Conditions of mortal sin: knowledge, free will, grave matter
Contrary to the teaching of Baius (prop. 46, Denzinger-Bannwart, 1046) and the Reformers, a sin must be a voluntary act. Those actions alone are properly called human or moral actions which proceed from the human will deliberately acting with knowledge of the end for which it acts. Man differs from all irrational creatures in this precisely that he is master of his actions by virtue of hisreason and free will (I-II:1:1). Since sin is a human act wanting in due rectitude, it must have, in so far as it is a human act, the essential constituents of a human act. The intellect must perceive and judge of the morality of the act, and the will must freely elect. For a deliberate mortal sin there must be full advertence on the part of the intellect and full consent on the part of the will in a grave matter. An involuntary transgression of the law even in a grave matter is not a formal but a material sin. The gravity of the matter is judged from the teaching of Scripture, the definitions ofcouncils and popes, and also from reason. Those sins are judged to be mortal which contain in themselves some grave disorder in regard to God, our neighbour, ourselves, or society. Some sins admit of no lightness of matter, as for example, blasphemy, hatred of God; they are always mortal (ex toto genere suo), unless rendered venial by want of full advertence on the part of theintellect or full consent on the part of the will. Other sins admit lightness of matter: they are grave sins (ex genere suo) in as much as their matter in itself is sufficient to constitute a grave sin without the addition of any other matter, but is of such a nature that in a given case, owing to its smallness, the sin may be venial, e.g. theft.