Durkheim was very fond of three-part schemas, perhaps due to his training at the École Normale Superieure and in philosophy. His three great works The Division of Labor (1893), Suicide (1897) and The Elementary Forms of Religious Life (1912) are each composed of three “books” (setting aside The Rules of Sociological Method (1895), a methodological manifesto, first published in article form). The influence of this ternary rhetoric can be perceived right at the heart of his scientific work. Thus in his first major book, Durkheim identifies three abnormal forms of the division of labor; similarly in Suicide, he distinguishes three types of suicide. But this is only an illusion. In both cases Durkheim presents three types but, if one reads properly, he describes four. Beneath the appearance of a triangle there is a square, and this square is logically necessary to Durkheim's reasoning and the coherence of his analysis. These two squares, one for abnormal forms of the division of labor, the other for types of suicide, will be briefly reviewed before returning to the thorny question of their possible relationships.