Where should citations be placed relative to punctuation (e.g., full stops and commas)?

In the IEEE editor's style manual it says on page 34:

References in Text: References need not be cited in the text. When they are, they appear on the line, in square brackets, inside the punctuation. Grammatically, they may be treated as if they were footnote numbers .

I would interpret "inside the punctuation" as ruling out options 1, 4, and 11, even though the grammatical treatment of footnotes is not quite clear to me.

The Springer guide does not appear to comment on the question.

Any other hints / links / viable styles?

Are you asking in general or in relation to a specific publication outlet? Are you just talking about numbered citations or are you also talking about author-name styles?

7 Answers 7

As others have mentioned, all sentences should be grammatically correct. The citation marker of the form [X] may play the role of a noun, or of silent word.

1, 4 and 11 are never correct - they put the citation into the next sentence, where it doesn't belong. Similarly, 8 and 9 put it into the wrong phrase of the sentence.

3, 6 and 9 combine words incorrectly. Spaces can't just be ignored.

That leaves 2, 5, 7 and 10. These are all used, except that the exact form of 7 will depend on the referencing style in use. You could have 'According to Smith [3]', but not 'According to Smith [Smith, 2017]', The latter would become 'According to Smith [2017]'. Also, for 10 you need to think about how long the second phrase is.

I have seen 4 and 11 at the end of paragraphs. I always took it as a signal that the whole paragraph is related to the reference and not just the immediately preceeding bit of information. Could that use be area specific? I am in engineering.

@heuamoebe I've only seen that once, and I don't like it, but it could well be area specific. My preference would be to say more explicitly at the start of the paragraph what you are doing, such as 'we recall the treatment of this topic given in [X]'.

"The citation marker of the form [X] may play the role of a noun" - [ref] is a noun? I think 'is' here would be wrong.

@VitaminE I can't quite follow your point. Mine was that you can form sentences like 'In [2] the authors prove that. '

@GuanyumingHe It varies by field. I have seen mathy sort of papers do the noun treatment more than any others.

Since you specifically mention British English, one useful style guide for academic writing is New Hart's Rules The Oxford Style Guide. I bring this book up not because it is necessarily your authoritative guide, but because the book tries to describe varied styles in use and not just the their particular in-house style, so it may give you some general idea. Of course the most relevant style guide to follow is one used by your publication venue.

In the section about author-date references, i.e. (Author 2017) or Author (2017), the guide states

The reference is placed immediately after the statement to which it relates. If this happens to be at the end of a sentence the closing parenthesis precedes the closing point (but a reference at the end of a displayed quotation follows the closing punctuation).

This should correspond to option 2 in your list if the author's name is not mentioned in open text, or a variant of 7 if the author's name is part of the sentence.

For numbered references, which I believe is more common in computer science, the guide does not specifically mention the placement, but from the examples given, brackets are placed before the full stop, like this [1]. On the other hand, a superscript number (like a footnote cue) is placed after the full stop. 2

This may depend on referencing style. According to the University of Manchester, for Vancouver-style referencing, which is very common in the UK:

If you do not mention the author’s name within your text, you should place the number in brackets at the end of the sentence, eg.

There are six distinctive conditions, which need to be satisfied, in order for a whistle-blowing case to be justified. (2)

Multiple Authors: Provide the numbers in brackets as they appear in the text after the sentence, eg.

Several drug trials proved that the antibody was released immediately. (2, 3, 9- 12)

The British Medical Journal (BMJ) likewise places the numbers after the full stop, but without brackets and in superscript, and without commas between reference numbers.

The Lancet also puts the numbers after the full stop and in superscript, with commas without spaces and without brackets. They require you to:

• Cite references in the text sequentially in the Vancouver numbering style, as a superscripted number after any punctuation mark. For example: “…as reported by Saito and colleagues.15”

• Two references are cited separated by a comma, with no space. Three or more consecutive references are given as a range with an en rule.

You need to style according to where you intend to publish, or according to your institution (e.g., for a Master's thesis or PhD thesis) or employer.

One crucial difference between people's preferences on the matter, seem to be how we interpret a citation. Is it a word or is it a mark/reference? A word should be part of the sentence. A mark/reference may mark the sentence itself and should therefore not be a part of it. A citation has the purpose of referring to further reading elsewhere, and therefore sends you off to some other text. The citation is not a word, in my opinion, unless it is a subject or object as part of the sentence. In options 5-7 the citation is an object, while in options 1-4 it is not a subject/object, but a reference marking the sentence or the last word. Citation may be treated or read as a word in some formats, like APA, but not in formats where the citation is just an index in the bibliography. Footnotes are common behind punctuation (without white space), and I think references should be treated similarly. (Some formats even use superscript for citation, just like footnotes are marked.)

Option 4, 7 and 11 (without whitespace after punctuation) are preferably. Here's my reasoning: What is intuitive and what can cause confusion?

When citing/refering to a word or expression or person in a sentence, it makes sense to refer to it immediately after. with a list of different words to cite, it is easier for the reader to follow which citation refers to which word. Citing a person would look like options 6 and 7. Choosing between them would be a matter of aesthetics. Maybe option 11 is a good choice (but without the white space after full stop), as a citation mid sentence tends to make the sentence harder to read.

To quote user1101674 in a comment on this thread:

As mentioned, they [options 1 and 11] allow for the distinction between backing the entire sentence, or just a specific part of it. So if they were commonly understood in this way (apparently they are not), they would indeed reduce ambiguity.

Using the citation as a word in a sentence looks a bit untidy. Specially if you are going for the citation format of superscript number: According to ^1, more coffee is always better. (This is option 5.)

When paraphrasing a statement (like options 1-4) it makes sense to put the citation behind the punctuation (i.e. option 1 and 4, but I would choose option 4 because it connects the citation even tighter to the sentence). This is intuitive for three reasons. First of all: You first make a statement, which should end with punctuation. Then you cite it. In my view the citation is not a word. You don't read it out loud. The citation is not part of the sentence, but refers to where the reader can read more about the sentence.

Secondly it is less confusing and more consequent and neat if there is no difference between citation location for quotes "bla bla."[XY] and paraphrases: bla bla.[XY] And don't forget if you are quoting a sentence with citation: "bla bla.[AB]"[XY]

Thirdly it would be very confusing if readers cannot distinguish a paraphrased sentence from a referred word. If the last word in a sentence is a referred word, it would look like option 2 or 3. How can you tell it apart from the case where option 2 or 3 are paraphased sentences? Does your citation regard the word "better" or the sentence "More coffee is always better."? Therefore option 2 and 3 show confusing citation sites for paraphrased sentences. We are left with option 1 and 4.

Choosing between option 1 and 4 is for me a matter of aesthetics, so I opt for option 4. Maybe someone can come up with a case where it is natural to have citation first in the sentence? If so, there may be a semantic reason for option 4 as well.

Language exists in order to understand and be understood. Therefore language and grammar ought to be designed so that confusions are avoided. That's the purpose of language.