The Editor’s Manual
Free learning resource on English grammar, punctuation, usage, and style.
Commas, colons, semicolons, dashes, and other punctuation marks that make you tear your hair out.
Parentheses set off information that may be useful but is tangential to the primary meaning of the passage. Square brackets enclose editorial clarifications to quoted text. Square brackets are also used as brackets within brackets.
Use square brackets within parentheses to show brackets within brackets. In British style, round brackets are used within round brackets. Avoid using nested parentheses in U.S. writing.
Brackets enclose editorial comments and corrections, and any text added to a quote by someone other than the original writer. “Sic” in brackets indicates an exact reproduction. Brackets also set off parenthetical material that appears in text already within parentheses.
Use parentheses (or round brackets) to set off supplementary information from surrounding text. Such information should not be essential to the grammar of the sentence. Periods go within parentheses if they belong to the parenthetical matter but outside otherwise.
Don’t use a comma before “who” when it presents information necessary to meaning (a restrictive clause). Do use a comma when “who” introduces an optional description (a nonrestrictive clause).
Both a colon and an em dash introduce new information that explains or builds upon something that precedes it. The colon is quieter; the dash is more emphatic and dramatic.
Use a colon only after a grammatically complete sentence to introduce a list. Don’t use a colon between a verb and its object. Don’t use a colon after a title, heading, or caption for a list.
Don’t use a comma with “that,” either as a relative pronoun or a conjunction. “Which” usually introduces an optional description, which you should enclose in commas. No commas are used if “which” introduces essential information.
When an abbreviation ending in a period is followed by a punctuation mark like a comma, colon, semicolon, or dash, use both the period and the punctuation mark. But use only a single period after an abbreviation at the end of a sentence.
If an abbreviation ending in a period also ends a sentence, use just one period, not two. With parentheses, place a period after the closing parenthesis to end the larger sentence.