[*Footnote: As to the existence of pure natural science, or physics,
perhaps many may still express doubts. But we have only to look at
the different propositions which are commonly treated of at the
commencement of proper (empirical) physical science--those, for
example, relating to the permanence of the same quantity of matter,
the vis inertiae, the equality of action and reaction, etc.--to be
soon convinced that they form a science of pure physics (physica pura,
or rationalis), which well deserves to be separately exposed as a
special science, in its whole extent, whether that be great or
confined.]

Yet, in a certain sense, this kind of knowledge must
unquestionably be looked upon as given; in other words, metaphysics
must be considered as really existing, if not as a science,
nevertheless as a natural disposition of the human mind (metaphysica
naturalis). For human reason, without any instigations imputable to
the mere vanity of great knowledge, unceasingly progresses, urged on
by its own feeling of need, towards such questions as cannot be
answered by any empirical application of reason, or principles derived
therefrom; and so there has ever really existed in every man some
system of metaphysics. It will always exist, so soon as reason
awakes to the exercise of its power of speculation. And now the
question arises: "How is metaphysics, as a natural disposition,
possible?" In other words, how, from the nature of universal human
reason, do those questions arise which pure reason proposes to itself,
and which it is impelled by its own feeling of need to answer as
well as it can?

But as in all the attempts hitherto made to answer the questions
which reason is prompted by its very nature to propose to itself,