Insunt ut in via ad naturam, as one might say of an undergraduate inest ut in via ad gradum. "A habit is a quality difficult to change, whereby an agent, whose nature it was to work one way or another indeterminately, is disposed easily and readily at will to follow this or that particular line of action. Habit differs from disposition, as disposition is a quality easily changed. Thus one in a good humour is in a disposition to be kind. Habit is a part of character: disposition is a passing fit" (Ethics and Natural Law, p. 64). Unfortunately, the word disposition in English is used to signify natural or congenital character, the Latin indoles. We might perhaps say mood. But the plural, good dispositions, expresses St Thomas's dispositio.
Of God and His Creatures: 3.65