Sometimes students avoid using colons because they do not understand their usefulness. Colons indicate that further explanation of an idea follows the punctuation: for example, a list, a definition, a quote or other detail such as a subtitle. Other possible uses consist of separating ratios, indicating time, ending the opening address in formal correspondence, and special citation cases in style guides such as Modern Language Association and American Psychological Association.
Further Detail with Colons
Use a colon after a complete sentence when a summary, a list or further detail comes next, as in the sentences, "He attended the conference with two co-workers: Jan and Bill" and "This cereal is healthy: It contains high fiber." Capitalize the word after the colon or leave it lowercase, according to the style guide being used. When following the colon with a quote, capitalize the first word in the quote: "Jefferson said it best: 'All men are created equal.'" Avoid placing colons between a verb or preposition and the object. For example, "The colors are blue, green and yellow" and "Stephanie's guests consisted of her parents, her sister and her best friend" need no colons. Similarly, leave out colons after phrases like "such as."
Colons with Numbers and Documentation
Ratios such as a 3:1 ratio of students to teachers, and specific times such as 9:10, use colons between the numbers. Also capitalize subtitles and the names of publishing companies on references lists after colons. For instance, "The Boys in the Hall: Making Waves" and "New York: Bantam" use colons and capitalization properly. Students can learn these guidelines by practicing on sentences and phrases instructors provide, or by making up practice reference page entries.