Ryle's distinction between knowing that and knowing how has recently been challenged.The paper first briefly defends the distinction and then proceeds to address the question of classifying moral knowledge.Moral knowledge is special in that it is practical,that is,it is essentially a motive.Hence the way we understand moral knowledge crucially depends on the way we understand motivation.The Humean theory of motivation is wrong in saying that reason cannot be a motive,but right in saying that desire is essential for motivating us.The right response to the Humean theory of motivation is to see that moral knowledge is desire-related rationality or thought-related desire.Moral knowledge is neither knowing that nor knowing how but rather a third species of knowledge which we may call “knowing to do.” Knowing to do is to be rationally disposed to do the right thing.This understanding of moral knowledge is exactly what we can learn from Aristotle's ethics.