Colon (letter)

The colon (:) is a punctuation mark consisting of two equally sized dots centered on the same vertical line. In writing, it serves a variety of functions, primarily to introduce or elaborate on something that precedes it.

Functions:

• Introduction: A colon can introduce a list, quotation, explanation, or example. The material following the colon clarifies or expands upon what came before. For example: "I need the following items: milk, eggs, and bread."

• Elaboration: A colon can signal that the second part of a sentence provides more detail or explanation for the first part. For example: "There was only one explanation: he had forgotten."

• Separation: A colon can separate independent clauses when the second clause explains or illustrates the first. For example: "He had a good reason to be happy: he had just won the lottery."

• Ratios: Colons are used to express ratios, such as in mathematics and nutritional information. For example: "The ratio of men to women was 3:1."

• Time: In many cultures, a colon separates hours and minutes in time notation. For example: "The time is 3:15 PM."

• Bibliographic Citations: Colons are used in bibliographic citations, particularly to separate a title from its subtitle. For example: "The Great Gatsby: A Novel."

• Salutations: Colons are commonly used after the salutation in formal letters. For example: "Dear Mr. Smith:"

Style Considerations:

• In American English, a complete sentence following a colon is typically capitalized. In British English, it is not.
• The usage and necessity of a colon often depends on the flow and clarity of the sentence. Sometimes, a comma, em dash, or semicolon might be a more appropriate choice.