Objection 1. It would seem that weakness, ignorance, malice and concupiscence are not suitably reckoned as the wounds of nature consequent upon sin. For one same thing is not both effect and cause of the same thing. But these are reckoned to be causes of sin, as appears from what has been said above (76, 1; 77, A3,5; 78, 1). Therefore they should not be reckoned as effects of sin.
Objection 2. Further, malice is the name of a sin. Therefore it should have no place among the effects of sin.
Objection 3. Further, concupiscence is something natural, since it is an act of the concupiscible power. But that which is natural should not be reckoned a wound of nature. Therefore concupiscence should not be reckoned a wound of nature.
Objection 4. Further, it has been stated (77, 3) that to sin from weakness is the same as to sin from passion. But concupiscence is a passion. Therefore it should not be condivided with weakness.
Objection 5. Further, Augustine (De Nat. et Grat. lxvii, 67) reckons "two things to be punishments inflicted on the soul of the sinner, viz. ignorance and difficulty," from which arise "error and vexation," which four do not coincide with the four in question. Therefore it seems that one or the other reckoning is incomplete.
On the contrary, The authority of Bede suffices [Reference not known].
I answer that, As a result of original justice, the reason had perfect hold over the lower parts of the soul, while reason itself was perfected by God, and was subject to Him. Now this same original justice was forfeited through the sin of our first parent, as already stated (81, 2); so that all the powers of the soul are left, as it were, destitute of their proper order, whereby they are naturally directed to virtue; which destitution is called a wounding of nature.
Again, there are four of the soul's powers that can be subject of virtue, as stated above (Question 61, Article 2), viz. the reason, where prudence resides, the will, where justice is, the irascible, the subject of fortitude, and the concupiscible, the subject of temperance. Therefore in so far as the reason is deprived of its order to the true, there is the wound of ignorance; in so far as the will is deprived of its order of good, there is the wound of malice; in so far as the irascible is deprived of its order to the arduous, there is the wound of weakness; and in so far as the concupiscible is deprived of its order to the delectable, moderated by reason, there is the wound of concupiscence.
Accordingly these are the four wounds inflicted on the whole of human nature as a result of our first parent's sin. But since the inclination to the good of virtue is diminished in each individual on account of actual sin, as was explained above (Question 1, Article 2), these four wounds are also the result of other sins, in so far as, through sin, the reason is obscured, especially in practical matters, the will hardened to evil, good actions become more difficult and concupiscence more impetuous.
Reply to Objection 1. There is no reason why the effect of one sin should not be the cause of another: because the soul, through sinning once, is more easily inclined to sin again.
Reply to Objection 2. Malice is not to be taken here as a sin, but as a certain proneness of the will to evil, according to the words of Genesis 8:21: "Man's senses are prone to evil from his youth" [Vulgate: 'The imagination and thought of man's heart are prone to evil from his youth.'].
Reply to Objection 3. As stated above (82, 3, ad 1), concupiscence is natural to man, in so far as it is subject to reason: whereas, in so far as it is goes beyond the bounds of reason, it is unnatural to man.
Reply to Objection 4. Speaking in a general way, every passion can be called a weakness, in so far as it weakens the soul's strength and clogs the reason. Bede, however, took weakness in the strict sense, as contrary to fortitude which pertains to the irascible.
Reply to Objection 5. The "difficulty" which is mentioned in this book of Augustine, includes the three wounds affecting the appetitive powers, viz. "malice," "weakness" and "concupiscence," for it is owing to these three that a man finds it difficult to tend to the good. "Error" and "vexation" are consequent wounds, since a man is vexed through being weakened in respect of the objects of his concupiscence.
Source: Summa Theologica (New Advent)