This thesis aims at examining ancient akrasia and contemporary weakness of will. The contemporary problem of weakness of will is rooted on the phenomenon called akrasia since Aristotle s Ethics. Traditionally, the history of philosophy depicts the continuity of the same essential philosophical problem. The initial inquiry on contemporary weakness of will in Richard M. Hare and Donald Davidson renewed the ancient akrasia debate as presented in Plato and Aristotle. Nevertheless, there is a fundamental distinction between both phenomena: while weakness of will reflects only action contrary to better judgement, akrasia refers to submission of reason to irrational impulses. My present thesis aims at establishing that there are two distinct philosophical problems: the ancient problem of akrasia in the face of moral knowledge and the contemporary problem of irrational action against better judgment. Indeed, analytic reception of ancient akrasia in Plato and Aristotle marks the reestablishment of contemporary weakness of will on the works of Hare and Davidson. My research plan examines the underlying relation between ancient akrasia and contemporary weakness of will. Therefore, the thesis is divided in two parts. In the first part, I look into ancient akrasia s internal conflict and the status of moral knowledge in Plato and Aristotle s Ethics. In the second part, reception of ancient akrasia in the works of Hare and Davidson informs the emergence of the original formulation of contemporary weakness of will on practical conflict of irrational action against better judgement.