Altogether we may illustrate the relations of culture to environment by an analogy used by Dr. Wissler in another connection, which also brings us back to my initial analogy of the environmental theory with the associationist system in psychology. The environment furnishes the builders of cultural structures with brick and mortar but it does not furnish the architect’s plan. As the illustrations cited clearly prove, there is a variety of ways in which the same materials can be put together, nay, there is always a range of choice as regards the materials themselves. The development of a particular architectural style and the selection of a special material from among an indefinite number of possible styles and materials are what characterize a given culture. Since geography permits more than a single adjustment to the same conditions, it cannot give the interpretation sought by the student of culture. Culture can no more be built up of environmental blocks than can consciousness out of isolated ideas; and as the association of ideas already implies the synthetizing faculty of consciousness, so the assemblage and use of environmental factors after a definite plan already implies the selective and synthetic agency of a preëxisting or nascent culture. IV. THE DETERMINANTS OF CULTURE Psychology, racial differences, geographical environment, have all proved inadequate for the interpretation of cultural phenomena. The inference is obvious. Culture is a thing _sui generis_ which can be explained only in terms of itself. This is not mysticism but sound scientific method. The biologist, whatever metaphysical speculations he may indulge in as to the ultimate origin of life, does not depart in his workaday mood from the principle that every cell is derived from some other cell. So the ethnologist will do well to postulate the principle, _Omnis cultura ex cultura_.[1] This means that he will account for a given cultural fact by merging it in a group of cultural facts or by demonstrating some other cultural fact out of which it has developed. The cultural phenomenon to be explained may either have an antecedent within the culture of the tribe where it is found or it may have been imported from without. Both groups of determinants must be considered. The extraneous determinants of culture summed up under the heading of ‘diffusion’ or ‘contact of peoples’ have been repeatedly referred to in the preceding pages. A somewhat detailed examination seems desirable, for it is difficult to exaggerate their importance.