 Since we have distinguished several different ways of using the term “altruism”, it will be helpful to make similar distinctions between different varieties of psychological egoism. Recall that an act is altruistic in the weak sense if it is motivated, at least in part, by the fact that it benefits someone else (or the fact that it will not injure anyone else). Psychological egoism, as defined in the preceding paragraph, denies that altruism in this sense exists. That is the strongest form of this doctrine; it is usually what philosophers have in mind when they discuss psychological egoism. But we can imagine weaker versions. One of them would deny that altruism is ever pure; it would say, in other words, that whenever we act, one of our motives is a desire for our own good. Another weaker form of psychological egoism would hold that we never voluntarily do what we foresee will sacrifice our well-being to some extent. This third form of psychological egoism would admit that sometimes one of our reasons for acting is the good we do for others for their sake; but it claims that we never act for the good of others when we think that doing so would make us worse off.