La morale et la science des moeurs, published in 1903, may appear to mark a sociological shift in the thinking of Lucien Lévy-Bruhl, and it partially prefigures his later works. This is nonetheless a philosophical or epistemological work addressed to philosophers and aimed at convincing them to give up constructing “theoretical moral systems” that cannot claim to be scientific and will necessarily be superceded by a sociological “moral science”. Well received by Durkheimian sociologists – though Durkheim himself was then giving up the kind of categorical opposition here systematized by Lévy-Bruhl – the work provoked numerous critical protests from philosophers. In 1906 Lévy-Bruhl himself synthesized these critiques and uncompromisingly refuted them. Thirty years later, Georges Gurvitch wrote a work affirming that, on the contrary, philosophical and sociological approaches to moral phenomena were complementary and both were necessary.