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 æsthetic 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.