outer changes and works in the body adapted changes, the implication being that psychology becomes a science, as fast as these relations of phenomena are explained as consequences of ultimate principles. Sociology, too, represented down to recent times only by stray ideas about social organisation, scattered through the masses of worthless gossip furnished us by historians, is coming to be recognised by some as also a science; and such adumbrations of it as have from time to time appeared in the shape of empirical generalisations, are now beginning to assume the character of generalisations made coherent by derivation from causes lying in human nature placed under given conditions. Clearly then, _ethics, which is a science dealing with the conduct of associated human beings_, regarded under one of its aspects, has to undergo a like transformation, and, at present undeveloped, can be considered a developed science only when it has undergone this transformation. "A preparation in the simpler sciences is pre-supposed. Ethics has a physical aspect, since it treats of human activities, which, in common with all expenditures of energy, conform to the law of the persistence of energy; moral principles must conform to physical necessities. It has a biological aspect, since it concerns certain effects, inner and outer, individual and social, of the vital changes going on in the highest type of animal. It has a psychological aspect, for its subject matter is an aggregate of actions that are prompted by feelings and guided by intelligence. And it has a sociological aspect, for these actions, some of them directly, and all of them indirectly, affect associated beings. "What is the implication? Belonging under one aspect to each of these sciences--physical, biological, psychological, sociological--it can find its ultimate interpretations only in those fundamental truths which are common to all of them. Already we have concluded in a general way that conduct at large, including the conduct Ethics deals with, is to be fully understood only as an aspect of evolving life; and now we are brought to this conclusion in a more special way. "Here, then, we have to enter on the consideration of moral phenomena as phenomena of evolution; being forced to do this by finding that they form a part of the aggregate of phenomena which evolution has wrought out. If the entire visible universe has been evolved--if the solar system as a whole, the earth as part of it, the life in general which the earth bears, as well as that of each individual organism--if the mental phenomena displayed by all creatures, up to the highest, in common with the phenomena presented by aggregates of these highest--if one and all conform to the laws of evolution; then the necessary implication is that those phenomena of conduct in these highest creatures with which morality is concerned, also conform."[3]