is only a
practical rule, and never a moral law. A purely rational moral
philosophy, or Metaphysic of Morals, will serve the double end of
meeting a speculative requirement, and of furnishing the only true norm
of practice. It investigates the idea and principles of a potentially
pure Will, instead of the acts and conditions of human volition as
known from psychology. Not a complete Metaphysic of Morals, however,
(which would be a Critique of the pure Practical Reason), but merely a
foundation for such will be given. The supreme principle of morality is
to be established, apart from detailed application. First, common
notions will be analyzed in order to get at this highest principle; and
then, when the principle has been sought out, they will be returned
upon by way of synthesis.

In the first of the three main sections of the work, he makes the
passage from Common Rational Knowledge of Morals to Philosophical.
Nothing in the world, he begins, can without qualification be called
good, except _Will_. Qualities of temperament, like courage, &c., gifts
of fortune, like wealth and power, are good only with reference to a
good will. As to a good will, when it is really such, the circumstance
that it can, or cannot, be executed does not matter; its value is
independent of the utility or fruitlessness of it.

This idea of the absolute worth of mere Will, though it is allowed even
by the vulgar understanding, he seeks to establish beyond dispute, by
an argument from the natural _subjection_ of Will to Reason. In a being
well-organized, if Conservation or Happiness were the grand aim, such
subjection would be a great mistake. When Instinct could do the work
far better and more surely, Reason should have been deprived of all
practical function. Discontent, in fact, rather than happiness comes of
pursuit of mere enjoyment by rational calculation; and to make light of
the part contributed by Reason to happiness, is really to make out that
it exists for a nobler purpose. But now, since Reason _is_ a practical
faculty and governs the will, its function can only be to produce a
Will good in itself. Such a Will, if not the only good, is certainly
the highest; and happiness, unattainable by Reason as a primary aim,
and subject in this life altogether to much limitation, is to be sought
only in the contentment that arises from the attainment by Reason of
its true aim, at the sacrifice often of many a natural inclination.

He proceed