This post outlines the functions of punctuation marks employed within a sentence: the comma, the semicolon, the colon, and ellipses.
A comma performs a number of functions, including
- setting off elements of a list (“I’m going to order soup, salad, and an entrée”)
- combining with a conjunction to separate two independent clauses (“She ordered dinner, but she declined the dessert menu”)
- separating a preceding dependent clause from the main clause (“Depending on the size of the entrée, I might not order dessert”)
- separating a nonrestrictive relative clause from the main clause (“We were overwhelmed by the menu, which was six pages long”)
- setting off an adverb from the main clause (“Ordinarily, I would not order dessert”; “I would, ordinarily, not order dessert”; “I would not order dessert, ordinarily”)
- framing parenthetical phrases (“I will, just this once, order dessert”)
- setting off an appositive (“My favorite dessert, cheesecake, is missing from the menu”)
- setting off coordinate adjectives (“I feel like having a big, thick slice of cheesecake for dessert”)
- setting off an attribution from a quotation (“My friend said, ‘I’m going to order dessert’”)
- setting off one or more words identifying the subject of direct address (“John, are you going to order dessert?”)
- setting off a date from a year and parenthesizing the year (“January 1, 2018, dawned just like any other day”)
- setting off a city name from a state or country name and parenthesizing the state or country name (“Lebanon, Kansas, is the geographic center of the contiguous United States”)
- setting off a surname from a given name when the first-name, last-name order is inverted (“She is listed as ‘Doe, Jane’”)
- indicating ellipsis of one or more words (“Everything was as I remembered it—the church was white, the barn, red”).
A comma should not separate a subject and a verb (as in the erroneous sentence “The tiramisu, is sublime”) except when it is closing a parenthetical phrase (“The tiramisu, as expected, is sublime”) or setting off repetition of a verb (“What it is, is sublime”). Likewise, a verb and its direct object should not be split asunder (as shown in the incorrectly punctuated sentence “She intuitively grasped, that she was in trouble.”)
Another error that involves a comma is a comma splice, in which a comma, rather than a stronger punctuation mark such as a semicolon or a dash, appears between two independent clauses not separated by a conjunction, as in “You see a half-empty glass, I see a half-full one.” (An exception can be made for brief declarations, as in Julius Caesar’s famous summary “I came, I saw, I conquered.”)
The semicolon has two primary functions. First, it unites two closely related independent clauses, as in “You see a half-empty glass; I see a half-full one.” (In such cases, it takes the place of a period or a conjunction; including both a semicolon and a conjunction is an error.) Second, it replaces two or more commas in an in-line list (a list with a sentence) when one or more of the list items itself includes commas, as in “The names, as listed, are Doe, Jane; Jones, William; and Smith, John” or “I spotted many squirrels; several deer; and a hawk, an osprey, and a heron.” (If the list organization is obvious, as when list items begin with distinct verbs, commas may be employed, as in “She shopped at the supermarket, visited the bank and the credit union, and ran errands at the hardware store, the drugstore, and the dry cleaner’s.”)
Earlier usage included setting off coordinate clauses in complex sentences or to otherwise signal a more pronounced pause than a comma would suggest, but these approaches, especially the former, are outdated.
In quoted material, a semicolon always follows a close quotation mark. Also, the mark may seem too formal in the midst of a sentence in quotation marks; a dash more clearly conveys a transition to a separate assertion or idea, as in “Mary said, ‘Don’t go in the abandoned house—it’s not safe in there’” rather than “Mary said, ‘Don’t go in the abandoned house; it’s not safe in there.’”
A colon precedes
- quoted material set up by a complete statement rather than an attribution (“His reply was succinct: ‘Not a chance’”)
- an explanation (“We declined the invitation primarily for one reason: He insists on driving, and we don’t feel safe as his passengers”)
- a list (“The meal consists of the following courses: appetizer, salad, entrée, and dessert”).
It is also employed between pairs of numbers
- to represent ratios (“The results indicate a 5:3 ratio”)
- in references to time (“The next train is at 1:35”)
- in numerical representations of elapsed time (“The record stands at 3:26.00”)
- when citing biblical verses (“John 3:16 expresses the same sentiment”).
A colon also separates a book’s title and subtitle or, in bibliographies, the city where a publisher is located and the name of the publisher. In formal writing, it follows the salutation.
A colon always follows a close quotation mark.
Ellipsis means “omission,” but it primarily refers to a succession of three periods, called ellipses, usually interspersed with letter spaces, or a single symbol representing three periods. Style guides differ in which form is preferred, but the ellipsis symbol looks cramped, and use of ellipses (a series of periods) is more visually pleasing.
Ellipses represent omission of one or more words in the middle of a sentence (“A friend . . . knows all about you and still loves you”); generally, they are unnecessary when omitting what precedes a partial quotation.
The use of ellipses as terminal punctuation will be discussed in a separate post.
Uses of the dash are detailed in this post.
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Original post: A Guide to Internal Punctuation