The Editor's Manual
Free learning resource on English grammar, punctuation, usage, and style.
Round brackets are called “parentheses” in American English but referred to simply as “brackets” in British English. In American writing, square brackets are used within parentheses, while the British use round within round brackets (nested parentheses).
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.
Use “which” to introduce a description. As a relative pronoun, “which” connects a relative clause to the noun it describes. Differences exist between American and British usage.
“That” introduces information that is essential to meaning and not enclosed in commas. “Which” introduces additional, optional details enclosed in commas. In British usage, it also introduces essential information.
Use commas before and after the year in the American date format (May 1, 2021) but not in British (1 May 2021). No comma is needed when only the month and year are specified (May 2021).
American date format is month-day-year (May 1, 2021); British is day-month-year (1 May 2021). Use commas between day and year in American English; no commas are needed in dates in British English.
When to use which: In/into/inside/within, in/during, for/since, on/upon/onto, over/above, over/more than, under/less than, below/beneath/under/underneath, off/of, beside/besides, round/around, to/toward/towards.
Collective nouns, which refers to groups like “team,” “government,” “family,” and “committee,” are treated as singular in American but plural in British English. Use of the singular or plural verb also depends on whether you want to refer to the group as a whole or to the individual members of the group.
Periods are generally not used in abbreviations with more than one capital letter (MD, PhD). Contractions and other abbreviations with lowercase letters usually contain a period (etc., p.m., Dr.). Don’t use a period after an abbreviated SI unit (cm, dl).