What are the determinants of culture? We have found that cultural traits may be transmitted from without and in so far forth are determined by the culture of an alien people. The extraordinary extent to which such diffusion has taken place proves that the actual development of a given culture does not conform to innate laws necessarily leading to definite results, such hypothetical laws being overridden by contact with foreign peoples. But even where a culture is of relatively indigenous growth comparison with other cultures suggests that one step does not necessarily lead to another, that an invention like the wheel or the domestication of an animal occurs in one place and does not occur in another. To the extent of such diversity we must abandon the quest for general formulæ of cultural evolution and recognize as the determinant of a phenomenon the unique course of its past history. However, there is not merely discontinuity and diversity but also stability and agreement in the sphere of culture. The discrete steps that mark culture history may not determine one another, but each may involve as a necessary or at least probable consequence other phenomena which in many instances are simply new aspects of the same phenomenon, and in so far forth one cultural element as isolated in description is the determinant or correlate of another. As for those phenomena which we are obliged to accept as realities without the possibility of further analysis, we can, at least, classify a great number of them and merge particular instances in a group of similar facts. Finally, there are dominant characteristics of culture, like cultural inertia or the secondary rationalization of habits acquired irrationally by the members of a group, which serve as broad interpretative principles in the history of civilization. In short, as in other sciences, so in ethnology there are ultimate, irreducible facts, special functional relations, and principles of wider scope that guide us through the chaotic maze of detail. And as the engineer calls on the physicist for a knowledge of mechanical laws, so the social builder of the future who should seek to refashion the culture of his time and add to its cultural values will seek guidance from ethnology, the science of culture, which in Tylor’s judgment is ‘essentially a reformer’s science.’ V. TERMS OF RELATIONSHIP