A common assumption is that psychological egoism, the view that a person can do an act only if she believes that the act is in her interest, combined with ought-implies-can, the view that a person morally ought to do an act only if she can do it, entails the view – call it OIB – that a person morally ought to do an act only if she believes that the act is in her interest. I argue that psychological egoism and ought-implies-can, interpreted fairly, use “can” in different ways; consequently, they do not entail OIB. They entail something similar to OIB, but not OIB itself. From these facts several significant results follow, each concerning arguments or assumptions about psychological, ethical, or rational egoism. For instance, they undermine the view that psychological egoism rules out those other two forms of egoism.
