. For, in addition to the passive or merely receptive faculty of sensibility, we have the active, affecting faculty of understanding. Understanding is the faculty which, acting on the sensibility, enables us to conceptualize our intuitions, and, more, it is the subjective source of those general principles of conceptualization (the categories) which enable and require us so to conceptualize our intuitions as to give them the character of perceptions of a law-governed world of objects of which the governing laws are open to investigation by the methods of empirical science.
For this theory, as elaborated in the Critique of Pure Reason, Kant made great claims. He claimed that it provided the unique explanation of certain features of our empirical knowledge of nature (i.e. of the world of appearances), features which were necessary conditions of the very possibility of any such knowledge; that it supplied a salutary demonstration of the impossibility of theoretical knowledge of the supersensible realm of things as they are in themselves; and that, at the same time, it left room, not for theoretical knowledge, but for the morally based conviction that the requirements of moral responsibility and moral justice were somehow fulfilled in that realm inaccessible to our knowledge.
These claims we need not consider here. From the brief sketch given above, it seems hardly to be expected that Kant's transcendental theory of mind should have much in common with the firmly empirical theories current among psychologists and physiologists who concern themselves with the mind as a naturally given phenomenon, or, indeed, with the views of those philosophers of mind who concern themselves with the analysis or elucidation of the mental concepts which men and women employ in thinking about themselves and their fellows. When Kant speaks of the 'human mind' or of 'ourselves' as the subjective source of time, space, and the categories, it seems that it must be of those mysteries, ourselves as we are in ourselves, that he is speaking and not of ourselves as we know ourselves; and when he distinguishes sensibility and understanding, we cannot take him as referring to such familiar objects of empirical study as sensory receptors and the day-to-day workings of human intelligence.
Kant distinguishes further faculties: notably that of imagination, which serves sense and understanding as their indispensable go-between, synthesizing the manifold and discrete data of sense in such a way as to make possible recognition of objects as falling under empirical concepts. In this doctrine of synthesis we may be tempted to find a near or remote analogue of some findings of empirical (including physiological) psychology. But the qualification 'transcendental' standing before the phrase 'synthesis of imagination' should warn us to tread warily. The transcendental synthesis of imagination is not to be conceived as any kind of occurrent process which could be empirically studied. The doctrine is more intelligibly seen as reflecting an inescapable feature of sense perception of a world of objects: the fact that we cannot, in general, veridically characterize even a momentary perception except by acknowledging that, for example, we see what we see as a dog, say, or as a tree — thus uniting, as it were, the instantaneous impression with other past or possible impressions (of the same object or of different objects of the same kind) which would similarly require, for their characterization, employment of the same general concept. This infusion or penetration of momentary sense impressions by object concepts which extend beyond (and 'combine') them, Kant saw as a necessary condition of experience of a world of objects; and thus he saw imagination as a necessary ('transcendental') mediator between sense, as merely receptive, and understanding as the faculty of concepts in general and in particular as the source of those very general a priori concepts (the categories) which necessarily found a footing in experience in the use we make of our merely empirical concepts of types of object and event. (There are instructive parallels and contrasts to be drawn between Kant's doctrine of imagination and that of Hume.)
To the faculty of 'reason' Kant assigns a role which includes, but goes beyond, those merely conceptualizing, judging, and generalizing operations of the understanding whereby empirical knowledge of nature is gained and extended. Reason typically demands more than this limited knowledge which always leaves room for further questions and thus is knowledge, as Kant puts it, only of the 'conditioned', for reason sets before itself the ideal of ultimate explanations, of final and complete knowledge which would leave no room for further questions. Insofar as this 'demand of reason for the unconditioned' encourages us to push our empirical researches in the direction of more and more comprehensive theories or into ever-remoter regions of the physical universe or of past time, its effect is wholly beneficial. But insofar as we are encouraged to believe that the demand can be met, that we can, by pure reasoning, attain knowledge of objects answering to reason's 'ideas' of the unconditioned, its effect is simply to generate illusion, for our knowledge is necessarily confined to the realm of experience, the realm of appearances, in which no such objects are to be found.
Rather less convincingly, Kant finds for pure reason a 'practical' role as the essential source and end of morality. He further suggests that, though we are denied theoretical knowledge of the supersensible realm of things as they are in themselves, yet reason in its practical role may yield moral certainties, falling short of knowledge, regarding that realm. He argues that our recognition of the unconditional binding force of the moral law carries with it both a belief in freedom of the will — a power of free choice which we do not possess as natural beings subject to causal determination but may possess as we supersensibly are in ourselves — and a belief in the supersensible fulfilment of the demands of moral justice and hence in a supersensible divinity capable of securing the moral ideal.
A question naturally arises regarding the internal consistency of the 'critical' philosophy and in particular of the doctrines of 'transcendental idealism'. If the spatio-temporality and law-likeness of nature and all that is in it are to be attributed to a subjective source in the human mind, this source cannot be identified with the human mind as a part of nature, the topic of empirical psychology — a discipline that Kant rather dismissively describes as a kind of 'physiology of inner sense'. So when Kant speaks of our sensibility and our understanding as the source of space, time, and the categories, it must be to ourselves as we (supersensibly) are in ourselves that he is referring. But this conclusion appears to be in direct contradiction to the doctrine that nothing can be known of things (including ourselves) as they are in themselves: a doctrine he is at pains to emphasize in his criticism of 'rational psychology' which seeks to argue from the bare fact of self-consciousness to the conclusion that the soul is a simple, immaterial, indestructible substance. The fallacies of 'rational psychology' Kant declares to be among those to which pure reason is prone in its search for the unconditioned which cannot be found in experience. It is not clear why Kant's own brand of what might be called 'transcendental psychology' — which is clearly distinguished from the empirical — does not fall under the same interdict that he places on 'rational psychology'.
These (and other) difficulties may tempt us to reconstrue, or reconstruct, the central doctrines of the critical philosophy, by (i) eliminating all reference to ourselves other than those natural selves which can be empirically studied and (ii) interpreting Kant's doctrine of the mind as concerned with certain powers and properties which we ordinary human beings (objects in nature) innately possess, and our possession of which is a necessary condition of our enjoyment of the type of experience that we do enjoy and of attainment of such knowledge of nature, including our own nature, as we do attain. Such a radically reinterpreted, such a domesticated, Kant would perhaps be more intellectually acceptable to us, but he would not be the great and difficult philosopher that he is in himself.
A final note may be added concerning Kant's treatment of aesthetics in The Critique of Judgement, where he turns his philosophy of mind to strikingly good account. The judgement of taste, the judgement that an object of art or nature is beautiful, is subjective insofar as it necessarily involves, and rests on, a subjective feeling of pleasure; and yet it claims universal or objective validity. This claim Kant declares justified insofar as the feeling of pleasure results from the fact that the formal properties of the object are such as to excite the harmonious free play of the faculties of understanding and imagination, for these faculties are common to all men. The functioning of these faculties in this connection is described as 'free play' just because it is not under the governance of concepts such as we employ in ordinary non-aesthetic empirical judgements; i.e. our aesthetic response is not to the object as being of some general kind, but rather to it as the unique individual that it is.
(Published 1987)
— Sir Peter Strawson
