This paper intends to present the theoretic pathway that departs from the Freudian notion of unconscious and gets to the Lacanian concept of subject. Freud's first ideas regarding a neuron-based psychic apparatus were aligned with the premises of the modern science of his historical time, but his incipient theory ended up challenging some of the central premises of the modernity, like the Cartesian concept of a subject based on reason. Decades later, Lacan returned to Freud's work to look for the roots of the notion of subject in psychoanalysis and finally formalized a psychoanalytic definition of subject. The symbolic subject of the unconscious defined by Lacan becomes closer to the real as his teaching progressed. Unlike the univocal, rational subject proposed by Descartes, the development of the concept of subject in psychoanalysis established a divided being, made of language but also of jouissance, not entirely apprehended by the symbolic chain.