Kant thinks that religion must be understood thoroughly and rationally. We must work from within reason and the moral life. Kant develops an argument which would show that we’re immortal. It goes as follows.
We have the duty, which would become clear from a close examination of our lives, to perfect ourselves. Kant claims that one can only have the strong sense of duty, which any one of us would have if we concentrated on our inner moral life, if we were in fact able to discharge that duty. If we have this sense of duty, Kant claimed he did at least, to reach perfection, then we must be able to become perfect. And by perfection he means completely moral: doing everything from duty.
Kant says that it is obvious to us that, in the finite period of time allotted to us in this life, we could not perfect ourselves. Yet we have this duty, and everything we have the duty to do we could in fact do, Kant says that there must be an infinite amount of time to perfect ourselves. We cannot in this world. So we must live in another world after this.
This argument doesn’t add up. Do we actually have the obligation on ourselves to perfect ourselves? And does that mean that we would live forever in order to fulfill our duties? Kant even adds to this that there must be a God. After all, if we were perfect, then we must be rewards with complete happiness. Only an extraordinarily powerful being could give the kind of happiness you deserved if you became perfect. Kant says there is something to the logic of moral life that indicates God exists as the basis for rewards.
But this is an extraordinary set of doctrines! Yet this is the kind of confidence Kant has. Kant tells us that we can look within ourselves and discover duty: the duty of reason to fight passion, duty to fight desire, duty to fight inclination, and we even have the duty to completely perfect ourselves. This is a very austere view. Yet I find its austerity attractive. The arguments for immortality are unsound, but the austerity, the mere stoic sensibility, I find enlightening. The notion that reason would be caught up with moral duty, and that religion would arise out of a rational conception of moral duty, virtually unhinged the Romantic philosophers. Yet Kant’s self-defeating pronouncements make his philosophy unacceptable.