The Critique of Pure Reason

The transcendental doctrine of sense must form the first part of our science of elements, because the conditions under which alone the objects of human knowledge are given must precede those under which they are thought

By the former, objects are given to us; by the latter, thought.

hat there are two sources of human knowledge

Human reason, in one sphere of its cognition, is called upon to consider questions, which it cannot decline, as they are presented by its own nature, but which it cannot answer, as they transcend every faculty of the mind.

our knowledge may relate to objects, it is at least quite clear that the only manner in which it immediately relates to them is by means of an intuition

We find that reason perpetually comes to a stand, when it attempts to gain à priori the perception even of those laws which the most common experience confirms.

We find it compelled to retrace its steps in innumerable instances, and to abandon the path on which it had entered, because this does not lead to the desired result.

As regards clearness, the reader has a right to demand, in the first place, discursive or logical clearness, that is, on the basis of conceptions, and, secondly, intuitive or æsthetic clearness, by means of intuitions, that is, by examples or other modes of illustration in concreto.

As regards certitude, I have fully convinced myself that, in this sphere of thought, opinion is perfectly inadmissible, and that everything which bears the least semblance of an hypothesis must be excluded, as of no value in such discussions.

Pure reason is a perfect unity; and therefore, if the principle presented by it prove to be insufficient for the solution of even a single one of those questions to which the very nature of reason gives birth, we must reject it, as we could not be perfectly certain of its sufficiency in the case of the others.