It is not pretended that a moral theory based upon realities of human nature and a study of the specific connections of these realities with those of physical science would do away with moral struggle and defeat. It would not make the moral life as simple a matter as wending one's way along a well-lighted boulevard. All action is an invasion of the future, of the unknown. Conflict and uncertainty are ultimate traits. But morals based upon concern with facts and deriving guidance from knowledge of them would at least locate the points of effective endeavor and would focus available resources upon them. It would put an end to the impossible attempt to live in two unrelated worlds. It would destroy fixed distinction between the human and the physical, as well as that between the moral and the industrial and political. A morals based on study of human nature instead of upon disregard for it would find the facts of man continuous with those of the rest of nature and would thereby ally ethics with physics and biology. It would find the nature and activities of one person coterminous with those of other human beings, and therefore link ethics with the study of history, sociology, law and economics. Such a morals would not automatically solve moral problems, nor resolve perplexities. But it would enable us to state problems in such forms that action could be courageously and intelligently directed to their solution. It would not assure us against failure, but it would render failure a source of instruction. It would not protect us against the future emergence of equally serious moral difficulties, but it would enable us to approach the always recurring troubles with a fund of growing knowledge which would add significant values to our conduct even when we overtly failed--as we should continue to do. Until the integrity of morals with human nature and of both with the environment is recognized, we shall be deprived of the aid of past experience to cope with the most acute and deep problems of life. Accurate and extensive knowledge will continue to operate only in dealing with purely technical problems. The intelligent acknowledgment of the continuity of nature, man and society will alone secure a growth of morals which will be serious without being fanatical, aspiring without sentimentality, adapted to reality without conventionality, sensible without taking the form of calculation of profits, idealistic without being romantic. PART ONE THE PLACE OF HABIT IN CONDUCT I