Condillac’s Treatise on Sensations constitutes a spectacular departure from Locke and expounds an original philosophy of consciousness and self-consciousness. Although there are other readings of the Treatise, this chapter sets out to investigate the relevance of the correspondence between Condillac’s analysis and contemporary naturalistic theories for his theses. Putting to one side Condillac’s principle of the sentiment-based logical “generation” of the faculties, which is alien to post-Darwinism, I will consider the different forms of self-knowledge identified by Condillac as conditions of the emergence of self-consciousness. The aim of this is to establish a criterion for self-knowledge. By cross-referencing and translating two languages, two eras and two traditions, the chapter will then proceed to the discussion of arguments and claims shared by Condillac and contemporary naturalists: first, the thesis that only human beings have self-consciousness; second, that humans share elementary self-relations with animals; and, third, that representations of one’s own body are essential to self-consciousness formation.