Aquinas’ treatise on conscience was the culmination of a lengthy debate that had been going on for centuries. This debate is today known and carried on under the name “weakness of the will” or akrasia. In my article, I am aiming to demonstrate that this discussion, which started with the Aristotle's problem of incontinent (akratic) man, has been going on through Augustine's problem of “two wills”. I would like to demonstrate that Aquinas links this discussion to his conception of the conscience and synderesis. Despite the fact, that R. Saarinen in his book about “weakness of the will” proves there is no connection between Aristotle's incontinent (akratic) man and Augustine's problem of “two wills”, my aim is to explain that it is Aquinas himself who connects Aristotle's incontinent man with Augustine's “two wills” and that incontinent person is someone who acts against his conscience.