The Editor’s Manual
Free learning resource on English grammar, punctuation, usage, and style.
An acronym is an abbreviation pronounced as a single word. It is treated differently from other abbreviations (such as initialisms) in edited text.
Abbreviations are acceptable in formal writing. Explain an abbreviation at first use. Avoid overuse. Avoid using them in titles and headings or to start a sentence.
Abbreviated SI and other metric units do not have a separate plural form: don’t add “s” to form the plural of an abbreviated unit of measurement (10 km, not 10 kms).
Contractions are common in speech and informal writing but avoided in formal texts.
Use commas to integrate closely related information into the flow of the sentence. Use parentheses to set off supplementary information or an afterthought from surrounding text. Use dashes to be emphatic or dramatic and make additional information or an aside stand out.
Use “sic” to indicate a grammatical or spelling mistake in the original text of a quote. “Sic” is generally italicized in formal texts. Also enclose “sic” in brackets in formal 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.
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.
Avoid starting a sentence with an abbreviation. Use the full form instead, or rephrase. An acronym (abbreviation pronounced as a word), however, is acceptable in this position.
Provide the full form of an abbreviation at first use. Write the complete term and enclose the abbreviation in parentheses, unless the term is better known in its abbreviated than full form.