Colons signal readers to keep reading because related thoughts or a list will follow. In this role, colons differ from periods, semicolons, and even commas, all of which signal a pause or even a full stop.
Colons link related thoughts, one of which must be capable of standing alone as a sentence.
Colons emphasize the second thought (unlike semicolons, which emphasize both thoughts equally, and dashes, which emphasize the break in the sentence and can emphasize the first thought).
Colons shift emphasis forward: They tend to make the second thought the most important part of the sentence. When such is the case, the colon indicates that explanation or elaboration follows:
- The Franklin Shipyard needed one thing to remain solvent: to win the Navy’s supercarrier contract.
- The Franklin shipyard needed one thing to remain solvent: It had to win the Navy’s supercarrier contract.
NOTE: The two complete thoughts in the second example could also appear as two sentences:
- The Franklin Shipyard needed one thing to remain solvent. It had to win the Navy’s supercarrier contract.
However, linking these thoughts with a colon emphasizes their close connection. Writing them as two sentences is less emphatic if the writer wishes to stress that the one thing Franklin needs is to win the contract.
Colons introduce lists or examples:
Our management-development study revealed the need for greater monitoring during these crucial phases:
- Initial organization
- Design and development
- Fabrication and quality control
The Mars Division’s audit of field service-personnel centers found the following general deficiencies:
- Service personnel do not fully understand the new rebate policy.
- Parts inventories are inadequate.
- The centralized customer records are not operational, although the computer terminals have all been installed.
NOTE 1: A colon need not follow a heading or subheading that introduces a list. The heading itself is sufficient; a colon is redundant.
NOTE 2: The items listed do not require periods unless they are complete sentences. See LISTS.
Colons separate hours from minutes, volumes from pages, and the first part of a ratio from the second:
- The deadline is 3:30 p.m. on Friday.
- See Government Architecture 15:233.
- The ratio of direct to indirect costs is 1:1.45.
Colons follow the salutation in a formal letter:
- Dear Ms. Labordean:
- Dear President Crouch:
- Dear Clarence Johns:
Colons separate titles from subtitles:
- Government Architecture: Managing Interface Specifications