THE COLON
The colon is used between clauses of compound sentences, additional clauses without a conjunction, formal quotations, and particulars in apposition with a general term, to mark the necessity of a pause greater than that indicated by the semicolon and less than that indicated by the period. The colon is much less used today than formerly, as modern writers employ shorter and less formal sentences than those of a century ago. It should always be placed outside the quotation-marks unless included as a part of the quotation itself.
Use the colon:
1. Before as, viz., that is, namely, etc., when these words introduce a series of simple particular terms in apposition with a general term: e.g., There are three genders in Latin: namely, masculine, feminine, and neuter.
2. Between two members of a sentence when one or both are made up of two or more clauses divided by semicolons: e.g., Vallie was nervous in his temperment; the Captain was calm and self-contained: Vallie was the product of the city; the Captain was the product of the world.
3. Between a complete sentence and an additional clause enlarging upon the same idea without a conjunction: e.g., Imagination {11} is essential to business success: without imagination, plans for future development cannot intelligently be made.
4. Before particulars definitely stated: e.g., These new duties of the management are grouped under four heads: first, they develop a science for each element of a man’s work, etc.
5. Before formal quotations: e.g., In a recent speech attributed to you by the daily press, you are reported to have used these words: “Good principles follow good habits.”
6. After the formal salutatory phrase at the beginning of a letter: e.g., Gentlemen:[1] When less formality is desired, the comma may be used: e.g., My dear Mother,
[1] See page [117,] §§ 2, 3, 4.
7. Between the hours and minutes in indicating time: e.g., 11 : 30 A.M.
8. Between the chapter and verse in scriptural references: e.g., Matt. 1 : 4–8, 12, 16; chap. 3; 8 : 16.
9. Between the city of publication and the name of publisher in literary references: e.g., “The Adventures of Tom Sawyer” (New York: Harpers).