Abstract: I argue that rationality can be used to mark a moral line human beings and at least the non-human animals that we breed to eat. I develop an account of the role of rationality in generating distinctive rights that does not have application to non-human animals, even though we do have obligations to them. I then consider the empirical evidence concerning animal psychology that bears on our moral relations to animals. In particular, I probe some central empirical issues about the rational capacities of animals, beginning with primates. I argue that it is at present unclear whether they have rational capacities. However, I then look at the empirical literature concerning the animals that we breed to eat, and here I argue that it is far clearer that they lack rational capacities. On this basis I argue that a moral line between human beings and non-human animals is a good one despite it being unclear in some places. That unclarity does not mean that there are not many cases that fall clearly one side or the other, which is what we need for action.