 Of the three forms of psychological egoism distinguished above, the one that is least open to objection is the weak form that holds that altruism is never pure. It claims that whenever we act, one of our motives is a desire for our own good. There is no good a priori argument for this thesis—or, at any rate, the a priori argument we have been considering for the strongest form of psychological egoism does not support it, because the two premises used in that argument are so implausible. But it might nonetheless be suggested that as a matter of fact we always do find some self-interested motivation that accompanies altruistically motivated behavior. It is difficult to refute that proposal. We should not pretend that we know all of the considerations and causes that underlie our behavior. Some of our motives are hidden, and there is too much going on in our minds for us to be aware of the whole of our psychology. So, for all we know, we might never be pure altruists.