Scientists have often claimed that scientific knowledge itself, when fully grasped, will generate the rules of proper human conduct. Beginning with Socrates' doctrine that knowledge is virtue they have endeavored through the ages to squeeze the is, hoping that it would yield an ought. The futility of such an undertaking needs to be unmasked and clearly exposed to view; for it involves the naturalistic fallacy which has been rightly criticised by many writers. To put it simply: even if we knew everything about the physical universe, about human physiology, about man's natural dispositions, his drives, his instincts and his normal reaction to all stimuli; even if we could predict how average men will in scientific fact behave under all specified circumstances (at a given time of the evolutionary process), we should still have no basis for judging the moral quality of his actions. Even if the drive for survival or for individual happiness were absolutely universal we could still not prove, by using the laws of science, that man ought not to die or ought to be unhappy in certain situations. This absence of affinity between the substance of science and the substance of ethics must be recognized at the outset. Although I shall suggest in the sequel that we are in possession of principles which may, if properly applied, engender facilities for judging objectively the moral behavior of men, and to judge them independently of local standards of value, I do not refer to any generalizations of scientific fact.