Alain Badiou’s theory of discipline condenses many important theoretical tools that he developed throughout his long encounter with various philosophical and political milieus from the mid 1960s to the mid 1980s, when he wrote his magnum opus _Being and Event_. Through this vast terrain, Badiou expressed seemingly different commitments: from logic and the epistemology of science in the late 1960s and politics during the 1970s, to ontology and mathematics in the 1980s, which has continued to this time. However, a close (...) reading of his major works during this period reveals an internal thread of thought that runs between them, which I have named discipline. In other words, discipline is the framework within which we can reconstruct Badiou’s main ideas as part of a continuous work (during the stated period) that not only reveals the internal coherence of his overall thought over the course of time, within which he showed different and seemingly unrelated commitments, but also gives us a powerful tool to understand the key concepts of his philosophy, such as the procedures of truth, ontology, phenomenology, and his commitment to axiomatic thinking. In this essay we aim to examine the concept of the subject in relation to the theory of discipline. We will do so by examining Badiou’s encounter with two crucial aspects of the theory of the subject discussed by Lacan: the Cartesian _cogito_ and the relation of the subject to the mathematical infinite. (shrink)