3. Kant.
The most notable attempt to provide a new
basis for ascertaining
immortality of the soul, was
Kant's “moral” argument.
His starting point was that
man is not only a rational but also a moral
being, and
that human reason has two functions, one
“speculative”
or theoretical (“pure
reason”), and the other concerned
with moral action
(“practical reason”). In his Critique
of Pure Reason (1781; revised 1787), Kant showed
that
God, freedom, and immortality are ideas which specu-
lative reason can form but cannot prove. They are,
however, “postulates” of “practical
reason,” that is,
they “are not theoretical dogmas
but presuppositions
which necessarily have only practical import...
they
give objective reality to the ideas of practical reason
in
general.” Thus the immortality of the soul must be
true because
morality demands it. In his Critique of
Practical
Reason (1789), Kant argued that the highest
good (summum bonum) is the union of happiness and
virtue. But
while happiness can be attained in this life,
perfect virtue
(“holiness”) cannot and requires, there-
fore, that the existence of man be prolonged to
infinity.
Thus there must be another, future life. Later on, Kant
modified this argument somewhat by stating that we
are required
by moral law to become morally perfect.
But “no rational being
is capable of holiness at any
moment of his existence. Since, however, it
is required
as practically necessary, it can be found in a progress
which continues into infinity.... This infinite progress,
however, is
possible only if we assume an infinitely
lasting existence of the same
rational being (which is
called the immortality of the soul)”
(Critique of Practi-
cal
Reason, trans. L. W. Beck [1949], pp. 225-26).
Unfortunately, there is no absolute necessity that
reality will yield to
moral demands unless, of course,
we assume that the world is ruled, as Kant
asserts,
“with great wisdom” and with a purpose which
in-
cludes the moral perfection of man.
This, too, however,
can be “proved” only as a
postulate of practical reason.
No wonder, then, that Kant's moral argument
for
immortality of the soul failed to impress even his
admirers.
