 The argument is clearly related to arguments from practicality against rationalism (see the  Anti-Rationalism Supplement).  The first premise postulates an internal connection between moral judgment and motivation. Weak Internalists believe, roughly, that judging that I morally ought to stop downloading movies entails that I have at least some motivation to stop downloading movies. Otherwise I don’t genuinely regard the action as morally wrong. My moral convictions are manifest in my motivational tendencies, if not always in action. Why? Basically, because the point of thinking in moral terms isn’t to discover some facts about the universe, but to get ourselves to act in ways that allow us to live together and reap the benefits of cooperation. Simon Blackburn (1988) and Allan Gibbard (1990) point out that any evolutionary benefits moral thought might have depend on its practicality. (See also Lenman (1999) and the entry on  Moral Motivation.)