Punctuation Series: Parentheses and brackets

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Beth Battrick
Writer and editor @ Teaspoon Consulting

Punctuation is the set of marks that give depth, pace and force to our words. Much like the dynamics in written music, punctuation gives the reader the extra information they need to secure the tone of the text and deepen their understanding. The Punctuation series is a collection of articles detailing the use of particular punctuation types, to help you use these precision tools to their fullest advantage.

Parentheses and brackets

Text is rarely a solid block of equally significant data. Words offer shades and subtlety, extraneous and supporting information, comments and asides. A good writer knows how to use their tools to prioritise the information they offer to the reader.

Parentheses and their related bracketty friends are a way of setting a string of text aside from the rest of the sentence, for one reason or another. When and how to use them varies across fields and purposes.

A quick word on terminology: in US English, "brackets", without any other qualification, indicates square brackets: [ ]. In most British English dialects, "brackets" indicates parentheses: ( ). In order to keep things clear and unambiguous around here, I'll refer to each by their most precise names.

What are they for?

The primary point of brackets and parentheses in written English is to set aside text in order to distinguish it from the main text. This can be for referencing/citation purposes, but also for interjections, comments, explanations and asides.

Parentheses and brackets have a huge range of specialised purposes in other areas (e.g. computing, maths, science, translations, semantics, etc.). This article concentrates specifically on the use of parentheses and brackets in written English.

What bracket is that?

I don't know if you've noticed, but there's a whole family of vertical enclosing punctuation marks. Seriously: check out your keyboard. You've got your stylish, curvy parentheses ( ) on the 9 and 0 keys; your firm and determined angle brackets < > on the comma and full stop keys; and then there's the square brackets [ ] and curly brackets { } that share the keys on the far right of the row under the numbers. There's heaps!

There are even more if we expand our scope to include languages other than English: things like floor and ceiling brackets (⌊ ⌋ ⌈ ⌉) and guillemets (‹ › and « »). These brackets are most commonly used in European and Asian languages for quote marks (i.e. to indicate quoted speech or text), so they're outside this article's scope.

When to use which bracket

Parentheses: ( )

Parentheses are probably the most familiar bracket type to readers. They are used as a way of indicating additional and/or supportive text. The pair of parentheses wraps around some extra information in this sentence:

Alan's reckless disregard for the cage lock (he once used it to force the cap off a beer bottle) had weakened it over time.

As you can see, this sentence would still make perfect sense if the parentheses and their contained text (the parenthetical text or sometimes just the parenthetical) were removed. The parenthetical adds extra information: useful, but maybe not as essential as the rest of the sentence.

Vivian was struck dumb (for perhaps the first time in her life) by Alan's behaviour.

A parenthetical can be an entire sentence, either embedded within a higher sentence or as a complete aside to the preceding sentence:

Vivian burst into tears (Why was she so embarrassed? She'd known him for years!) and ran away.

In this example, the parenthetical offers something of an insight into Vivian's thoughts: the use of whole sentences, rather than fragments, within the parentheses, indicates the need for each sentence within the parentheses to use its own terminal punctuation (a question mark and an exclamation mark, respectively).

Alan felt a little sheepish about the broken lock. (He decided not to tell Vivian about the time he used the lock to smash a coffee mug just to see which was stronger.)

In this example, the parenthetical creates the impression of an aside from the author to the reader: again, since the parentheses contain a whole sentence rather than a fragment, the sentence's terminal punctuation goes within the parentheses.

When your parenthetical text is at the end of the sentence (immediately before the terminal punctuation), you will need to figure out whether extra punctuation is needed inside the parentheses. Since the parenthetical text is nested within the sentence, the sentence's final punctuation will go outside the closing parenthesis:

Alan began to mop up the mud (and the blood).

When the parenthetical text contains complete sentences (and their terminating punctuation, as explained above), you'll need to include the final terminating punctuation inside the parentheses as well as the sentence's terminating punctuation outside the closing parenthesis:

Vivian walked proudly out of the women's toilets (He mustn't know she was crying! It was too, too embarrassing!).

You can nest parentheses within other parentheses, but do so cautiously. Sometimes there's no way around it, such as when the additional parenthetical information contains a bibliographic reference:

Fogmore (1998b:45) suggests that all toads are derived from a single species (Jenson's work on other amphibians took exception to this assertion (Jenson 1978) but researchers have generally dismissed his research) but that all frog species were uniquely evolved.

Including an additional parenthetical string of text within the first parenthetical string is possible, but the results tend to be convoluted:

Alan was unashamed of his lock-weakening behaviour (although he was embarrassed to have been discovered (Why did Vivian have to go nosing about like that?) and he didn't like being embarrassed).

While it can be a humorous technique in informal writing, generally, avoid nesting parentheses in formal or professional writing. It requires the reader to keep multiple unresolved strings of thought in their mind until the end of the sentence, and this can be distracting and confusing.

If you are determined to nest your parentheses, you may choose (or be compelled by a style guide) to alternate parentheses with square brackets.

While undertaking the cleanup he railed against the discomfort (he was so unused to mopping and scrubbing that his hands [which were already sore] became swollen and red) and planned revenge.

Square brackets [ ]

Square brackets in English writing are most frequently used to offer information about the interpretation of a writer, editor or translator. They are used to show points in text where something has been added, omitted, altered, or left as it is despite being wrong.

Where parentheses indicate an additional comment in the flow of text and contribute to shades of meaning, square brackets excuse the parenthetical comment from the text's content and directly address matters of grammar, structure and interpretation of the text.

When a quote needs to be adjusted to match the grammatical flow of a sentence, square brackets indicate what has changed. For example, if a public figure says:

The unicorn is, without any doubt in my mind whatsoever, the greatest menace facing our culture, and perhaps our very livelihood as a species. There is no question: they are violent, unpredictable, amoral equines that we do not want running around our schools. Unicorns must be stopped. Unicorns must go.

This may be adapted (for example, by journalists, bloggers, and anyone else who is reporting on this sweeping statement) to maintain the grammatical structure of a sentence:

Today, outspoken starlet Whizzer offered his opinions on unicorns: "[they are] the greatest menace facing our culture".

The square brackets above indicate that something from the original text has been replaced with a substitution that preserves the meaning of the original and the grammatical structure of the quoting sentence.

Instead of replacing text, square brackets can also offer clarifying information that may have been left out of the original quote for brevity:

Whizzer insisted "they [unicorns] are violent, unpredictable, amoral equines".

Similarly, if the text quoting Whizzer's unsought diatribe makes use of a quote beginning with a capital letter, square brackets are used to indicate that the capital letter has been replaced with a lower-case letter (since it's no longer at the start of a sentence):

Whizzer's furious insistence that "[u]nicorns must go" is not the first unprovoked rant from the performer.

Square brackets also have a role in indicating where text has not been changed, but the reader could be forgiven for thinking it had. This is especially helpful when the quoted text contains errors:

Whizzer continued his rant on social media, writing in a blog post "Unicorns are dum [sic] and shouldn't be allowed!!"

Square brackets can also be used alongside translated text to include the original:

While travelling in Sweden, you should not to help yourself to the roasted pork ribs [revbensspjäll].

Finally, square brackets can be used where someone involved in preparing the text needs to address the reader directly. The most common example would be something like:

[Editor's note: The reproduction of Whizzer's comments on unicorns should not be construed as an endorsement.]

Angle brackets < >

Angle brackets are very rarely used in English prose. However, there is a particular case you should be aware of. In some style guides, angle brackets are used to set aside URLs:

For further information, see Whizzer's blog <http://www.ihateunicorns.com>.

This is usually done in order to avoid any confusion about the line breaks and punctuation that may be used around a URL. For example, a bibliography citing a very long URL will, out of necessity, break the URL over a line break: using the angle brackets helps to clarify to the reader that the text over the line break is still part of the URL. Similarly, the use of angle brackets clearly separates the URL from the sentence's terminal full stop.

However, as URLs have become a matter of course in writing and readers are now generally familiar with them, I would argue that isolating them using angle brackets is usually unnecessary. (As ever, default to your ruling style guide.)

Curly brackets { }

It saddens me to say it, but curly brackets have almost no place in English writing. I am saddened because they are pretty and interesting punctuation marks. Maybe we could introduce them to mean whispering or drunken slurring? We're going to need a Kickstarter for this.


Parentheses and brackets, like all punctuation, are precision tools. They allow the writer to introduce new information in a nuanced and prioritised way. An explanation in parentheses supports the facts given, without dominating or intruding. An explanation in square brackets allows the writer, editor or translator to directly address the reader and resolve possible confusions about the content of the text.

Happy punctuating!