In its widest acceptation, concupiscence is any yearning of the soul for good; in its strict and specific acceptation, a desire of the lower appetite contrary to reason.
To understand how the sensuous and the rational appetite can be opposed, it should be borne in mind that their natural objects are altogether different. The object of the former is the gratification of the senses; the object of the latter is the good of the entire human nature and consists in the subordination of reason to God, its supreme good and ultimate end.
But the lower appetite is of itself unrestrained, so as to pursue sensuous gratifications independently of the understanding and without regard to the good of the higher faculties. Hence desires contrary to the real good and order of reason may, and often do, rise in it, previous to the attention of the mind, and once risen, dispose the bodily organs to the pursuit and solicit the will to consent, while they more or less hinder reason from considering their lawfulness or unlawfulness.
This is concupiscence in its strict and specific sense. As long, however, as deliberation is not completely impeded, the rational will is able to resist such desires and withhold consent, though it be not capable of crushing the effects they produce in the body, and though its freedom and dominion be to some extent diminished.
If, in fact, the will resists, a struggle ensues, the sensuous appetite rebelliously demanding its gratification, reason, on the contrary, clinging to its own spiritual interests and asserting it control.** âThe flesh lusteth against the spirit, and the spirit against the flesh.â**