# Double parenthesis in academic writing [duplicate]

I have the following question. I have a text in which I want to insert a small mathematical formulation, namely between parenthesis. Unfortunately, this mathematical formulation also contains a parenthesis, which would result in a double parenthesis in the text. Is this allowed in academic writing or do I have to formulate it differently? My text looks like this, for example.

This leads to a function (f(x)), which then...

• Why would you put the mathematical expression in brackets? Apr 21 at 7:17
• Assuming there's a good reason to put the function in brackets in the first place, I'd say there's nothing wrong with the double closing )). In the particular example cited though, where there's already a comma, maybe just use another one in front, thus: This leads to a function, f(x), which then... Apr 21 at 7:30
• @user95861 This is good advice, but write that as an answer, not as a comment! Apr 21 at 8:38
• Putting the general question about double parenthesis aside for this case: Why not just write: “This leads to a function f, which …”? First, f(x) almost certainly is a value, not a function (unless f is a function-valued function). Second, the outer parenthesis seems unnecessary. Apr 21 at 18:55
• Frankly, just to anything that looks good and feels right to you and your coauthors, and count on the copy editing process to make your manuscript conform to a journal's style sheet. Try not to sweat the small stuff. The only caveat is to carefully read the Instructions to Authors. Apr 22 at 18:36

Is this allowed in academic writing or do I have to formulate it differently?

There is no Central Committee for Academic Writing issuing decisions on which things are Allowed and which are Not Allowed, so it does not make a lot of sense to formulate the question this way. There are just people with various opinions on what constitutes good writing, with near consensus on some things and violent disagreement on others. So it is really up to you to figure out which principles you want to follow when it comes to parentheses etc.

Accordingly, the question is not can I do this? (yes, you can), it is should I do this? As you yourself have noticed, two consecutive parentheses look a bit awkward, so if there is an obvious way to avoid them, I would say it is probably for the best to do so. For example, you can instead write

This leads to a function f(x), which then ...

This leads to a function f(x). The function f(x) then ...

This leads to a function, which we will call f(x). The function f(x) then ...

This leads to a function, f(x), which then ...

This leads to a function – f(x) – which then ...

or any of a number of other possibilities. If you want to write mathematics well, I recommend that you invest some time into thinking about various different ways you can formulate sentences like this. After some practice your brain will automatically start coming up with a number of alternative ways of phrasing any given sentence, which will pay off handsomely when it comes to avoiding issues of this sort.

• I would caution against using dashes immediately before mathematical expressions. Even though in most fonts they are distinct glyphs from minus signs, it can still make it harder to parse. Apr 21 at 18:42
• @ronno Indeed, that's by far the worst option of the ones listed (which why it is the last one, although maybe I should have just omitted it so as not to mislead the OP). Apr 21 at 18:44
• (6) This leads to a function: f(x) Apr 22 at 9:10
• @MikeB I'm not sure about that. Colons separate clauses from subclauses, where the subclause depends on the one before. So "This leads to a function: the map f(x) from the previous chapter" would be fine. I would furrow my brow at your example, were I to read it in a paper. Apr 22 at 19:45
• For the OP: the statement that "invest some time into thinking about various different ways you can formulate sentences like this" leads to a key point about any writing activity (papers, code, anything): the rules being followed are a proxy for clear writing, not an actual indication of clear writing. You need to consider your audience, get inside their heads to a degree so you can view it as they will be viewing it, and then think about which of the many options available to you makes your text more clear. If you're doing that, you don't need to worry so much about rules.
– cjs
Apr 23 at 3:20

In the example you mention there is little reason to enclose f(x) within parentheses in the first place. As pointed out in the comments and another answer, writing, for example,

This leads to a function, f(x), which then ...

is likely preferable.

In other cases, I tend to follow the recommendation outlined in the Physical Review Style and Notation Guide, namely

Square brackets enclose a phrase that already contains parentheses.

Form:

Recall that the Brown-Green theory [see Eq. (2)] is still to be . . .

In my opinion, ending with ")]" looks less awkward than "))" and keeps the syntactical meaning of each bracket clear. Of course, depending on where you're publishing another style guide may dictate another solution.

• If you do this, given that in normal prose ( ) are used for parenthetical statements, I would at least do "(see Eq. [2])" instead of having the square brackets on the outside. Apr 21 at 15:38
• @terdon I could see that looking better, but being harder to automate with \eqref{}. Apr 21 at 15:46
• @terdon That would work for general writing purposes, but presumably not with “a function (f[x])”. Certainly in programming terms (and I’m guessing also in mathematics), square and round brackets have different functions, and you can’t simply adjust them to the containing typography for aesthetic purposes – a function with an argument is quite different from an array element, for instance. Apr 23 at 10:37

In general there is nothing wrong with having a math expression inside a parenthetical comment, even if that math expression itself uses parentheses. So something like "a periodic function (for example, sin(x))" would be fine.

However, I would consider it a bad idea for the math expression to be the only thing inside the parentheses, as in your example, since it creates confusion about whether the outer parentheses are part of the math expression (which can change the meaning). This applies even if there are no inner parentheses.

• "bracket space <stuff> space bracket" is also a bit clearer Apr 22 at 9:14
• I second this and would suggest adding an extra word to make it clearer if "f(x)" was the only contents of the parenthesis. For instance: "(namely, f(x))".
– a3nm
Apr 22 at 15:35

This is generally permissible. However, consider also adding spaces between the outer parentheses and the inner content, especially if you can use thin spaces or hair spaces. This increases legibility.

I completely agree with the other answers suggesting using commas or other approaches, but if you really want the parentheses, a simple trick to make them look a bit clearer is to use a different font for the f(x), just as I did here. Use a monospaced font for them and that should allow your reader to easily distinguish between the parentheses that are part of the text and those that are part of the mathematical notation. Something like this in LaTeX:

\documentclass{article}
\begin{document}

This leads to a function (\texttt{f(x)}), which then ...

\end{document}

Which looks like this:

The change in font, especially to a monospaced font which we are used to seeing used for code in technical documentation, makes it easy for the eye to separate the outer and inner parentheses.

• A coma, as opposed to a comma, seems a bit extreme ;) Assuming f(x) shows up in more than one place, I would suggest that it should be written in a consistent font. Apr 21 at 15:44
• lol, thanks @Anyon, coma averted. Yes, I would use the same approach in all cases and clearly indicate what is prose and what is mathematical notation or code with a different font. Apr 21 at 15:47
• This goes against the common conventions in mathematical texts, however. I would consider the tt font appropriate only if you are speaking about the computer implementation of a function in a programming language, not about a mathematical function. Apr 21 at 17:41
• @FedericoPoloni I'm sure you're right, my field isn't mathematics. I did also try with a function ($f(x)$) but that wasn't as clear so I didn't suggest it. Apr 21 at 18:04