Practical reason to Kant does not mean the kind of reason that tells us how to make a boat in our basement, or how to get more pecans from the tree in our yard. Rather it has to do with praxis (πρᾶξις) or action, specifically choosing a course of action. It is basically about ethics.
Kant considers several ways derive an ethical basis for action, and he denies the idea that a man should act for his own happiness. This appears to put him at odds with both Aristotle and Ayn Rand, who both believed that we should act to maximize our happiness. Kant ultimately says that we should we act as if we were legislating all men. Could all men (and women) act as I do without it ending in a contradiction. If all men were to lie, I would be unable to believe anyone, and there would be a contradiction involved.
What Kant does not do is question whether all actions are moral, and are susceptible to moral evaluation? If I make a cup of coffee, do I perform a moral act, or is it morally indifferent whether I make a cup of coffee or not? To make a cup of coffee for the purpose of throwing it in my neigbor's face is clearly immoral, but is the action, exclusive of the assault, and assuming that it was properly used, moral or immoral in itself? Sartre once claimed that when I make a cup of coffee that I legislate for the world, is that true?
Kant takes what is known as a deontological approach, he believes that we have a duty to perform certain actions. So we have a duty to justice, and we have a duty to truth. What happens though when these duties come into conflict? It is not just that a person should die from persecution for their religion. So if you're an Elizabethan Catholic and the watch comes looking for a priest who has just said Mass in your house, do you deny that the priest is hiding in his little hole, or do you point, and say
There he is?
St. John XXIII forged baptismal records for Jews. Did his duty to protect innocents override his duty to the truth?
Another problem that arises is the maxim that is used as the basis for generalizing. If one assumes that the maxim for an action is
All men should form homosexual unions, that obviously results in species ending events, and is immoral. If the maxim is
All men of homosexual inclination should choose as I do, the action is universalized to a set of the people contained within
all men, while still having the form of a universal. So which is the maxim to be evaluated?
Kant also re-instantiates God, free will, and immortality as ideas of practical reason. They are intimately connected with Kant's ethical program, and constitute a necessary, but non-provable part of it.
I'm afraid that my posts on Kant aren't all that satisfying to me. I'm not sure that I fully understand much of what he's saying, and I may re-read the critiques several more times before I pass over into senility.
Next up will be other some plays by Shakespeare & others, or Boswell's account of his first year in London.