priori must be completely pure. Hence, although the highest principles
and fundamental conceptions of morality are certainly cognitions a
priori, yet they do not belong to transcendental philosophy;
because, though they certainly do not lay the conceptions of pain,
pleasure, desires, inclinations, etc. (which are all of empirical
origin), at the foundation of its precepts, yet still into the
conception of duty--as an obstacle to be overcome, or as an incitement
which should not be made into a motive--these empirical conceptions
must necessarily enter, in the construction of a system of pure
morality. Transcendental philosophy is consequently a philosophy of
the pure and merely speculative reason. For all that is practical,
so far as it contains motives, relates to feelings, and these belong
to empirical sources of cognition.

If we wish to divide this science from the universal point of view
of a science in general, it ought to comprehend, first, a Doctrine
of the Elements, and, secondly, a Doctrine of the Method of pure
reason. Each of these main divisions will have its subdivisions, the
separate reasons for which we cannot here particularize. Only so
much seems necessary, by way of introduction of premonition, that
there are two sources of human knowledge (which probably spring from
a common, but to us unknown root), namely, sense and understanding.
By the former, objects are given to us; by the latter, thought. So
far as the faculty of sense may contain representations a priori, which
form the conditions under which objects are given, in so far it
belongs to transcendental philosophy. 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.