An appositive phrase extends a sentence by adding more information in apposition (meaning “related to” or “juxtaposed with”) to a word or phrase preceding it. This post describes how to use each of four forms of punctuation to extend a sentence by adding an appositive phrase.
A colon signals to the reader that what follows is an expansion or explanation of what precedes it: The colon is equivalent to an equals sign in mathematics. (The preceding statement is an example of expansion.)
The traditional rule of capitalization after a colon is twofold: If the text that follows the colon as an expansion or explanation is a phrase or a single sentence, the first word of that passage should not have an initial capital letter. If the text is more extensive, the first word of each related sentence should be capitalized. (The preceding statement is an example of explanation.)
This rule is not universally accepted, and I’m among the heretics: I prefer to initial-cap what follows a colon if it is a complete statement of one or more sentences, because I think that the distinction between incomplete and complete statements is more logical than the standard criterion.
The colon also appositively signals that a quotation or a list follows, as in “This truth is universal: ‘Just because you can doesn’t mean you should’” and “I bought three tools: a hammer, a wrench, and a screwdriver.”
A dash can substitute for each of the other three punctuation marks described here; the choice is based on tone rather than sentence organization. A dash represents a sudden or abrupt shift — it’s a dramatic device to set the reader up for a change of syntactical form or for a revelation or a punch line.
A pair of dashes can be employed parenthetically, but that use does not apply to appositive phrases.
(Read more about dashes — and search the site for “em dashes” for more posts that discuss the topic.)
An ellipsis, a series of three dots that separate one part of a sentence from another (also known collectively as ellipses), indicates an intentional or unintentional pause caused by person being at a loss for words or hesitating because of some emotion such as doubt or fear or for dramatic effect. (Ellipses are often interspersed with letter spaces — a more aesthetically pleasing style — though some publications omit the spaces or use a single-character ellipsis.)
When an ellipsis concludes a sentence, it represents faltering speech, and it marks omission of one or more words from quoted material, but these uses do not apply to appositive phrases.
The semicolon is similar in name and appearance to the colon, but its function is unrelated; it serves as a weak period, as employed here, or as a strong comma, as shown in the next paragraph. In its weak-period guise, it marks the end of one statement and the beginning of another; however, it is appropriate in place of a period only if the second statement is closely related to or dependent on the first one. Note that when a semicolon appears in such a case, no coordinating conjunction (such as and or but) should follow it. (However, when the conjunctive adverb that begins this sentence, or others such as moreover or therefore, follows a semicolon, as occurs earlier in this paragraph, a comma should follow the word.)
A strong-comma semicolon is one used in place of two or more commas when the elements in a run-in list are themselves lists, as in this sentence: “The three most frequent color schemes in flags are red, white, and blue; red and white; and, tied for third place, red, yellow, and green and red, white, and green.” (Note that not all list items must include internal punctuation.)
Many writers are reluctant to use semicolons because they do not understand how to use the punctuation mark correctly or consider it overly formal, but its roles are simple and helpful.