A colon promises that something is about to be provided. As pictured above, it consists of one period-sized dot above another. It is different in both appearance and function from the semicolon ( ; ), which consists of a dot above a comma.
Uses of colons
Introducing a phrase or clause
A colon may be used to introduce a phrase or clause that represents a step forward from what came before. The movement may be from a premise to a conclusion, from an introductory phrase to a main theme, from a general statement to a particular case, or from a cause to an effect. For example, these writers use colons well:
Among the many reverberations of President Obama’s election, here is one he probably never anticipated: at least 32 African-Americans are running for Congress this year as Republicans … [New York Times]
While law enforcement officials don’t have exhaustive details of his travels after he was naturalized, one trip in particular stands out: He left New York on June 2, 2009, on an Emirates flight to Dubai. [Wall Street Journal]
His “three ways to be influential in American politics,” he said, were: make donations to political parties, establish think tanks, and control media outlets. [New Yorker]
Non-clausal phrases that follow colons (as in the third example above) should be uncapitalized. Style guides differ on whether an independent clause after a colon should be capitalized. British and Australian style guides generally frown upon capitalizing the letter immediately following the colon, unless it’s being used to introduce paraphrased speech, quoted material, dialogue (as in the script of a play), or a set of bullet points. Even within the United States, as the first two examples above show, some major publications capitalize, and some don’t. When using U.S. English, it’s usually a good idea to capitalize when the colon introduces multiple sentences. When the content before and after the colon forms a single thought, capitalization is not necessary.
Introducing a list
A colon may be used to introduce a list of items—for example:
Petrie’s concerns with wind turbines can be grouped in three areas: mortality, impact on migration and impact on foraging. [Tillsonburg News]
Introducing a self-contained quotation
A colon may be used to introduce a self-contained quotation—for example:
She added: “The law enforcement work in this case was truly exemplary.” [New York Times]
A comma may also work in this case. But when it comes to introducing a longer quotation that warrants a block quote, a colon is necessary.
A colon follows a salutation in formal correspondence—for example:
To whom it may concern:
Dear Mr. Roeper:
A colon may be used between a title and subtitle (The Story of Civilization XI: The Age of Napoleon), between a biblical chapter and verse (Exodus 2:12), and between the hour and minute in time (11:15).