The Parts of Lust


As is no doubt evident from many of my other writings, I am a great admirer of St. Thomas Aquinas. I even ended up making a section in my library devoted to books by him, about him and those related to various extensions of Thomistic thought.

The Dumb Ox, as he was nicknamed by his teacher Albert the Great, is one of, if not the most influential theologian and philosopher in Christian history. His seminal work, the Summa Theologiae, while certainly something of a synthesis between Aristotelian and Christian thought, is actually much more interesting, for we find in the very structure of the Summa an insight into the very mind of the author itself, both rigorous in its method and vast-reaching in its scope.

A brief overview of the structure of the Summa can be found below.

For those unacquainted with the structure of the Summa, Aquinas develops his arguments and syntheses by means of various Questions grouped into articles. Each Question is a sort of thematic grouping for a specific topic, and then the various articles are different approaches to that topic. For example, Question 153 in the Second Part of the Second Part of the Summa concerns Lust, while Article 1 of Question 153 asks “Whether the matter of lust is only venereal desires and pleasures?”

Each Article then begins not with Aquinas’ own answer, but rather by listing a number of objections to his eventual answer. What is fascinating about his approach is the sheer intellectual honesty he brings to bear upon his work, for the objections that he raises are not mere straw-men, but are rather pulled from eminent authorities. Although the objections are somewhat distinct, the listings all begin with ‘it would seem that’ and then build upon each other, constructing a counter-argument.

Following the listing of the objections is the sed contra– on the contrary- in which Aquinas offers what will be a contrary answer to the question, generally buttressed by an authority of its own.

One thing that should be noted about the scholastic method in general is that it was axiomatic that an argument from authority is not actually an argument. Aquinas’ point in this structure seems to be to demonstrate this as fully as possible, since authorities of the same weight can be set against each other in regards to different questions.

Aquinas’ mind on a question is not revealed until the section that begins with ‘I answer that,’ wherein his own position is set forth. Generally this position is opposed to the objections and is in broad agreement with the sed contra, but not always. What is more important is that when he does quote authorities in support, it is done for corroboration, rather than for substantiation. In other, words, he is demonstrating that his argument does not ultimately rely upon their testimony, but neither is it necessarily novel.

The final sections are specific replies to (usually) each Objection. Much of the time he doesn’t necessarily disagree with the Objection but rather with a particular understanding or presentation of it. While an Objection may present one way of seeing something, he often considers if there is not another sense in which it could be understood and thus compatible with his answer. In this manner he is generally quite charitable, allowing that argumentation can be broader than it is often couched. However, in some cases where an authority is used, he will often quote that same authority in response to himself or as a means of clarifying the statement.

It can be tempting to skip immediately to Aquinas’ ‘I answer that,’ but this is to miss the whole point of the structure of the Summa. By building objection upon objection in the opening, Aquinas is seeking to build a strong contrary case, one that can be understood as both reasonable and having substantial agreement in various authorities. In meeting it head on and responding to each objection in turn, he attempts to actually demonstrate the superiority of his argument, rather than simply asserting something contrary.

In this respect each Summa is like a battle of wits, all the more remarkable for being carried out by one individual. We see in the process a man who is always engaged in self-critique, searching out the reasons behind what he thinks and what he believes, not taking their pedigree for granted but subjecting them to rigors of the dialectic.

Sex, Sex, Sex

Aquinas may have been cloistered, but he was no stranger to the world or the vexing questions that swirl around issues which still vex us today, including those relating to human sexuality. Aquinas himself seems to have wanted to be a monk from the get-go- against his family’s wishes- and even when his brothers locked him in a tower with a temptress he was so committed to his future vocation that he grabbed a brand from the fire to keep her at bay. This sort of imprisonment and temptation went on for two years, but he never relented, finally released to pursue the monastic life.

The Summa Theologiae ends up covering a lot of ground, and human sexuality gets its own treatment, most notably in the articles concerning the virtues, specifically temperance.

Temperance is a virtue by which man is able to control or govern his natural appetites. These appetites have no moral content in and of themselves, as the natural world reveals that sensible creatures (i.e., animals, etc.) have an innate inclination to fulfill certain desires, whether for nourishment, reproduction, etc. In Aquinas’ view this desire or appetite is ordered towards ‘pleasure,’ by which he means more than mere sensual gratification, but rather a gratification by which a good is pursued to one degree or another. Hence, eating is something that is both necessary for health (and therefore a good) but also something that can be a source of pleasure above the satiation of hunger. The same appetite (hunger, e.g.) is the source of both.

Human beings- being rational animals- also have this innate tendency to desire and seek sensible pleasures. However, unlike other animals, they are endowed with reason which is in some way supra-sensible. Aquinas understands the soul as the form of the body, and as such is meant to be the master of the senses. In this way, the appetites are meant to be governed by the reason, which can apprehend both the good of sensible pleasure as well as perceive good above it or evil through its misuse.

To return to the hunger example- a human being will naturally get hungry, and that instinctual drive to eat compels him to do so. The sensible appetite finds pleasure in both the satiation of hunger and in the actual taste of the food. But while some animals will eat themselves to death without realizing it, a human’s reason allows him to perceive the danger of overconsumption and avoid it, while also having the ability to both maximize the nutritional aspect and the flavorful one.

If the sensible appetites were governed completely by reason, there would be a natural balance. The reason would even at times perceive that deprivation (fasting, for example) might bring about a greater good then the satiation of hunger.

Aquinas sees sexual desires, like hunger, as part of the sensible appetite. Sexuality and its use is, like food and eating, naturally a good thing, but only when governed by reason. It is when the desires are left unbridled that sin begins to creep in.

The Sinful Bits

Aquinas understands that sin is non-being and thus has no positive content. As such, a vice or a sin is not something like a tree is a something or a person is a something, but only has its ‘being’, so to speak, in relation to a virtue. More specifically, sin can come as a result of disordered good, when things are out of proportion. Much like eating is a good until it turns to gluttony, so sexual desire is a good thing until it becomes disordered and turns to lust.

St. Aquinas treats of Lust and the Parts of Lust under the virtue of Temperance, more specifically chastity. In Question 151 he wonders aloud if Chastity is even a virtue, and if so what specific content does it have? His answer is such:

Chastity takes its name from the fact that reason “chastises” concupiscence, which, like a child, needs curbing, as the Philosopher states (Ethic. iii, 12). Now the essence of human virtue consists in being something moderated by reason, as shown above (I-II, 64, 1). Therefore it is evident that chastity is a virtue.

Concupiscence is the stand-in term he employs for the desires of the sensible appetite, usually as they try to stand over-against reason. Chastity in his view is meant to be an instructor, training the body and the appetites to restrain themselves and use themselves according to reason. Striking this balance again is the path to virtue.

Christian theologians have always faced the temptation to view all sexual desire (and even sexual acts en toto) as intrinsically disordered, for the sheer strength of sexual desire and the havoc it can wreak seem to paint it as something to be avoided at all costs.

Aquinas avoids this temptation, however, noting that:

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.

In other words, the greater a good something is, the more evil can result from its misuse. Sexual desire is a prominent example, and Aquinas points out that a great good- the reproduction and continuation of the human race- requires sexual acts to occur. However, he is quick to clarify that because this is a great good, it requires even greater care and even more application of reason, for any missteps here are going to leave things in ruins.

The Lust List

In Question 154 Aquinas delves into the various modes of lust and why they are sinful and contrary to reason, and ends up making a statement that vexes moderns to no end.

But first, the ‘parts’ of lust. Aquinas lists out six ‘species’ of lust:

  • simple fornication
  • adultery
  • incest
  • seduction
  • rape
  • the unnatural vice

Each of these has its own shades and distinctions, but he begins by asking if these things are really all that different, or if there is specific content to each and thus more or less gravity to each type of sin. He answers in the affirmative, noting that while all lust is “seeking venereal pleasure not in accordance with right reason,” there can be distinction in both the matter wherein the pleasure is sought and in the circumstances surrounding that. In his answer in Article 1 he goes on to delineate each type of list by means of these distinctions.

Simple Fornication

Aquinas approaches this article and its objections by means of a two-pronged route. He notes firstly that the end of the sexual union is to reproduce, but looks specifically at the life produced by that union. In the natural world different sorts of animals raise their young in different ways and have indeterminate unions, but in human society it is

evident that the upbringing of a human child requires not only the mother’s care for his nourishment, but much more the care of his father as guide and guardian, and under whom he progresses in goods both internal and external.

In a fascinating twist, he prefaces this observation by reminding the reader that any injury done to a human life is a mortal sin, the implication being that fornication- since it gives little regard for the well-being of the potential offspring- is in itself an assault against life, since it seeks after the pleasure of the act without allowing reason to order it towards its complete good.

However, not only is this an assault against a potential life but also an affront to human society as a whole. Aquinas takes a birds-eye view of human nature and society and realizes that we are all connected in some way. In this respect, the act of fornication is not something that can be seen as an isolated incident but one which contributes to a degradation of chastity in society as a whole. It is ultimately opposed to the good of the child, since it deprives the child of the familial structure in which he or she needs to be raised.


Like fornication, adultery does violence to the good of one’s children or future children, in that it breaks faith with one’s wife and children, and additionally harms any children that may result from the adulterous union or that already exist within the other marriage.


Aquinas was writing before the modern era in which the dangers of consaguinous unions were more widely apprehended, and thus does not make any arguments based upon potential genetic problems. However, some of his rationales lead in that direction.

He firstly notes that the bonds of blood render a natural requirement to show honor towards one’s relations, the more so the more closely related they are. The ancients tended to view the sensual viewing of the nakedness of relatives (and often even accidental glances) as something to be shunned, and thus sexual intercourse was clearly out of bounds.

Aquinas secondly points out that in the practical reality relatives have to live with each other. Given the tremendous pull of lust and the power it often has over us, if we were to regularly have sex with family members we would be even more inflamed with desire than is already the case. Such a scenario would not be ordered towards the attainment of virtue.

Lastly, he looks at the tendency of our nature to close in on itself, rather than opening itself to others. One of the beauties of marriage to those who are not closely related is that it has the potential to unite with bonds just as thick as blood those who were previously strangers. The marriage bond brings families together, and thus serves as an opportunity for the expansion of love and goodwill, whereas incestuous relationships are closed in on themselves, insular to the extreme.


Seduction is much like fornication in that it is voluntarily engaged in and no violence is offered. However, Aquinas makes the distinction in that seduction (not necessarily in the modern sense) occurs when a man seduces a woman who is still under the care and protection of her father. She willingly goes along with it, but the act destroys the good that could result from a proper marriage and, as Aquinas says, sets her down a path into a wanton life.

While this type of lust is probably absent from the modern understanding of sexuality, it is interesting to note that Aquinas ties together the good of marriage and sex into the way in which the now grown child (the daughter here) is faced with the same temptations and choices. He understands the father as responsible for providing care and protection until she enters into the good of marriage; in fact, he sees the father as responsible for ensuring that his daughter is able to attain this.

Seduction acts against this good in that it attempts to undermine both the good of marriage, the good of the family and the very act of love which compels them, merely  for the sake of lust which does not intend any of these goods.

While Aquinas’ descriptions can seem dry and sterile, he is really contrasting the fullness of love and joy and fulfillment in the end of marriage with the hollowed out nothingness that lust really is. Lust can put on the airs of love, waxing eloquently in its passion and ardor, but it is- in the final analysis- simply a fraud, for it wants only what it will take without the fullness of what love in sexuality is meant to entail. The irony is that while the desires of lust can seem so important and all-consuming, they are really pathetic leeches when seen next to the real thing.

Whereas true love and the proper use of sexuality would build up a family, provide for the good of its children and do everything to ensure they attain the happiness and fulfillment of marriage, lust can only smash and grab, leaving everything in pieces.


Many of the objections to Aquinas’ answer pertain to whether rape should really be considered a part of lust. Objection 2 is that

rape, further, implies violence… But the employment of force is accidental to lust, for this essentially regards the pleasure of intercourse. therefore, it seems that rape should not be reckoned a determinate species of lust.

Aquinas considers that while rape certainly implies violence, it is not thereby any less a part of lust. He also has a far broader concept of what is implied by ‘rape’ than more modern conceptions. For example, rape can occur when a man violates a virgin, when he steals her away from her father to marry her and violates her, and when he steals her away from her father but she consents to marry him. Aquinas (following the laws of his time) considers that any of these would be considered rape, irrespective of how the force is employed. This aspect of violence must be kept in mind to finally make sense of the final species of lust and its gravity.

The Unnatural Vice

In the final two articles on the part of Lust, Aquinas considers what he terms the ‘unnatural vice.’ This vice is labeled ‘unnatural’ in that it- as an act- is intrinsically opposed to the good of sexuality as expressed in the sexual act; that is, the propagation of children.

As an aside- this does not mean that Aquinas thinks that children are the only good of the sexual act, but rather that the potential for children is a sine qua non of its goodness. Since virtues are not opposed to each other, other goods can certainly be (and ideally will be) concomitant with the act in its proper ordering.

Since the propagation of children is, in this respect, the ‘natural’ end of the sexual act, any act which does not have that end is ‘unnatural.’ As we have seen, other parts of lust like fornication, seduction, adultery, etc., are in some sense ‘unnatural’ in that they diverge from the good of sex in various ways and according to various circumstances. But the unnatural vice is different because while adultery, for example, is disordered because it does not consider the good of the children it may produce, the unnatural vice has no inherent possibility for children at all as a part of its action.

He notes four kinds of unnatural vice: uncleanness (broadly, masturbation), bestiality, same-sex copulation and other forms of copulation that do not observe the natural manner.

Aquinas understands these as having their deformity in that they are not only contrary to right reason (like all other species of lust) but also that they are “contrary to the natural order of the venereal act as becoming to human race.” This natural order, of course, is understood to be that the natural end of sex is in procreation. Other forms of lust arise from a disordering of the concupiscence which is out of proportion from its proper end, whereas the unnatural vice has a fundamental disordering of the appetite in that it does not contain that end in its activity.

An analogy could be made with eating. The sensible appetite naturally desires to eat, and doing so involves the good of both nutrition and taste. Eating too much or eating too little are opposed to the primary end of eating (nutrition), but even in such a disordering that end still remains a potentiality.

If one were to eat with only the purpose of tasting and receiving no nutrition (say, intentionally throwing up to avoid receiving nutrition), the act of eating would be intrinsically disordered since the action is now meant only for a part of the good of eating (taste) rather than observing its fundamental and natural end (nutrition). After all, one can eat and be healthy without necessarily thinking that the food tastes good, but the good taste of food is meant to supplement the end of nutrition, not supplant it.

In a similar manner, the unnatural vice attempts to gain the good of pleasure from venereal acts but does so by supplanting the end of procreation which the pleasure of those acts is meant to accompany and in some sense inspire. As Aquinas responds:

The lustful man intends not human generation but venereal pleasures. It is possible to have this without those acts from which human generation follows: and it is that which is sought in the unnatural vice.

The Greatest Lust

Of all the vexing portions of the Summa, the article on the unnatural vice has been prone to disastrous readings and horrific misunderstandings. In modern times especially, those looking for more of a sound-byte approach to the Summa (usually intending it as a bludgeon) find ample ammunition here, for one specific reason:

Aquinas says that masturbation is a graver sin than rape.

Well, not exactly, but in the process of discussing any hot-button topic concerning human sexuality this is bound to come up, especially if one adduces arguments that broadly follow Aquinas’ approach.

The final article on the parts of Lust deals with whether or not the unnatural vice is the greatest sin among the species of lust. The wording of this article is extremely important in that the question demonstrates that Aquinas is dealing with the greatest of sins as they specifically deal with lust, abstracted from all other considerations.

Aquinas answers that the reason the unnatural vice is the gravest form of lust is that

In every genus, worst of all is the corruption of the principle on which the rest depend. Now the principles of reason are those things that are according to nature, because reason presupposes things as determined by nature, before disposing of other things according as it is fitting.

Thus, in this particular genus (lust), each species must be seen as related to the end of the venereal act, which is procreation. This principle forms the basis for determining not only how each species of lust relates to it, but also how disordered each act is in relation to that end and the other species.

The five other species of lust (fornication, adultery, incest, seduction and rape) relate to this principle and corrupt it because they are opposed to right reason and the proper ordering of the venereal act. Even though none of these intrinsically desire the actual end of the venereal act (procreation), they are nevertheless still ordered to it in some manner since that end can still obtain. This manner of corruption is still gravely sinful, but the relation to the principle is not as far removed. As Aquinas notes:

With regard to the other species of lust they imply a transgression merely of that which is determined by right reason, on the presupposition, however, of natural principles.

The unnatural vice, as already mentioned, is not only opposed to right reason but also circumvents the natural ordering of the venereal act towards its end. In the matter of the end of the venereal act, the unnatural vice is, according to Aquinas, the gravest of all.

Getting Down To It

This assertion leads many to conclude that Aquinas is stating that sexual acts like masturbation are therefore inherently worse than something like rape since rape can at least end with a child. But is this really what he is saying?

It should be noted that any understanding of Aquinas’ views on vices cannot be divorced from his understanding of virtues. Even though the virtues are not opposed to one another, that does not imply that there is not a hierarchy of virtues. Since the moral virtues are related to the reason and the ordering of the person and his appetites in various ways, there is an inherent ordering to them. Elsewhere he delineates this order as such, from greater to lesser as regards their share of reason:

Prudence (reason)
Justice (will)
Fortitude (passion)
Temperance (concupiscence)

Each virtue has its corresponding vices, and as such those vices are graver which are related to greater virtues. It should be remembered that the greater a good is, the greater potential for misuse.

Lust is opposed to the virtue of chastity, which is a species of Temperance, the ‘least’ of the virtues. And since chastity involves the ‘chastisement’ of the sexual appetite, Aquinas seems to be noting that the unnatural vice is the greatest sin against Chastity. There are other sins, of course, which are graver than this since they are opposed to a higher virtue.

But since rape is also considered a species of lust, and since Aquinas says that the unnatural vice is the gravest of the species of lust, is this all not merely hand-waving to get around him saying that masturbation is worse than rape?

Two responses are needed.

Firstly, Aquinas is coming at this primarily from the perspective of how concupiscence forms the ground of certain parts of lust. In all species of lust he understands concupiscence as the driving force behind it, overcoming the reason in one way or another. Abstracted from any other consideration, concupiscence towards venereal acts as opposed to reason desires the pleasure of the act without intending its end. In this regard the unnatural vice is graver since it more fundamentally undermines this end.

Secondly, the reason that lust is one of the cardinal sins is not because it is necessarily the worst, but rather because it is a gateway to even greater sins. So far as lust is concerned, unnatural vices like masturbation are intrinsically disordered and have a certain gravity, but other ‘lesser’ species of lust can obtain an even greater gravity because they offend other virtues.

For example, while sacrilege is not precisely a species of lust as delineated with the others, Aquinas considers that it can be if a holy object (person, in this reading) is violated by means of the misuse of the sexual act. Importantly, he makes the clarification that

the act of a virtue or vice, that is directed to the end of another virtue or vice, assumes the latter’s species: thus, theft committed for the sake of adultery, passes into the species of adultery.

In the case of lust, if it involved something pertaining to God (say, a vow of chastity), it would not only be a sin of lust but also a sin of sacrilege. There is nothing which prevents two sins belonging to the same action or which prevents a lesser sin from turning into a greater sin. This, in fact, is the sad state of our race, in that the things which seem to be not that big of a deal can suddenly explode into utter depravity.

This is precisely what is happening with the question involving whether rape is worse than masturbation and visa-versa. While in the order of lust masturbation is more opposed to the principle end of the venereal act, the sin of rape by definition involves violence, which is itself a vice opposed to justice, a higher virtue.

Aquinas explains why he thinks rape as arising from concupiscence is not as grave a violation of chastity but does grievously offend justice:

The employment of force would seem to arise from the greatness of concupiscence, the result being that a man does not fear to endanger himself by offering violence.

His point is that the concupiscent drive can be so great that it causes one to essentially lose possession of one’s reason, forgetting that to engage in certain acts so as to satisfy that desire will be an even greater evil, and in this case probably lead to severe societal consequences. The unnatural vice, on the other hand, does not necessarily lead to this sort of violence and thus has the tendency to stay at the level of offending chastity.

That doesn’t mean that it will not or cannot lead to greater sins, but Aquinas views the unnatural vice as having its fault primarily in the intentionality of supplanting reason and the natural end of the venereal act, rather than in being overcome by concupiscence.

In modern times we might be more inclined to perceive rape as arising more from a desire for dominance or power than from a desire for venereal pleasure, and in this respect Aquinas’ treatment is harder to grasp. The modern approach, however, might actually solve the apparent difficulty since the modern understanding would be more specifically about a question of justice, rather than trying to distinguish between the parts of lust.


St. Thomas Aquinas approaches sexual ethics primarily from the view that the natural end of the sexual act is procreation. This is a good not only for the copulating couple but also for the children produced and the human family as a whole. Reason is granted to humankind by which to chastise the sensible appetites, bringing them into order and proportion with the end of sexuality. Lust is a pernicious cancer towards the virtue of temperance and chastity in that inverts the order and makes the concupiscence the master of the reason, sometimes even overcoming reason altogether. Even though this pleasure is meant to be a good that accompanies the sexual act, when pursued for its own sake (and thus in a disordered manner) it can end only in disaster and ruin.

While Aquinas necessarily treats of the various sins opposed to chastity, his is ultimately a positive approach to human sexuality. When ordered properly, it allows love to blossom forth into new life and extends the care and concern which precipitated that life into the future. Ultimately, if reason and concupiscence are in harmony the good of sexuality can be provided for in the family and the society, and is the only way in which human thriving can be accomplished.

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