Mankind has found, over the centuries that certain rules of action best tend to promote the long-run happiness of both the individual and society. These rules of action have come to be called moral rules. Therefore, assuming that one seeks one's long-run happiness, these are the rules one ought to follow. Certainly this is the whole basis of what is called prudential ethics. In fact, wisdom, or the art of living wisely, is perhaps only another name for prudential ethics.
Prudential ethics constitutes a very large part of all ethics.
But the whole of ethics rests upon the same foundation. For men find that they best promote their own interests in the long run not merely by refraining from injury to their fellows, but by cooperating with them. Social cooperation is the foremost means by which the majority of us attain most of our ends. It is on the implicit if not the explicit recognition of this that our codes of morals, our rules of conduct, are ultimately based. We shall find also, when we have explored the subject further, that there are no irreconcilable conflicts between egoism and altruism, between selfishness and benevolence, between the long-run interests of the individual and those of society.