What is sex/gender, according to St Thomas Aquinas?

“Come, Holy Spirit, Divine Creator, true source of light and fountain of wisdom! Pour forth your brilliance upon my dense intellect, dissipate the darkness which covers me, that of sin and of ignorance. Grant me a penetrating mind to understand, a retentive memory, method and ease in learning, the lucidity to comprehend, and abundant grace in expressing myself. Guide the beginning of my work, direct its progress, and bring it to successful completion. This I ask through Jesus Christ, true God and true man, living and reigning with You and the Father, forever and ever. Amen.” — A Student’s Prayer (by St Thomas Aquinas)

I recently submitted this primary text analysis to my university. Feedback from my assessor are in italics and brackets:


For the most part, the answer to this question can be found in De Ente et Essentia, para 99 onwards.[1] Not only is essence found in all substances, but it is also found in accidents. An essence is understood by how it is defined, and this applies to the essence of an accident as well. However, an accident’s essence’s existence is not separate from its subject, much like hylomorphism — such existence is a substantial act. Both accident and its subject gives rise to an accidental act of existence.

Therefore a substantial form’s essence is incomplete, because the form’s definition has to include the form itself, and be framed outside of its genus as well, much like the accidental form’s definition. For example, if the soul is the form of the body, then the body would also be included in the definition of the soul. The soul has powers and accidents, and of the two, it is the soul’s powers that cannot be withdrawn, as an accident can be present or absent without corrupting the soul.[2]

To clarify, the difference between substantial and accidental forms, is that a substantial form’s existence is not separated from that which it informs, namely, matter.[3] This hylomorphism is an act of subsisting existence that yields a certain essence, and where the form, an incomplete essence, is part of a complete essence anyway. On the contrary, that which is informed by an accident is in itself a complete being, a subsisting existence which precedes the supervening accident. As such, the accident and its subject is not a composite, because the accident is coincidental. Here, the accident and that which it informs together does not give rise to a hylomorphic essence, so for this reason an accident is neither a complete essence nor a part of a complete essence.

(But in the first paragraph you said that “an accidental essence’s existence is not separate from its subject”. Perhaps you meant to use the words “preceded by” instead of “separated from”? Because you are about to make the point that substances precede accidents, to which you could add that prime matter does not precede the substantial form to which it is united.)

That substance which is the first kind of its genus at the most fundamental level is the cause of accidents, thereby rendering an accident as a being with some qualification, and an essence with some qualification. Therefore, a substance is made up of matter, form, and accident/s primarily derived from form. But there are accidents that derive from matter which only exists through form (examples needed), and there are certain forms, like the intellect, whose existence is not matter-dependent. Here, intellect takes place outside of the human body, because form-derived accidents can be found in all individuals of the same genus, like risibility.[4]

On the other hand, sensing communicates with matter, and is derived from the form (Do you mean sight is a form or something else?), but either way, an accident does not derive from matter without communicating with the form. Some matter-derived accidents relate to the specific form. For example, there are animals who are male and animals who are female. If the forms of these animals were to be disembodied, these male/female accidents would not exist. This can be contrasted to other matter-derived accidents which relate to the generic form, where once the form is disembodied, the accident/s remain in the matter, such as skin colour which is derived from the elements and not from the soul, and therefore remains after death.

Matter-derived accidents are accidents of the individual, where they differ to other individuals of the same species. (Good, a definition! This could have been stated earlier to avoid confusion.) In this sense, the concrete names of accidents, such as ‘fur-coated animal’ could not be categorised under a species, unless the accident is a species itself, such as fur-coatedness. But if accidents are not hylomorphic, their species would be their mode of existence, such as quantity or quality. (This could be expressed more clearly. What precisely do you mean by “hylomorphic” in this context?) Therefore, there is sufficient, though convoluted, evidence to suggest that Aquinas understands sex/gender to be an inseparable accident derived more from matter than from form.[5]

(Are you saying that these words are synonyms in Aquinas’ understanding? If so, you need to justify this interpretation. Or if you think that he believes that sex and gender are distinct concepts, then you may need to refer to the Latin to justify your translation.)

Critical Evaluation

Matter, being the factor overriding form on the question of sex/gender, matters more so when consideration is given to Aquinas’ Summa Contra Gentiles. Here, Aquinas disputes the argument that the embryo’s vital operations before complete development proceed from the mother’s soul on the basis of body-soul composition.[6] He further disputed the argument that the semen comes into being as a soul, as a complete essence, because the semen is only a potential soul — substantial form does not precede substantial generation.[7] Therefore, in the case of male masturbation, rational souls do not multiply from the man,[8] rather, the progressive reforming of the embryo over time is due to a formative power acting on the generative soul of the father.[9]

Since Aquinas understands sex/gender in terms of how man and woman uniquely generates human offspring, that is, sperm and ova production respectively, sex/gender is derived from matter only if matter, and not the substantial and accidental forms of the soul, is the only factor in determining the male or female role the human person plays in generation. Whilst form plays a role in the sense that a potency does not become an act without form, Contra Gentiles does not clarify whether it is matter or form that ultimately determines the sex/gender generative role the human person plays.[10]

However, Contra Gentiles is based on Aquinas’ outdated understanding of biology. Aquinas argued that God created woman to generatively help man, since some living substances do not self-generate, but are generated by some seed or non-seed-giving other. That is, man is the perfect animal when he is actively and generatively male, since intellect is found in the original human person, man, leaving the female human person, a complementary but defective helper.[11] If the material seed’s generative destination determines sex/gender, sex/gender is therefore derived from matter, not form.

(Aquinas says in the reply to objection 1 that “as regards human nature in general, woman is not misbegotten…” Woman is “defective and misbegotten” “as regards the individual nature”. Aquinas did not know about how sperm carry either X or Y chromosomes. So, considering that all sperm are somewhat the same, and that they are the active force in generation, in perfect circumstances the active force would replicate itself, creating a likeness of itself. Something has to intervene (Aquinas mentions a cool south wind!) to cause the production of a woman. So in this sense Aquinas sees the individual generation of a woman as a defect, since it is a deviation of sorts from the norm. Faulty biology, but I think the word “defective” is unhelpful and leads to misunderstanding.)

But according to Summa Theologiae, the intellectual and will-driven operations of the soul do not require the body, where the powers of intellect and will are in the soul as their subject. Other formal operations do however, require a body, such as sightseeing, much like vegetative and sensitive souls.[12] Therefore, such operative powers have their subject in the body-soul composite, rather than in the soul.[13] So if a subject of operative power has accidents which denominate its proper subject, sex/gender would be of the substance, wholly. Since this does not clarify whether it is matter or form that ultimately determines sex/gender, the position contrary to Summa Theologiae in this matter merits scrutiny.

The contrary position in question is that sex/gender is derived from the substantial or accidental form of the soul. If this was true, boys/men would be a species different to girls/women as a species, because it is the substantial form that determines the species. Further, if intellect and will is what differentiates rational from sensitive animals, the addition of a sexed/gendered generative power to the human soul, in accidental form, would indicate two different types of rational soul based on sex/gender. This, again, would imply there are two species based on sex/gender.[14]

In conclusion, an individual matter and its accidents is not by definition, a genus. For example, the form of humanity and the human person is not the same thing.[15] Therefore, according to Aquinas, sex/gender is an inseparable accident derived from matter, not form.

(This is a strong paper Dana. You have unpacked some dense Thomist terminology in order to analyse contemporary concepts of sex and gender. Your summary of Aquinas’ argument in part 1 was quite good, although some direct quotes would strengthen your interpretation. A clear definition of “matter-derived accidents” was eventually stated, but could have come when you first talked about matter-derived accidents. Further, it was not clear whether Aquinas would understand “sex” and “gender” to be synonymous, or whether there are grounds to argue for a distinction in his thought.

Your writing style is succinct, which is a strength. On occasions you jump too quickly from one idea to the next. Lead your reader gently from sentence to sentence. The paper would also have been strengthened by more substantial engagement with secondary literature. You have only two items here (Newton & Finley). At the postgraduate level and for a paper of this length, we would be looking ideally for about 10. Some of the texts and issues here are contested by different interpretations, and a clearer sense of this debate would elevate your argument.)

Related Formative Assessment: Student Forum

Student X: If Thomas Aquinas says that the soul is a kind of mover that is moved accidentally, what would be the mover of the soul?

Dana Pham’s response to Student X: The mover of the soul would be the unmoved Mover, that is, God, from a Thomistic point of view. It is the first of Aquinas’ Five Ways. What a being becomes is still the same being because of the ‘back and forth’ relationship between act and potency. Such movements cannot self-occur, and that requires an unmoved Mover that is all act, has no potency, but is responsible for the potency of all other beings. This is probably one of the most significant philosophical concepts that allowed Aquinas to Aristotelianise Christianity. It also complements the Thomistic argument that the soul is the substantial form of the body.

Student Y: The confusion between Cartesian Dualism and Thomist metaphysics of mind is that Descartes says the soul is the separate mover of the body, whereas Aquinas says that the soul is the form of the body and has the immaterial power of the intellect which is the form of the soul itself. The key differences here are that Aquinas says that the soul is subsistent and composed of soul and matter which individuates the person, and that Descartes saw the soul as the person himself/herself, without need for a body, like an angel. Descartes here takes after Plato while Aquinas definitely takes after Aristotle. Also, with Descartes, the intellectual soul is already individuated before interfacing with the body given to it at conception whereas Aquinas goes with Aristotle in saying that the human soul is individuated through matter, so through the potential of the human form to manifest genetically, through biochemistry, and hence through base elements. The issue is how does an immaterial intellect operating through the subsistent soul individuate at all beside its own personal individuation as in Descartes?

Dana Pham’s response to Student Y: I do not believe that the intellect is strictly immaterial. Thomistically, the soul is the substantial form of the body, therefore the soul is a substance, and could not be immaterial. On this basis, if the intellect comes from the substantial form that is the soul, it then appears that the intellect individuates as that of the body-soul composite, that individuates. Because of the human person’s composite state, the intellect individuates as an act-potency phenomenon integrally with the rest of the human person. As Aquinas argued, the human person “is one and the same man who is conscious both that he understands and that he senses. But one cannot sense without a body: therefore, the body must be some part of man”.

(Great job on this assessment, Dana. Your questions on the Google Doc discussion were clear and pertinent, which caused many students to pick up on them and attempt replies. Your reply to the first question draws on some key concepts in Aquinas and deals with the question satisfactorily.

The second reply is reasoned and mostly clear. Aquinas does seem to believe that the intellectual power is immaterial, even though the body is an essential part of our essence. It is not a contradiction to say that the soul considered in itself is immaterial (or the immaterial principle) while the person, who is body and soul, is a material being (informed material and immaterial principles).)


Aquinas, Thomas. Contra Gentiles. trans. James F Anderson. New York: Hanover House, 1955–57.

Aquinas, Thomas. De Ente et Essentia. trans. Joseph Kenny OP. St Thomas Aquinas’ Works in English website. 1965. https://isidore.co/aquinas/english/DeEnte&Essentia.htm.

Aquinas, Thomas. Quaestiones Disputatae de Anima. trans. John Patrick Rowan. St Louis and London: B Herder Book Co, 1949.

Aquinas, Thomas. Summa theologica. trans. Fathers of the English Dominican Province. New York: Benziger Brothers, 1911–25.

Finley, John. “The Metaphysics of Gender: A Thomistic Approach.” The Thomist 79, no. 4 (2015): 585–614.

Klima, Gyula, Allhoff, Fritz, and Jayprakash Vaidya, Anand. Medieval Philosophy: Essential Readings with Commentary, 1st ed. Chichester: John Wiley and Sons (UK), 2007.

Newton, William. “Why Aquinas’s Metaphysics of Gender Is Fundamentally Correct: A Response to John Finley.” The Linacre Quarterly 87, no. 2 (2020): 198–205.

[1] Thomas Aquinas, De Ente et Essentia, trans. Joseph Kenny OP, St Thomas Aquinas’ Works in English website, 1965, https://isidore.co/aquinas/english/DeEnte&Essentia.htm.

[2] Thomas Aquinas, Quaestiones Disputatae de Anima, trans. John Patrick Rowan (St Louis and London: B Herder Book Co, 1949), a.12 ad. 7.

[3] Gyula Klima, Fritz Allhoff, and Anand Jayprakash Vaidya, Medieval Philosophy: Essential Readings with Commentary, 1st ed. (Chichester: John Wiley and Sons (UK), 2007), 245.

[4] Klima, Allhoff, and Vaidya, Medieval Philosophy, 247.

[5] Klima, Allhoff, and Vaidya, Medieval Philosophy, 247–48.

[6] Thomas Aquinas, Contra Gentiles, trans. James F Anderson (New York: Hanover House, 1955–57), IIa, ch. 89, para. 2.

[7] Aquinas, Contra Gentiles, IIa, ch. 89, para. 3–4.

[8] Aquinas, Contra Gentiles, IIa, ch. 89, para. 5.

[9] Aquinas, Contra Gentiles, IIa, ch. 89, para. 8–11.

[10] William Newton, “Why Aquinas’s Metaphysics of Gender Is Fundamentally Correct: A Response to John Finley,” The Linacre Quarterly 87, no. 2 (2020): 199.

[11] Thomas Aquinas, Summa theologica, trans. Fathers of the English Dominican Province (New York: Benziger Brothers, 1911–1925), Ia, q. 92, a. 1.

[12] Aquinas, Summa theologica, Ia, q. 77, a. 5.

[13] John Finley, “The Metaphysics of Gender: A Thomistic Approach,” The Thomist 79, no. 4 (2015): 598.

[14] Newton, “Why Aquinas’s Metaphysics of Gender Is Fundamentally Correct,” 199.

[15] Aquinas, Summa theologica, Ia, q. 3, a. 3.



Get the Medium app

A button that says 'Download on the App Store', and if clicked it will lead you to the iOS App store
A button that says 'Get it on, Google Play', and if clicked it will lead you to the Google Play store