Franz Boas (1920) talks about two distinct theories; the Cultural evolution and the cultural diffusion on this article. The hypothesis for cultural evolution has logical flow in its arguments. The cultural life of mankind follows definite laws which are applicable everywhere among all the races and all the people. But in other hand, similarities of development in the remote parts of the globe is rejected and in its place it is assumed that identical development in two different part of the world must always be due to migration and diffusion. These two distinct theories and their methods basically form classification of a culture. According to Boas, cultures can only be understood with reference to their particular historical development, it means history and it should have the empirical data is main thing for him. And also the cultural evolution cannot be explained only by the theory; it needs proper methodology in the particular culture. So according to Boas, Culture can only be understood by empirical data with proper method to its own particular historical development.
Boas, Franz (1920) “The Methods of Ethnology,” in McGee, R. J and R. L. Warms (eds.) (2003) Anthropology Theory: An Introductory History, Boston: McGraw-Hill pp. 121-128.