Colon Before an Explanation or List (Where 'Namely' Is Implied)
The Colon
Rulebase Summary
Use a colon before an explanation or list when you could mentally insert the word 'namely' before it and it would make sense. The words before and after the colon are nouns or pronouns in apposition — the material after the colon renames or specifies what came before.
If the word 'namely' actually appears in the sentence, use a semicolon before it and a comma after it instead of a colon.
This pattern also applies to incomplete introductory expressions like 'Just so I'm clear:' or 'So I have a complete picture:' when they are spoken as a preface followed by a pause — use a colon to introduce the summary that follows.
Examples
A. He had one goal -- to get the contract signed before the deadline.
A. He had one goal: to get the contract signed before the deadline.
Colon introduces what 'namely' could precede.
A. Two departments handled the claim, billing and legal.
A. Two departments handled the claim: billing and legal.
Material after the colon renames what came before.
Transcript Notes
Listen for inflection: if expressions like 'Just so I'm clear' are spoken as a standalone preface with a pause before the next idea, use a colon. If they flow smoothly into the next clause as a true introductory clause (same subject perspective), use a comma instead.
Signal words like 'the following,' 'as follows,' 'this,' and 'these' are extra clues that a colon should be used — the colon points out or anticipates what is coming. However, when another sentence intervenes between the introduction and the material the colon would point to, the colon drops out.
Parenthetical additions such as 'that is,' 'for example,' or 'e.g.' do not change the colon rules — the colon simply precedes the parenthetical expression.
Style Guide References (3)
Morson's
BGGP
BGGP