Strictly speaking, there are no such things as good and bad impulses. Think...of a piano. It has not got two kinds of notes on it, the 'right' notes and the 'wrong' ones. Every single note is right at one time and wrong at another. The Moral Law is not any one instinct or set of instincts: it is something which makes a kind of tune (the tune we call goodness or right conduct) by directing the instincts.