Kant

The form- is given by the intellect, independent of all experience, a priori, and signifies the function, manner and law of knowing and acting, which the subject finds in itself prior to all experience.

The matter- is the subjective sensations which we receive from the external world.

Through these two elements the benefits of Rationalism and Empiricism are united in the same judgment: the form represents the universal and necessary element, while the matter represents the empirical data. The judgment thus resulting (synthetic a priori) is universal and necessary in virtue of the form, and valid for the empirical world in virtue of the matter. It is to be noted that for the formation of a synthetic a priori judgment it is necessary to have both elements: Form without matter is empty and void; matter without form is blind.

Clearly, a knowledge obtained through Kant's synthetic a priori judgments is of phenomenal value only; it does not give a valid understanding of the objects "in se" or as they exist in nature (noumena), but only in so far as they are thought by the subject. Kant's thinking ego does not assimilate the object, as traditional philosophy maintains, but constructs it. In fact, both matter and form (sensations) are subjective elements and do not bespeak reality; this remains ever separate and distinct from the subject

1. Transcendental Aesthetic

The beginning of knowledge is in sensibility, in the reception of sensations. In order to constitute knowledge, sensations must be located in space, if they come to us through the external senses; and in time, i.e., succeeding one another, no matter what their origin -- even if they be simple states of consciousness, such as pleasure and pain.

Now, for Kant, space and time are not realities existing in themselves, as Newton believed, nor are they realities coming from experience, as Aristotle maintained. They are, instead, a priori forms, that is, exigencies of our knowledge. Sense knowledge (pure intuition) carries within itself the following exigencies; Every sensation must be located in space, i.e., above or beneath, to the right or to the left, and in time, that is, antecedent, subsequent, or concomitant to other sensations. Hence space and time are conditions, not of the existence of things but of the possibility of their being manifested in us. In a word, they are subjective