 One further point should be made about our reasons for supposing that there is such a thing as altruism. Just as we can ask, “what entitles us to believe that altruism exists?” so we can ask: “what entitles us to believe that egoism exists?” Consider the possibility that whenever we act for our own good, we are not doing so only for our own sake, but also for the sake of someone else. On what grounds are we entitled to reject that possibility?