Citing the Summa Theologiæ of St. Thomas Aquinas

Having struggled with this issue for some time, I thought I would attempt to get a final answer as to how Thomas Aquinas’s Summa Theologiæ* is to be cited in academic writing. What I discovered is that there seems to be no authoritative answer. This does not mean, however, that there are no wrong ways to do so. Below I present my findings (all subject to change as Thomists from around the blogosphere send in suggestions!).

Citing the Summa is based on its structure, so let’s begin with that.

The Summa has three main divisions called Parts:

  • Part I (Prima Pars) deals with God
  • Part II (Prima / Secunda Secundæ) is in two parts dealing with Humanity and Morality
  • Part III (Tertia Pars) deals with Christ

Each Part is composed of Questions:

  • Part I has 119 Questions
  • Part II has 303 Questions total:
    • The First Part of Part II has 114 Questions
    • The Second Part of Part II has 189 Questions
  • Part III has 99 Questions

Questions are dealt with in Articles, each made up of five sections:

  • The topic of the article is given in the form a question.
  • Plausible responses are listed as Objections (the adversus).
  • A contrary response (reflecting Thomas’s thinking) from some authority is cited (indicated by sed contra – “On the contrary”).
  • Thomas argues for his response [the respondeo – “I answer that” (aka corpus)].
  • Brief replies are given to the initial objections.

When citing passages from the Summa, do not use page numbers (this would be like saying “Bible, p. 232”). Proper notation procedure is to list the above elements in a consistent manner; however, conventions vary widely (see academic examples below). So check with your school / professor for preferences, then just be consistent.

  • Part Number
    • First Part: “I” or “Ia”
    • First Part of Second Part: “I-II”  or “Ia-IIæ”
    • Second Part of the Second Part: “II-II” or “IIa-IIæ”
    • Third Part: “III” or “IIIa”
    • **Supplement: “Suppl.” or “Suppl. IIIae”
  • Question Number
  • Article Number
    • For a Reply to an objection, abbreviate adversus as “ad” followed by its number.

For those wanting to cite the prologue to a question or the subsections of an article within a question, the Latin text uses the following abbreviations:

  • pr. — prologue to a question
  • arg. — objections
  • s. c. — “On the contrary”
  • co. — “I respond that”
  • ad. — replies to objections

Various Academic Citation Examples:

Other Considerations:

  • Although it is allowable to simply use “ae”, to make the “æ” character, in MS Word use character code 00E6 under INSERT, or, to make it in HTML type “æ” where “ae” would have gone (e.g., “Summa Theologiæ”).
  • Thomas’s “last name” derives from his family’s place of origin in Aquino, Italy – so, Thomas of Aquino. Thus, his name is rendered Thomas D’Aquino in Italian (Thomæ Aquinatis in Latin means “of Thomas Aquinas”). For an English source citation or bibliography entry, his name is typically listed as “Aquinas, Thomas.” (Thanks to Prof. R. Howe for this insight!)
  • Full bibliographic information on the Summa should only be included in its first citation and in the bibliography. After that, just use standard notation.

* The title of Aquinas’s work is Summa Theologiæ (Lt. for “Summary of Theology”), but it is sometimes titled Summa Theologica (e.g., and the popular Benziger Brothers 1947 translation). If you are not referencing a translation with “Theologica” in the title, stick with Summa Theologiæ.

**Aquinas never finished the Summa, but there is a Supplement compiled from his work on the Sentences attached to part three.


47 thoughts on “Citing the Summa Theologiæ of St. Thomas Aquinas

  1. A couple of minor points. Actually, Thomas was not from Aquino. Rather, he was born in Roccasecca, about 7 miles from Aquino. (I’ve actually been to both Roccasecca and Aquino, so that obviously makes me an expert!) As such, (as I understand the data) his last name actually was “Aquinas.” It is true that the name ‘Aquinas’ came from the city from where his family came, by the time Thomas was born, this had become the family name. It would have been his ancestors (parents or before) who were “_____ of Aquino. See, James A. Weisheipl, Friar Thomas D’Aquino: His Life, Thought, and Works with Corrigenda and Addenda (Washington, DC: The Catholic University of America Press, 1983); Jean-Pierre Torrell, Saint Thomas Aquinas, 2 vols., vol. 1 The Person and His Work, and vol. 2 Spiritual Master, trans. Robert Royal (Washington, DC: The Catholic University of America Press, 1996); M.–D. Chenu, Toward Understanding Saint Thomas, trans. A.–M. Landry and D. Hughes. (Chicago: Henry Regnery, 1964).

  2. Oh, I forgot to say, but your citation information is tremendous! Thanks so much. As you know, this has been something that I’ve never been clear on (even after having done a Ph.D. dissertation on Aquinas!). Good work!

  3. Thanks Richard! Your vast travels are just one reason why I included you on the original edition email. 🙂 I have amended my previous statements, giving you full credit [i.e., “blame” should you be incorrect] of course. 🙂

  4. Good question! I would just cite the section it is in to the lowest level you can. So if you are in the segue between articles, cite to the question. Since there is no official way to cite the Summa, you could just add “Prologue” or something to the end of the citation to be more clear – but none of his sections are very long so they should be fairly easy to find if you just cite one level higher.

  5. Thanks so much for a very clear explanation. I’m editing a dreadful translation from Spanish that uses what seems to be made-up or Spanish conventions, and had no idea how to render them into a format used in U.S. English texts.

  6. Excellent post! Just a couple minor corrections. (1) You write, “his name is rendered Thomas D’Aquino in Italian, and Thomæ Aquinatis in Latin.” However, in Latin his first name is “Thomas”; the form “Thomae” is the genitive and dative of his name. (2) The character æ is not a letter; it’s a ligature of two letters. Therefore it is completely proper to write it as “ae”. You see the same principle at work in the lower-case letter A: some fonts write this as a small loop with a bar curved at the top, and some fonts write this as a large loop with a straight bar. When an author quotes a source, he or she does not have to make the font of these A’s match the original! In just the same way, some typesetters write “ae” as a single ligature (æ) and others as two ligatures (ae), but you don’t have to imitate them.

  7. Fantastic! Thank you, I will incorporate your comments into the post (and then probably delete it so it looks like I came up with it in the first place hahaha – just kidding). Thank you very much.

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  9. How would you cite the “respondeo” specifically?
    Like this: ST, III, 10, i, resp.
    Or would you simply leave out the “resp” and quote the entire article?
    Thanks! This is a great resource here.

  10. Hey David, thanks. I’d add “resp.” – but it is a matter of preference, I suppose. The way I see it, it is only accidental that a given article may be short enough for someone to locate a quote efficiently if only the article is cited – and since we have such a nice organization system in place, why not use it? 🙂

  11. My paper partner quoted “q91, a2, p.20”. What’s the “p” for? Pleeease tell me. I can’t ask my partner. She’s a chic I want to impress. 🙂

  12. No “p.” designation that I am aware of. She might mean paragraph if there is more than one in a given section or she might be making a newbie mistake and citing the page. 🙂

  13. Not really. The parts that we quoted were quite short. It’s fine, though. Our paper’s done and I followed you! Ha ha. Although I don’t think she was impressed enough for her to dump her boyfriend for me. Lol! Thanks, Doug!

  14. Great explanation and very clear, however a book I am reading cites ST like this: 2a, 2ae, q. 66, a. 8 and 188, a 3. What am I supposed to make of that?

  15. Thank you, that was very timely and helpful. It also made me realize I needed a hyperlinked table of contents, kindle edition of the ST. Found what I was looking for right away.

  16. Hi Doug,

    I work at a company that produces audiobooks. I’m researching terms for a particular book that references Summa Theologica. Can you help with the following two citations?

    ST 3.22 a4r
    ST 3.83 a6 ad3 ad7

    How exactly should they be read aloud?

    For example, would the first citation read as: “Summa Theologica, third part, question 22, article 4…”

    My biggest question is how to reference the lowercase “r” and “ad.”

    I have the full ST text in front of me and along with your tutorial I have made (poorly) educated guesses, but I’d love to have your feedback. Thank you so much!

  17. Interesting question – one I will gladly answer for the free copy I will surely receive when you’re done. 🙂

    Since it is an audio book in English, I would translate as much of the citations as possible into English. This should present no problems with the main structural indicators: “Part,” “Question,” “Article,” etc. plus the number, for these are probably already shown as headings in your copy. The difficulty with the other references you asked about is that they refer to the “subsections” (which are sometimes just a sentence) within an article that do not get headings.

    These “subsections” are sometimes referred to by the first word or words typically used in the sentence or paragraph. The “Sed Contra” for example means (and is usually translated) “On the contrary” and is where Aquinas gives a contrary position or quote to those he opened with. Or Aquinas’s response “respondeo dicendum quod” (“r”) is usually translated as “I answer that.” “Ad” is a preposition usually meaning “to” as in “to this.” Etc. If you have citations that utilize these sub-section references, you could either say the Latin “name” to which the abbreviation refers (“r” = “respondio”) or translate the word(s) the abbreviation refers to (“r” = “response”).

    Personally, I think you should be consistent: all English or all Latin. If you’re going to say “Part One” instead of “Prima Pars,” or “Article” instead of “Articulus,” then don’t mix it up by going back to Latin later. I also would not just say the letters of the abbreviation since they are actually Latin abbreviations (that are not well known, unlike “etc.”). Just as you would not say “S T,” for Summa Theologiae (which is pronounced tay-oh, btw) “P,” for Part etc., also do not just say “r”.

  18. Thank you Doug. VERY helpful. The book is Why Priests? A Failed Tradition by Garry Wills. The audio version will be available later this year via the National Library Service for the Blind and Physically Handicapped (NLS).

  19. For those wanting to cite the prologue to a question or the subsections of an article within a question, it may be helpful to know that the Latin text available on uses the following abbreviations:

    pr. — prologue to a question
    arg. — objections
    s. c. — “On the contrary”
    co. — “I respond that”
    ad. — replies to objections

  20. My professor believes it is silly that the first and second parts of the second part are cited 1-2 and 2-2 (or rather 1a-2ae and 2a-2ae). He thinks it is more logical that it should be cited as 2-1 and 2-2 (2ae-1a and 2ae-2a) but I have not seen it cited like this anywhere else. Is my professor wrong? Or is it permissible to cite it in this way?

    Not that it is important but I’m also wondering whether the fact that I am studying in South Korea (so maybe some sort of cultural difference) is a reason why.

  21. Haha, yes it is somewhat confusing even in the West. The numbers reflect the titles, though – not so much a numerical outline. The actual title is “first / second part of the second part” so if you remember that it is a bit easier.

  22. What would the “co.” stand for, given the Latin opening to the “I respond/answer” section is “respondeo”? I see that’s the standard abbreviation at the corpusthomisticum site referenced, just don’t know what it stands for.

  23. Chuck B. – Excellent question! Even the internet did not seem to know this one. According to my sources (Brandon Dahm), it stands for “corpus” – I suppose because it forms the “body” of Aquinas’s position. I am not sure why that section is not just called that though! I will add this info into the main post and maybe next time google will know the answer. 🙂

  24. I put together some guidance for citing the Summa in the “instructions for contributors” for a theological journal I help to edit. Here it is, for what it’s worth (if this is in error in some way, I’d appreciate knowing about it!) (Italics aren’t coming through for this item, but “Summa,” “Summa Theologica,” and “ST,” as well as the Latin phrases “sed contra,” “respondeo,” and “adversus” should all be italicized):


    Format for the citation of the Summa Theologica of Thomas Aquinas (if the Summa is being quoted, full bibliographic information should be given for the edition being quoted):

    Thomas Aquinas, Summa Theologica, I.13.1 co. Aquinas, ST II-II.8.7

    Explanation: (1) The initial roman numeral stands for the “Part” of the Summa (I, II-I, II-II, III). Note carefully that some citations of the Part give Latin suffixes to them, e.g., Ia (“prima”), IIa-IIae (“secunda secundae”). These are suffixes, not subparts, and can be safely omitted. (2) The first arabic numeral stands for the “Question,” which is the next level down from the “Part.” (3) The third arabic numeral stands for the “Article,” which is the next level down from the “Question.” (4) An “Article” has a standard format of five parts: the issue is given in the form of a question, several plausible responses are given, a contrary response from Thomas is provided from some authority, arguments are provided for Thomas’s response, and brief replies are given for objections based on the original responses. Because an Article can be rather lengthy, a citation might specify which section of the Article is being referred to. This is done with Latin abbreviations: pr. (prologue to the question); arg. (objections); s.c. (sed contra, on the contrary); co. (the respondeo, I answer/respond); ad. (adversus, replies to objections).

    Example: ST I.13.1 co. indicates the “I respond” section of Part I, Question 13, Article 1 of the Summa.

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