What are Parentheses and Brackets?
Parentheses (round brackets) enclose material that is supplementary to the main sentence — additional information, clarifications, abbreviations on first use, cross-references, or asides. The sentence must make complete grammatical sense without the parenthetical content. If removing the parenthetical breaks the sentence, it should not be in parentheses.
Square brackets [ ] serve a different purpose: they mark editorial additions or changes within a quoted passage. When you quote a source and need to add a word for clarity, change a verb form, or note an error in the original, you enclose the addition or change in square brackets. This signals to the reader: these are the editor's words, not the original author's.
The choice between parentheses, commas, and em dashes is a stylistic one: commas integrate an aside quietly into the flow, em dashes draw attention to it emphatically, and parentheses mark it as clearly secondary. Each creates a different reading experience. In academic writing, parentheses are preferred for cross-references, citations, and abbreviation introductions.
Parentheses and Brackets — Their Jobs
The key distinction: parentheses are yours to use in your own writing. Square brackets are for modifying or clarifying text you are quoting from someone else.
Parentheses ( ) = supplementary information in your own text / Square brackets [ ] = editorial additions within someone else's quoted textParentheses ( ) — Uses
| Use | Example | Note |
|---|---|---|
| Supplementary information or aside | The research team (based in Nairobi) published their findings last month. | Remove the parenthetical — sentence still works. |
| Abbreviation on first use | The World Health Organization (WHO) issued a warning. | After this, use WHO alone. |
| Cross-reference or citation | The methodology is explained in detail elsewhere (see Chapter 3). | Standard in academic writing. |
| In-text citation (academic) | A strong correlation was found (Ahmed et al., 2022). | APA, Chicago, and similar citation styles. |
| Plural possibility | Please submit the form(s) required. | Signals either singular or plural is possible. |
| Numbers in a list within prose | The proposal must address three issues: (1) budget, (2) timeline, and (3) staffing. | More formal alternative to a–b–c. |
Square Brackets [ ] — Uses in Quotations
| Use | Example | Note |
|---|---|---|
| Adding a word for clarity | She noted that '[the committee] had not been informed'. | Original said 'they' — editor adds the noun for clarity. |
| Changing a verb form to fit your sentence | He 'claim[ed] that the data was fabricated'. | Changing 'claims' to 'claimed' to match past narrative tense. |
| Marking an error in the original (sic) | The report stated 'the data was [sic] incomplete'. | 'sic' = thus (Latin) — means the error was in the original. |
| Replacing an ellipsis (editorial) | 'The study found that [exercise] [...] reduced stress'. | Square brackets make it clear the omission and addition are editorial. |
Punctuation with Parentheses
| Rule | Example | Explanation |
|---|---|---|
| Comma after closing parenthesis (if comma needed) | The data (see Table 3), which was collected in 2022, confirms the trend. | The comma follows the closing parenthesis, not precedes it. |
| Period inside for standalone sentence in parentheses | The results were consistent. (See Appendix B for the full data.) | The full sentence in parentheses has its own period inside. |
| Period outside when parenthetical is part of the sentence | The results were consistent (see Appendix B). | The period belongs to the outer sentence — after the closing parenthesis. |
How to Use Parentheses Correctly
Parentheses vs commas vs em dashes
The same supplementary information can be enclosed with commas, em dashes, or parentheses. The choice signals how important the aside is. Commas keep it in the flow; em dashes emphasise it; parentheses deprioritise it. Academic writing typically uses parentheses for citations and cross-references, and commas for relative clauses and appositions.
- Commas — integrated, quiet: The director, who joined last year, proposed the change.
- Em dashes — emphatic: The director—who had lobbied for months—finally proposed the change.
- Parentheses — secondary: The change was proposed by the new director (appointed January 2023).
Square brackets and [sic]
When a quoted source contains an error (spelling, grammar, or factual), you are not permitted to correct it because you must quote exactly. Instead, add [sic] (Latin: 'thus') immediately after the error to signal: yes, this is what the original says; the error belongs to the source, not to me.
- Error in original: The report stated that 'the data was [sic] incomplete'.
- Wrong: The report stated that 'the data were incomplete' (correction without notice = changing the original)
- Right: The report stated that 'the data was [sic] incomplete' (preserving original + flagging the error)
Parentheses and Brackets Warning Signals
Round Parentheses ( ) vs Square Brackets [ ]
Both enclose supplementary material, but the source of that material differs completely: parentheses are yours; square brackets mark editorial intervention in someone else's words.
Round parentheses — your own supplementary text
The World Health Organization (WHO) published new guidelines.
The abbreviation in round brackets is your own addition to your own text.
Square brackets — editorial addition inside a quotation
She noted that '[the WHO] had not been consulted'.
The original said 'they' — the editor's addition of '[the WHO]' is marked with square brackets to distinguish it from the original author's words.
Common Mistakes
Putting a comma before an opening parenthesis
✗ The data, (collected in 2023) confirmed the hypothesis.
The data (collected in 2023) confirmed the hypothesis.
The comma, if needed, goes after the closing parenthesis, not before the opening one. The parenthetical is inserted into the sentence — no comma precedes the insertion.
Using round brackets instead of square brackets in a quotation
✗ He stated that '(the committee) had reached a decision'.
He stated that '[the committee] had reached a decision'.
Round brackets are your own supplementary additions in your own text. Inside a quotation, editorial additions must use square brackets to distinguish your words from the original author's.
Parenthetical that breaks the sentence when removed
✗ The (methodology section) explains the sampling approach.
The methodology section explains the sampling approach. / The sampling approach (see methodology section) is described on page 14.
Content enclosed in parentheses must be supplementary — the sentence must read correctly without it. If removing the parenthetical creates a grammatically broken sentence, the content is not supplementary and should not be in parentheses.
Period before the closing parenthesis for a mid-sentence parenthetical
✗ The findings were significant (see Table 3.)
The findings were significant (see Table 3).
When a parenthetical is part of a larger sentence, the period belongs to the outer sentence — placed after the closing parenthesis. A period inside the parentheses is only used when the parenthetical is a complete, standalone sentence in its own right.
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