Charity is not a potency of the soul, because if it were it would be natural. Nor is it a passion, because it is not in a sensitive potency in which are all passions. Nor is it a habit, because a habit is removed with difficulty; charity, however, is easily lost through one act of mortal sin. Therefore charity is not something created in the soul.

On Charity: (De Caritate) (ed. 1960)