Psychological egoism is the view that people are always selfish. When was the last time you did a good deed? Did you do it for its own sake, or for your own? The egoist says that all of us are necessarily self-regarding. I shall argue that this view is incorrect.
First we should ask, what kind of claim is this? Is it an a priori claim, or a generalization from experience? If it were the latter, we could never conclusively prove it: we could never show that necessarily all actions are selfish. So it must be a priori. But no a priori claim could be substantive: a priori truths are all analytic (that is, the predicate is contained in the subject). So if this claim were analytic, it would become trivial. (It is worth noting that Kripke's claim that there are a posteriori necessary truths does not show that a priori truths are not analytic.)
The situation is paralleled by pseudo-sciences such as Freudian psychoanalysis. As Karl Popper has argued, any theory can be maintained so long as it is drained of empirical content. Like psychoanalysis, psychological egoism makes no genuine claims and can never be refuted. But it purchases certainty at the price of becoming vacuous. I shall have more to say on this below.
The simplest way to see the egoist's mistake is to distinguish between the side-effects of an action and the reason for which it was done. Suppose we grant that in doing a good deed, we usually get a pleasant feeling (though I suspect this is false). Even so, this would not show that that feeling was indeed the motivating factor in our behavior; it could simply be a side effect of doing the good deed. Compare the case in which someone types for...