This study is concerned with Augustine's use of habit (consuetudo) to explain man's reluctance to raise his mind to God, and his difficulty in doing good. In the books that will be examined here, consuetudo is nearly always used in a pejorative sense, and can thus be translated as bad habit (be it of a psychological or ethical nature). Habit as a formal instrument of thought was known to Augustine early in his life from a reading of the Categories. There he learned that habit was a quality of a substance, not a substance itself: ‘One kind of quality let us call habits ἕξιϛ and conditions (διάθεσις). A habit differs from a condition in being more stable and lasting longer. Such are the branches of knowledge and the virtues. Justice, temperance, and the rest seem to be not easily changed.’ Augustine was also aware of the idea of habit as a second nature (consuetudo secunda natura), i.e. a tendency which is created by one's own activity, and which in turn produces effects in a predictable sort of way. This idea was a commonplace of the ancient world, and may have come to Augustine through the professors of rhetoric, who taught speech and composition through the inculcation of good habits.