The Colon Introduces, and That Is All It Does
The colon has a single function: it announces that what follows explains, expands or lists what came before.
That sentence used one. The half before the colon set up an expectation; the half after delivered it.
The test
What comes before a colon must be a complete sentence. What comes after need not be.
- Right: She brought three things: a map, a torch and a flask.
- Wrong: She brought: a map, a torch and a flask.
- Right: The ingredients are simple: flour, water and salt.
- Wrong: The ingredients are: flour, water and salt.
This is the error, and it is everywhere in business writing. The ingredients are is not a sentence; it is a sentence waiting for its object. Interrupting it with a colon leaves the verb dangling.
Two fixes: delete the colon, or complete the clause. The ingredients are flour, water and salt works. So does The ingredients are as follows: flour, water and salt.
The four things it introduces
A list. Three candidates remained: Adams, Bell and Cross.
An explanation. The reason was obvious: nobody had checked. This is the most useful and least used. It replaces because and lands harder.
A quotation. She had one rule: “Never explain, never complain.”
An emphatic single word. After three years, the project produced exactly one thing: paperwork. The colon creates a pause that gives the last word its weight.
Capital or lower case after it
- Chicago: lower case, unless what follows is more than one sentence, or is a quotation, or is a proper noun.
- AP: capitalise if what follows is a complete sentence.
British usage generally follows the Chicago pattern. As always, pick one.
Colon or semicolon
The distinction is directional, and once you see it you will not confuse them again.
- A colon points forward. The second half explains the first.
- A semicolon balances. The two halves are equals.
- The meeting was cancelled: nobody could attend. The second clause is the reason.
- The meeting was cancelled; the report was delayed. Two related facts, neither explaining the other.
Where it also turns up
Outside sentences, the colon does mechanical work that follows no rule about complete clauses: times (14:30), ratios (3:1), titles and subtitles, letter salutations in American usage (Dear Ms Hall:), and speaker labels in scripts.
None of these need the test. Everything inside a sentence does.
Checked against Merriam-Webster, the Chicago Manual of Style and the AP Stylebook. Spotted an error? Tell us — see our editorial policy.
