Listers, a portion of St. Thomas Aquinas’ brilliance is attributed to his ability to state that which we all already know but struggle to articulate. The question Is lust a sin? seems absurd, but by asking these questions and answering them in thomistic fullness the Angelic Doctor is able to lead us into profound observations. Similar to his treatment on the capital vice of gluttony, the beloved “Dumb Ox” echoes the seriousness in which Christ took the reality of sin and how it perverts what is good and reasonable in humanity.

St. Thomas Aquinas, the Angelic Doctor, whose virtue warms the world.

1. What is the proper matter of lust?

The Common Doctor begins his treatment of lust by discerning its “matter” or what properly composes the vice of lust.

As Isidore says (Etym. x), “a lustful man is one who is debauched with pleasures.” Now venereal pleasures above all debauch a man’s mind. Therefore lust is especially concerned with such like pleasures.

The Angelic Doctor turns to the authority of St. Isidore of Seville (d. AD 560)1 and agrees the lustful man is “debauched with pleasures.” However, exactly what pleasures compose the matter of lust? Lust is contrary to the virtue of temperance, which holds us to right reason in the midst of that which would lure us away – yet how is it different than greed or gluttony?

Even as temperance chiefly and properly applies to pleasures of touch, yet consequently and by a kind of likeness is referred to other matters, so too, lust applies chiefly to venereal pleasures, which more than anything else work the greatest havoc in a man’s mind, yet secondarily it applies to any other matters pertaining to excess. Hence a gloss on Galatians 5:19 says “lust is any kind of surfeit.”

To wit, lust applies primarily to venereal pleasures and secondarily to other pleasures.

The Sacrament of Holy Matrimony

2. Are all sexual acts lustful?

Listers, Aquinas commonly submits questions that seem strange or even absurd. Some questions seem superfluous and others seem so obvious that they need not be asked. However, the Summa Theologica is not an encyclopedia, but a pedagogical series of questions that build upon one another. This question’s official title is Whether no venereal act can be without sin? and it lays the groundwork to understand the more complex questions and answers.

A sin, in human acts, is that which is against the order of reason. Now the order of reason consists in its ordering everything to its end in a fitting manner. Wherefore it is no sin if one, by the dictate of reason, makes use of certain things in a fitting manner and order for the end to which they are adapted, provided this end be something truly good.

Virtue is a good habit or that which disposes us to good acts through the perfection of our powers. One such power is our reason and virtue perfects the power of our reason, e.g., temperance holds us to reason when faced with pleasures that would lure us from reason.2

Vices are those habits which would disorder our reason. If temperance is the virtue that holds us to right reason even in the midsts of allurement – in distinction to fortitude which holds us to reason in the midst of fear – the the vice of lust seeks to pervert that which is good and reasonable through venereal matters.3

Now just as the preservation of the bodily nature of one individual is a true good, so, too, is the preservation of the nature of the human species a very great good. And just as the use of food is directed to the preservation of life in the individual, so is the use of venereal acts directed to the preservation of the whole human race.

Hence Augustine says (De Bono Conjug. xvi): “What food is to a man’s well being, such is sexual intercourse to the welfare of the whole human race.” Wherefore just as the use of food can be without sin, if it be taken in due manner and order, as required for the welfare of the body, so also the use of venereal acts can be without sin, provided they be performed in due manner and order, in keeping with the end of human procreation.

Sex is good and serves a mighty and noble purpose within the human race. Lust however seeks to corrupt man’s reasoning toward sex and distort its goodness.

 

Lust in Dante’s Inferno by Gustave Dore

3. Why is lust a sin?

In his question Whether the lust that is about venereal acts can be a sin? the Common Doctor of the Church builds upon the foundation already laid.

The more necessary a thing is, the more it behooves one to observe the order of reason in its regard; wherefore the more sinful it becomes if the order of reason be forsaken. Now the use of venereal acts, as stated in the foregoing Article, is most necessary for the common good, namely the preservation of the human race.

Wherefore there is the greatest necessity for observing the order of reason in this matter: so that if anything be done in this connection against the dictate of reason’s ordering, it will be a sin. Now lust consists essentially in exceeding the order and mode of reason in the matter of venereal acts. Wherefore without any doubt lust is a sin.

Evil is not a thing in itself, but is rather a lack or an absence of what is good. Aquinas would say evil is the privation of the good. In that line of thinking, if right reason is a good and sin is an evil then being sinful is irrational and a strike against reason. Lust then carries a particular weightiness about it due to human sexuality’s strong connection with the common good. The seriousness imported by the corruption of lust is the basis of Aquinas’ next question.

 

Virtue perfects our reason and the vices incline humanity to the irrational and the disorder. It is humanity’s choice. Dante’s inferno – “Dante and Virgil in hell” (1850) by William Bouguereau.

4. Is lust a capital vice?

Flowing with the logical progression of St. Thomas’ previous questions, it is no surprise that Aquinas cites the authority of Pope St. Gregory the Great in naming lust a capital or “deadly” vice.

Gregory (Moral. xxxi, 45) places lust among the capital vices.

As stated above, a capital vice is one that has a very desirable end, so that through desire for that end, a man proceeds to commit many sins, all of which are said to arise from that vice as from a principal vice. Now the end of lust is venereal pleasure, which is very great. Wherefore this pleasure is very desirable as regards the sensitive appetite, both on account of the intensity of the pleasure, and because such like concupiscence is connatural to man. Therefore it is evident that lust is a capital vice.

Like virtues, vices are habits and habits are a quality that define who we are. As virtues produce in us many good works so too do vices become sordid sources of many sins. Lust is a capital vice because it manifests sins within the matter of man’s strong desire for venereal pleasures and that venereal pleasure in and of itself is a good when properly ordered to reason.

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  1. Isidore: Born at Cartagena, Spain, about 560; died 4 April, 636. Isidore was the son of Severianus and Theodora. His elder brother Leander was his immediate predecessor in the Metropolitan See of Seville; whilst a younger brother St. Fulgentius presided over the Bishopric of Astigi. His sister Florentina was a nun, and is said to have ruled over forty convents and one thousand religious. Source []
  2. What is a habit? –  The Philosopher (Aristotle) “defines habit, a ‘disposition whereby someone is disposed, well or ill;’ and he says that by ‘habits we are directed well or ill in reference to the passions.’ For when a the mode is suitable to the thing’s nature, it has the aspect of good: and when it is unsuitable, it has the aspect of evil.” (I-II.49)

    A Habit or Act? –  Virtue “denotes a certain perfection of a power. Now a thing’s perfection is considered chiefly in regard to its end. But the end of power is act. Wherefore power is said to be perfect, according as it is determinate to its act.” Power (potential) finds its end in an act. Virtue perfects the power; thus, the act is perfected. Justice is not an act, but by the habit of justice one may act justly. – More on Virtue from Aquinas []

  3. Temperance v. Fortitude: In clarification by contrast, temperance would be the virtue that keeps us from adultery, masturbation, and any disordered sexual pleasure, while fortitude holds us to reason in the midst of fear, e.g., on the battlefield, when scared to do what is right and good, etc. []