ion, but it is not the limit of our
understanding, since it stimulates our faculty of reason, but does not
satisfy its desire for knowledge. While all our knowledge may begin with
sensible impressions or experience, there is an element in it which does
not rise from this source, but transcends it. That knowledge is
transcendental which is occupied not so much with mere outward objects
as with our manner of knowing those objects, that is to say, with our _a
priori_ concepts of them. All our knowledge is either _a priori_ or _a
posteriori_. That is _a posteriori_ knowledge which is derived from
sensible experience as including sensible impressions or states; while
_a priori_ knowledge is that which is not thus gained, but consists of
whatever is universal or necessary. A complete "Transcendental
Philosophy" would be a systematic exposition of all that is _a priori_
in human knowledge, or of "all the principles of pure reason." But a
"Critique of Pure Reason" cannot include all this. It can do little more
than deal with the synthetic element or quality in _a priori_ knowledge,
as distinguished from the analytic element.

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 aesthetic 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 sou