4. Kant claims that his categorical imperative is a moral principle that can be known purely by reason, without dependence on any observations or experience. It is a truth of reason that can be established in the same way we work out a proof in mathematics or geometry. If you were proposing a candidate for a moral principle known purely by reason, what do you think would be the best candidate? (You may think it is not possible to know moral truths purely by reason; perhaps you don't think moral truths can be known at all; maybe you doubt that any even exist. No matter. What sort of moral principle do you think would be most plausibly derived by pure reason?)