It is therefore evident that all passions that are a cause of sin can be reduced to these three:  since all the passions of the concupiscible part can be reduced to the first two, and all the irascible passions to the third, which is not divided into two because all the irascible passions conform to spiritual concupiscence.

Reply Obj. 1:  “Pride of life” is included in covetousness according as the latter denotes any kind of appetite for any kind of good.  How covetousness, as a special vice, which goes by the name of “avarice,” is the root of all sins, shall be explained further on (Q. 84, A. 1).

Reply Obj. 2:  “Concupiscence of the eyes” does not mean here the concupiscence for all things which can be seen by the eyes, but only for such things as afford, not carnal pleasure in respect of touch, but in respect of the eyes, i.e. of any apprehensive power.

Reply Obj. 3:  The sense of sight is the most excellent of all the senses, and covers a larger ground, as stated in Metaph. i:  and so its name is transferred to all the other senses, and even to the inner apprehensions, as Augustine states (De Verb.  Dom., serm. xxxiii).

Reply Obj. 4:  Avoidance of evil is caused by the appetite for good, as stated above (Q. 25, A. 2; Q. 39, A. 2); and so those passions alone are mentioned which incline to good, as being the causes of those which cause inordinately the avoidance of evil. ________________________

SIXTH ARTICLE [I-II, Q. 77, Art. 6]

Whether Sin Is Alleviated on Account of a Passion?

Objection 1:  It would seem that sin is not alleviated on account of passion.  For increase of cause adds to the effect:  thus if a hot thing causes something to melt, a hotter will do so yet more.  Now passion is a cause of sin, as stated (A. 5).  Therefore the more intense the passion, the greater the sin.  Therefore passion does not diminish sin, but increases it.

Obj. 2:  Further, a good passion stands in the same relation to merit, as an evil passion does to sin.  Now a good passion increases merit:  for a man seems to merit the more, according as he is moved by a greater pity to help a poor man.  Therefore an evil passion also increases rather than diminishes a sin.

Obj. 3:  Further, a man seems to sin the more grievously, according as he sins with a more intense will.  But the passion that impels the will makes it tend with greater intensity to the sinful act.  Therefore passion aggravates a sin.

On the contrary, The passion of concupiscence is called a temptation of the flesh.  But the greater the temptation that overcomes a man, the less grievous his sin, as Augustine states (De Civ.  Dei iv, 12).

I answer that, Sin consists essentially in an act of the free will, which is a faculty of the will and reason; while passion is a movement of the sensitive appetite.  Now the sensitive appetite can be related to the free-will, antecedently and consequently:  antecedently, according as a passion of the sensitive appetite draws or inclines the reason or will, as stated above (AA. 1, 2; Q. 10, A. 3); and consequently, in so far as the movements of the higher powers redound on to the lower, since it is not possible for the will to be moved to anything intensely, without a passion being aroused in the sensitive appetite.