Brackets in writing
In American usage, “brackets” on its own usually means square brackets. Their main jobs in prose:
- Clarifying a quotation: “He [the governor] signed the bill on Friday.” The bracketed words are yours, not the speaker’s.
- Adjusting a quote to fit your sentence: “[T]he results were clear.” The bracket shows you changed the capital letter.
- Flagging an error with [sic]: “Their [sic] going to win” shows the mistake was in the original.
- Parentheses inside parentheses: (see the 2023 report [page 12] for details).
Keep bracketed insertions short and faithful. Changing the meaning of a quote with an insertion misleads readers as much as a misquote.
Brackets in math, science and code
- Intervals: [0, 1] includes both endpoints; (0, 1) excludes them; [0, 1) includes 0 but not 1.
- Chemistry: [H⁺] means the concentration of hydrogen ions.
- Linguistics: phonetic transcriptions go in brackets, as in [kæt].
- Arrays and lists:
[1, 2, 3]in JavaScript, Python and JSON;items[0]reads the first item. - Markdown links:
[link text](https://example.com). - Regular expressions:
[aeiou]matches any one vowel; escape a bracket with a backslash to match it literally.
Look-alikes: 【 】 (lenticular brackets) and 「 」 (corner brackets) are used in Chinese and Japanese text, and ⟦ ⟧ (white square brackets) appear in math and computer science.
Typing brackets on phones and in LaTeX
- US keyboard: press [ and ] directly, no Shift needed. With Shift, the same keys type { and }.
- iPhone: open the numbers keyboard, then tap #+=. [ and ] are the first two keys.
- Android (Gboard): on the second symbols page.
- LaTeX: type them directly in text and math. Use
\left[and\right]to make them grow with tall content such as matrices or fractions. - Spreadsheets: Excel uses brackets in structured references to table columns, such as
Sales[Amount].
Frequently asked questions
How do I type square brackets?
On a US keyboard, press the [ and ] keys to the right of P. No Shift is needed.
When do you use square brackets in writing?
To add or change words inside a quotation, to flag errors with [sic], and as parentheses inside parentheses.
What does [sic] mean?
It is Latin for “thus” or “so.” It shows that a mistake appears in the original quote.
What is the difference between square brackets and parentheses?
Parentheses ( ) hold your own asides. Square brackets [ ] mark editorial additions to someone else’s words.
Unicode data: Unicode Character Database 18.0.0 (unicode.org).