 This thesis presents a challenge to certain natural and traditional ways of thinking about ethics. When we tell someone that he should not rob bank-vaults or murder bank-clerks, we usually understand ourselves to be telling him that he has reason not to rob bank-vaults or murder bank-clerks. If the internal reasons thesis is true, then the bank-robber can prove that he has no such reason simply by showing that he doesn’t care about anything that is achieved by abstaining from bank-robbing. So we seem to reach the disturbing conclusion that morality’s rules are like the rules of some sport or parlour-game—they apply only to those who choose to join in by obeying them.