When you have multiple sources for information like a quote, which source do you use in your book or essay. The one you may have gotten from an authors work about what a particular individual said or do you cite this persons original work?

For example I have this passage in a book I'm reading.

Thomas Aquinas (d. 1274) believed that intercourse with a pregnant woman was a mortal sin only when there was a danger of miscarriage (Commentary on the Sentences 4, 31, 2, 3)

If in my essay or book I wanted to say that Aquinas believed intercourse with a pregnant woman was sinful, do I cite the author's work above for my source or find exactly what Aquinas said in Commentary on the Sentences and cite that?

5 Answers 5


As others have noted, you cite the source that you actually used. If A quotes or describes B, and you have read A but have not read B (whether because it's not available, you just didn't bother, or whatever), then you cite A.

It is generally considered better to go to original sources. If some later writer says that Aquinas said sex with a pregnant woman is a sin -- and let me interject here that I have no idea what Aquinas said on the subject, I've read pieces of the Summa but I've skipped many pieces too -- the later writer may be misquoting Aquinas or applying his own interpretation to something ambiguous. If you were to say, "Aquinas said X" because some other writer claims he said X, that would simply be wrong. Especially if the writer did not give the exact quote, but even with an exact quote, you could be missing the context.

So if your point is to say, "this is what Aquinas" said, you should go to the source and read and quote (and cite) Aquinas. It's easy enough to get copies of Aquinas on the web these days. If your point is to say, "this is how so-and-so interprets Aquinas", than you should quote (and cite) so-and-so.

Some writers will give a citation like, "Aquinas, as quoted in ...". This is a reasonable thing to do if the original source is difficult to obtain. Like if he's quoting a book that is no longer in print and you can't find a copy. It's most clearly valid if the original book no longer exists, like if you're quoting a book written in AD 300 that quotes an earlier book and that earlier book has been lost to history. But for something easily available like Aquinas, for a scholarly paper I'd just get the original.


You cite the (or a) source that you used. If you read it in Book A and that book says it came from Book B, you cite Book A because that's your source. If you choose to follow the reference and see it in Book B yourself, then you could cite either A or B (you used both). In that kind of situation, it's generally best to cite the source that's closest to the source -- why cite A who cites B if you can cite B directly?

Why shouldn't you cite B if you read it in A and you think A is reliable? Well, partly because sometimes sources get it wrong -- B might not really say what A says it does. But, more broadly, any author who's found to do this sort of thing -- citing a source that he didn't actually verify directly -- calls into question all of his citations. If you think A is reliable then either (a) your readers probably do too, so citing A means something, or (b) you can explain why A is reliable.

  • "Why shouldn't you cite B if you read it in A" ...because citations should refer to the source of given quote to allow finding a broader context, especially if the quote is not representative of the "middleman" work, only discussed, and it's not the "middleman" who was the author of that quote. If you quote Thomas Aquinas, you shouldn't attribute the quote to "Professor Diabolicus, Cruel Christianity", you should attribute it to Thomas Aquinas, and the work from which "Cruel Christianity" took the quote you're repeating...
    – SF.
    Apr 21, 2015 at 11:22
  • @SF. only if I chased the reference; otherwise, for all I know, Professor Diabolicus got the quote wrong or intentionally warped it. If I'm going to rely on the secondary source then the way to attribute it is "according to [Diabolicus], Thomas Aquinas said....". But I should really be skeptical of my secondary source and go see for myself -- and then cite Aquinas directly. (Well, presumably somebody's translation, but you get the idea.) Apr 21, 2015 at 13:04
  • This all crashes on "Well, presumably somebody's translation" - as long as you're not quoting the original source but some derivative like a translation, you've already broken the direct bond; the translator could have made exactly the same mistakes or changes.
    – SF.
    Apr 24, 2015 at 9:15
  • @SF. yes, which is why if you use a translation you need to cite it. "Aquinas said X" -- no, not unless you read those words yourself. "Aquinas said X (So-and-so's translation)", yes. We see this with biblical citations all the time -- "Leviticus says X" when you pulled it out of some translation with either an agenda or a lack of rigor and that's not what the Hebrew actually says. Far better to say "Leviticus says X (KJV)" or whatever. Apr 24, 2015 at 13:04

Both the MLA Handbook and the APA Manual state that in academic writing you must have read what you cite. Since you cannot have read a source of which you know only a short passage quoted in another text, you must get the original, read it, and cite that.

The reason is that any citation might misrepresent the original or withhold relevant information or that you might come to completely different conclusions than the secondary author.

You may cite from a secondary source only if it was not possible for you to get hold of the original source, which, in this time of online publications, interlibrary loan and digitized texts, is a rare occurrence and needs to be explained in text.

Not having enough time to read all the relevant literature is no excuse. When you do research you must read everything, otherwise your research will be irrelevant. If you are not doing research and cannot read everything, then you must not quote what you haven't read.


Reference the quotes AND associated conclusions to respective authors.

You have two options in this case:

  • silently agree with the author of "Commentary..." and express their opinion as your own, supporting it with quote from Thomas Aquinas, and restrict your credit to relevant parts in the original "Sentences" - likely as sourced in the "Commentary". This way you used "Commentary" only as a learning resource that aided you in finding the respective source and aided you in forming your own opinion. You don't quote it, you quote Thomas Aquinus and express your own conclusions which happen to be similar to "Commentary" ones - you state "Aquinas believed intercourse with a pregnant woman was sinful"

  • refer opinion stated in the Commentary and present your own position in regard of that. Provide a quote from "Commentary..." and credit it with relevant references *to the "Commentary...". Include the full framing of the quote including opinion of the "Commentary" author and then express your opinion on that: "The author of 'Commentary on the Sentences' believes Aquinas believed intercourse with a pregnant woman was sinful. Considering the quotes presented from the original Sentences I'm inclined to agree with that conclusion."

It's up to you to choose the right option. If the quoted Sentences unambiguously support your thesis, go with (1) for clear, strong impact. If the quote is not so obvious, paraphrased, explained in finer details, referred etc, go with (2).

In the specific case you presented I don't see a single word directly quoted from Aquinas; this would mean you aren't referencing or quoting the source material - you are following the analysis, so (2) is the correct choice.


Always cite the original work, even if you have to spend time finding the details like the publisher and the year. You must give the original source the credit. Only use a secondary source if you need to criticise the use of the quote.

Using secondary sources can lead to tralatitious activity.

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