Kant's "Critique of Practical Reason" ("Kritik der praktischen
Vernunft"), published in 1788, is one of the most striking
disquisitions in the whole range of German metaphysical literature.
One of its paragraphs has alone sufficed to render it famous. The
passage concerning the starry heavens and the moral law as the two
transcendently overwhelming phenomena of the universe is, perhaps,
more frequently quoted than any other written by a German author.
This is the treatise which forms the central focus of Kant's
thinking. It stands midway between the "Critique of Pure Reason"
and the "Critique of Judgment." Herein Kant takes up the position
of a vindicator of the truth of Christianity, approaching his proof
of its validity and authority by first establishing positive
affirmations of the immortality of the soul and the existence of
God. It also includes a theory of happiness, and an argument
concerning the _summum bonum_ of life, the special aim being to
demonstrate that man should not simply seek to be happy, but
should, by absolute obedience to the moral law, seek to become
worthy of that happiness which God can bestow.
_I.--Analytic of Practical Reason_
Practical principles are propositions containing a general determination
of the will. They are maxims, or subjective propositions, when
expressing the will of an individual; objective, when they are valid
expressions of the will of rational beings generally.
Practical principles which pre-suppose an object of desire are
empirical, or experimental, and supply no practical laws. Reason, in the
scope of a practical law, influences the will not by the medium of
pleasure or pain. All rational beings necessarily wish for happiness,
but they are not all agreed either as to the means to attain it, or as
to the objects of their enjoyment of it. Thus, subjective practical
principles can only be reckoned as maxims, never as law.
A rational being ought not to conceive that his individual maxims are
calculated to constitute universal laws, and to become the basis of
universal legislation. To discover any law which would bring all men
into harmony is absolutely impossible.
One of the problems of practical reason is to find the law which can
necessarily determine the will, assuming that the will is free. The
solution of this problem is to be found in action according to the moral
law. We should so act that the maxim of our will can always be valid as
a principle of universal legislation. Experience shows how the moral
consciousness determines freedom of the will.
Suppose that someone affirms of his inclination for sensual pleasure
that he cannot possibly resist temptation to indulgence. If a gallows
were erected at the place where he is tempted, on which he should be
hanged immediately after satiating his passions, would he not be able to
control his inclination? We need not long doubt what would be his
answer.
But ask him, if his sovereign commanded him to bear false witness
against an honourable man, under penalty of death, whether he would hold
it possible to conquer his love of life. He might not venture to say
what he would choose, but he would certainly admit that it is possible
to make choice. Thus, he judges that he can choose to do a thing because
he is conscious of moral obligation, and he thus recognises for himself
a freedom of will of which, but for the moral law, he would never have
been conscious.
We obtain the exact opposite of the principle of morality if we adopt
the principle of personal private happiness as the determining motive of
the will. This contradiction is not only logical, but also practical.
For morality would be totally destroyed were not the voice of reason as
clear and penetrating in relation to the will, even to the most ordinary
men.
If one of your friends, after bearing false witness against you,
attempted to justify his base conduct by enumerating the advantages
which he had thus secured for himself and the happiness he had gained,
and by declaring that thus he performed a true human duty, you would
either laugh him to scorn or turn from him in horror. And yet, if a man
acts for his own selfish ends, you have not the slightest objection to
such behaviour.