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 corrections! [please submit sources if you send in corrections]).
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) deals with Humanity and Morals
- Part III (Tertia Pars) deals with Christ
Each Part is composed of Questions:
- Part I has 119 Questions
- Part II is divided into two parts:
- The First Part of Part II has 114 Questions
- The Second Part of Part II has 189 Questions
- Part III has 99 Questions
Each Question is dealt with in Articles made up of five sections:
- The issue of the article is given in the form a question.
- Several plausible responses are listed.
- A contrary response (reflecting Thomas’s thinking) from some authority is cited (the sed contra – “On the contrary”).
- Arguments are given for Thomas’s response (the respondeo – “I answer that”).
- Brief replies are given to objections based on the initial responses (the adversus – “Objections”).
When citing passages from the Summa, do not use page numbers.Standard notation procedure is to list the above elements in a consistent manner . . . However, convention varies widely (see examples from scholarly sources below). So check with your school / professor for preferences, and 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
- If it is a Reply to an objection, abbreviate adversus as “ad” followed by its number
Examples:
- Sum I-II, 2, ii, ad. 1.
- ST I-II, Q. 3, Art. 2, ad. 1.
- ST I-II, Q 3, A 2, ad. 1.
- S.T. I-II, 2, ii, a.1.
- Ia.22.2
- Ia.I: 19, 34, 193(53)
- Ia. 3, 2 ad 3.
- 2a2ae. 180, 10. 3a 35, 8.
Other Considerations:
- * The title of Aquinas’s work is Summa Theologiæ (Lt. for “Summary of Theology”), but it is sometimes titled Summa Theologica (e.g., NewAdvent.com and the popular Benziger Brothers 1947 translation). If you are not referencing a translation with “Theologica” in the title, stick with Summa Theologiæ.
- 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”).
- **Aquinas never finished the Summa, but there is a Supplement compiled from his work on the Sentences attached to part three.
- 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.
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).
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!
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. 
I think you should have used the cake picture.
Nice!
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Thanks for the easy guide.
What if you are citing that which comes before the articles? (what we would usually call “preface”) How would you reference this?
For example, Aquinas will say “We next consider those things that pertain absolutely to the will of God” etc. (e.g. ST I, Q. 20). How should this be cited?
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.
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.
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.
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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part 3 has 99 questions
Ooops! Thanks! S9metimes I cann9t type very well.
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.
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?
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.
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.
20 paras in one article?… Not anywhere I’ve been lately.
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!
I do what I can.
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?
It should mean: Summa Theologiae, Second Part of the Second part, question 66 article 8 and question 188 article 3.
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.