The philosophy of Immanuel Kant

THIS epoch-making work was first published in 1781. It forms the first of a remarkable trilogy, its companion studies being The Critique of Practical Reason, 1788; and The Critique of the Power of Judgement, 1790. In Kant's view Pure Reason teaches that human knowledge is based on experience; but Practical Reason recognizes that there are a priori in the mind certain notions independent of experience and postulating the ideas of human liberty, God and immortality. Thus, while distinguishing the provinces of materialism and idealism, he attempted to find a bond of union between them.


EXPERIENCE is something of which we are conscious. It is the first result of our comprehension, but it is not the limit of our understanding, since it stimulates our faculty of reason, but does not satisfy its desire for knowledge.

While all our knowledge may begin with sensible impressions or experience there is an element in it which does not rise from this source, but transcends it. That knowledge is transcendental which is occupied not so much with mere outward objects as with our manner of knowing those objects, that is to say, with a priori concepts of them.

All our knowledge is either a priori or a posteriori. That is a posteriori knowledge which is derived from sensible experience as including sensible impressions or states; while a priori knowledge is that which is not thus gained, but consists of whatever is universal or necessary.

A complete Transcendental Philosophy would be a systematic exposition of all that is a priori in human knowledge, or of 'all the principles of pure reason.' But a Critique of Pure Reason cannot include all this. It can do little more than deal with the synthetic element or quality in a priori knowledge, as distinguished from the analytic elements.

We perceive objects through our sensibility which furnishes us, as our faculty of receptivity, with those intuitions that become translated into thought by means of the understanding. This is the origin of our conceptions, or ideas. I denominate as matter that which in a phenomenon corresponds to sensation; while I call form that quality of matter which presents it in a perceived order. Only matter is presented to our minds a posteriori; as to form, this must inevitably exist in the mind a priori, and therefore it can be considered apart from all sensation.

Pure representation, entirely apart from sensation, in a transcendental signification, forms the pure intuition of the mind, existing in it as a mere form of sensibility. 'Transcendental aesthetic' is the science of all the principles of sensibility. But transcendental logic is the science of the principles of pure thought. In studying the former we shall find that there are two pure forms of sensuous intuition, namely, space and time.

Are space and time actual entities? Or are they only relations of things? Space is simply the form of all the phenomena of external senses; that is, it is the subjective condition of the sensibility under which alone external intuition is possible. Thus the form of all phenomena may exist a priori in the soul as a pure intuition previous to all experience. So we can only speak of space and of extended objects from the standpoint of human reason. But when we have abstracted all the forms perceived by our sensibility, there remains a pure intuition which we call space. Therefore our discussion teaches us the objective validity of space with regard to all that can appear before us externally as an object; but equally the subjective ideality of space with regard to things if they are considered in themselves by our reason, that is, without taking into account the nature of our sensibility.

Time is not empirically conceived of; that is, it is not experimentally apprehended. Time is a necessary representation on which all intuitions are dependent, and the representation of time to the mind is thus given a priori. In it alone can phenomena be apprehended. These may vanish, but time cannot be put aside.

Time is not something existing by itself independently, but is the formal condition a priori of all phenomena. If we deduct our own peculiar sensibility, then the idea of time disappears indeed, because it is not inherent in any object, but only in the subject which perceives that object. Space and time are essential a priori ideas, and they are the necessary conditions of all particular perceptions. From the latter and their objects we can, in imagination without exception, abstract; from the former we cannot.

Space and time are therefore to be regarded as the necessary a priori pre-conditions of the possibility and reality of all phenomena. It is clear that 'transcendental aesthetic' can obtain only these two elements, space and time, because all other concepts belong to the senses and pre-suppose experience, and so imply something empirical. For example, the concept of motion pre-supposes something moving, but in space regarded alone there is nothing that moves; therefore, whatever moves must be recognized by experience, and is a purely empirical datum.

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