Propositions, according to Kant, 1787, can also be divided into two other types: empirical and a priori; empirical propositions depend entirely on sense perception, but a priori propositions have a fundamental validity and are not based on such perception.
Kant's claims that it is possible to make synthetic a priori judgments and regards that the objects of the material world is fundamentally unknowable; therefore, from the point of view of reason, they serve merely as the raw material from which sensations are formed.
Kant maintains that the category has no other application in knowledge than to objects of experience.
To think an object and to know an object are different things.
Accordingly, knowledge involves two factors: the concept and the intuition.
For the only intuition possible to us is sensible, the thought of an object can become knowledge only in so far as the concept is related to objects of the senses.
This determines the limits of the pure concepts of understanding.
Kant insists that since there lies in us a certain form of a priori sensible intuition, the understanding, as spontaneity, is able to determine inner sense through the manifold of given representations in accordance with the synthetic unity of apperception.
In this way the categories obtain objective validity.
Further Kant insists that figurative synthesis is the synthesis of the manifold which is possible and necessary a priori.
It opposes to combination through the understanding which is thought in the mere category in respect to intuition in general.
It may be called the transcendental synthesis of imagination that is the faculty of representing in intuition of an object which is not present; and of course it belongs to sensibility.
For the principle that all intuition are extensive, as it was elaborated in the Critique of Pure Reason, Kant, 1787, proves that all appearances are extensive magnitudes and consciousness of the synthetic unity of the manifold is the concept of magnitude.
A magnitude is extensive when the representation of the parts makes possible and therefore necessarily precedes the representation of the whole.
In appearances, the real i.e. an object of sensation, has intensive magnitude or a degree.
Kant proves that perception is empirical consciousness and appearances are not pure intuition like time and space.
They contain the real of sensation as subjective representation.
Therefore, from empirical consciousness to pure consciousness a graduated transition is possible.
There is also possible a synthesis in the process of generating the magnitude of a sensation as well as that the sensation is not itself an objective representation.
Since neither the intuition of space nor time has met with it, its magnitude in not extensive but intensive.
Kant proves that experience is possible only through the representation of a necessary connection of perceptions.
For experience is an empirical knowledge, it is a synthesis of perceptions; it is not contained in perception but containing itself in one consciousness of the synthetic unity of the manifold of perceptions.
And since time itself cannot be perceived, the determination of the existence of objects in time can take place only through their relation in time in general.
Since this determination always carry a necessity with time, experience is only possible through a representation of necessary connection of perceptions.
Kant ascertains that the three modes of time are duration, succession, and coexistence and the general principles of the three analogies rest on the necessary unity of apperception at every instant of time.
These general principles are not concerned with appearances but only with existence and relation in respect to existence.
Existence, therefore, can never be known as a priori and can not be constructed like mathematical principles so that these principles will be only regulative.
These analogies are valid for empirical employment of understanding but not for transcendental one.
In the principle, we use the category; but in its application to appearances, we use the schema.
Kant, I., 1787, “The Critique of Pure Reason: Preface To The Second Edition”, Translated By J. M. D. Meiklejohn, Retrieved 2003