The sacred is the key to Durkheim's argument. Consequently, Book I of The Elementary Forms, consists of an extensive consideration and criticism of various theories of the origin of the distinction between the sacred and the profane. Durkheim defines religion, criticizes Animism and Naturism, and then offers Totemism as an answer to the question of where the idea of the sacred comes from. As Totemism will provide the focal point of Durkheim's argument, his arguments with regard to Totemism are of particular importance.

Durkheim's emphasis on the sacred, combined with a lengthy review of various theories regarding the origin of the idea of the sacred, has tended to create the impression that his focus is on religion, and the relationship between the variety of religious beliefs and classifications in particular societies. In fact, however, the distinction between sacred and profane, and the critical review of the anthropology of religion that occupy Book I are essential to Durkheim's epistemological argument. The first dualism, sacred versus profane, turns out also to be the first classification. As the first type of moral force it not only constitutes classification as the first category of the understanding, but is also an essential component of the enactment of all the other categories. Without the enacted “feeling” of the sacred, moral force cannot be created, categories of reason cannot be developed, and society, as a consequence, cannot exist.

Classification is the first category that Durkheim considers in any detail in The Elementary Forms.