not know—a warning to those who call themselves independent thinkers and who give
the name of speculator to those who apply themselves exclusively to the rational part of
philosophy. This warning would be that they should not, at one and the same time, carry
on two employments which differ widely in the treatment they require, and for each of
which perhaps a special talent is required, since the combination of these talents in one
person produces only bunglers. I only ask whether the nature of the science does not
require that a careful separation of the empirical from the rational part be made, with a
metaphysics of nature put before real (empirical) physics and a metaphysics of morals
before practical anthropology. Each branch of metaphysics must be carefully purified of
everything empirical so that we can know how much pure reason can accomplish in
each case and from what sources it creates its a prioriteaching, whether the latter
inquiry be conducted by all moralists (whose name is legion) or only by some who feel
a calling to it.
Since my purpose here is directed to moral philosophy, I narrow my proposed
question to this: Is it not of the utmost necessity to construct a pure moral philosophy
which is completely freed from everything which may be only empirical and thus
belong to anthropology? That there must be such a philosophy is self-evident from the
common idea of duty and moral laws. Everyone must admit that a law, if it is to hold
morally (i.e., as a ground of obligation), must imply absolute necessity; he must admit
that the command: Thou shalt not lie, does not apply to men only as if other rational
beings had no need to observe it. The same is true for all other moral laws properly so
called. He must concede that the ground of obligation here must not be sought in the
nature of man or in the circumstances in which he is placed but a priorisolely in the
concepts of pure reason, and that every precept which rests on principles of mere expe-
rience, even a precept which is in certain respects universal, so far as it leans in the least
on empirical grounds (perhaps only in regard to the motive involved) may be called a
practical rule but never a moral law.
Thus not only are moral laws together with their principles essentially different
from all practical knowledge in which there is anything empirical, but all moral philos-
ophy rests solely on its pure part. Applied to man, it borrows nothing from knowledge
of him (anthropology) but gives man, as a rational being,a priorilaws. No doubt these
laws require a power of judgment sharpened by experience partly in order to decide in
which cases they apply and partly to procure for them access to man’s will and to pro-
vide an impetus to their practice. For man is affected by so many inclinations that,
though he is capable of the Idea of a practical pure reason, he is not so easily able to
make it concretely effective in the conduct of his life.
A metaphysics of morals is therefore indispensable, not merely because of
motives to speculation on the source of the a prioripractical principles which lie in our
reason, but also because morals themselves remain subject to all kinds of corruption so
long as the guide and supreme norm for their correct estimation is lacking. For it is not
sufficient to that which should be morally good that it conform to the law; it must be
done for the sake of the law. Otherwise its conformity is merely contingent and spurious
because, though the unmoral ground may indeed now and then produce lawful actions,
more often it brings forth unlawful ones. But the moral law can be found in its purity
and genuineness (which is the central concern in the practical) nowhere else than in a
pure philosophy; therefore metaphysics must lead the way, and without it there can be
no moral philosophy. Philosophy which mixes pure principles with empirical ones does
not deserve the name, for what distinguishes philosophy from common sense knowl-
edge is its treatment in separate sciences of what is confusedly apprehended in such852 IMMANUELKANT
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