priori_, though not as completed representations. They are
functions, necessary actions of the soul, for the execution of which a
stimulus from without, through sensations, is necessary, but which, when
once this is given, the soul brings forth spontaneously. The external
impulse merely gives the soul the occasion for such productive acts, while
their grounds and laws are found in its own nature. In this sense Kant
terms them "originally acquired," and in the Introduction to the _Critique
of Pure Reason_ declares that although it is indubitable that "all our
knowledge begins _with_ experience (impressions of sense), yet it does not
all arise _from_ experience." That a representation or cognition is _a
priori_[1] does not mean that it precedes experience in time, but that
(apart from the merely exciting, non-productive stimulation through
impressions already mentioned) it is independent of all experience, that it
is not derived or borrowed from experience.

[Footnote 1: The terms _a priori_ representation and pure representation
(concept, intuition) are equivalent; but in judgments, on the other hand,
there is a distinction. A judgment is _a priori_ when the connection takes
place independently of experience, no matter whether the concepts connected
are _a priori_ or not. If the former is the case the _a priori_ judgment is
pure (mixed with nothing empirical); if the latter, it is mixed.]

The material of intuition and thought is given to the soul, received by
it; it arises through the action of objects upon the senses, and is always
empirical. Intuition is the only organ of reality; in sensation the
presence of a real object as the cause of the sensation is directly
revealed. When Kant's transcendental idealism was placed by a reviewer on a
level with the empirical idealism of Berkeley, which denies the existence
of the external world, he distinctly asserted that it had never entered
his mind to question the reality of external things. Further, after the
existence of real things affecting the senses had been transformed in
his mind from a basis of the investigation into an object of inquiry,
he endeavored to defend this assumption (which at first he had naively
borrowed from the realism of pre-scientific thought) by arguments, but
without any satisfactory result.[1]

[Footnote 1: The task of confirming the existence of things in themselves
changes under his hands into another, that of proving the existence of
external