Sometimes instructors mark punctuation errors in papers but do not provide explanations of what has gone wrong. Such errors are obvious to those who know the rules, but may be invisible to those who do not. Rules that typically fall into this category pertain to the following matters of punctuation:
Some punctuation errors arise from poor proofreading. Consult the page on manuscript conventions for further details.
The details of punctuation may seem trivial, but by properly punctuating you arrange the parts of your sentence logically. Punctuation should alert readers to the structure of your thought. It is the visual equivalent of vocal inflection. If you read your prose aloud, you will avoid errors of punctuation like the ones in this sentence:
The issue of abortion, is complex and, extremely controversial.The writer here did not understand that commas mark a pause, usually in the same place where someone reading aloud would stop for emphasis or breath; no one would ordinarily pause between subject and verb or between a conjunction and its appended phrase. Generally speaking, commas have four uses: to separate items in series, to bracket words in apposition, to set off an introductory phrase, or to punctuate compound and complex sentences. Unless they are very short, two independent clauses joined by a coordinate conjunction ("and," "but," "for," "nor," "or," "so," "yet") are separated by a comma:
Criticisms of Shakespeare's plays fill whole libraries, but the facts of his working career can be summarized in a brief pamphlet.Two independent clauses not connected by a coordinate conjunction are separated by a semicolon, unless they are members of a longer series of such clauses. Compare these two sentences:
Criticisms of Shakespeare's plays fill whole libraries; the facts of his working career can be summarized in a brief pamphlet.Criticisms of Shakespeare's plays fill whole libraries, the facts of his working career can be summarized in a brief pamphlet.
The first clearly presents two independent and equally important ideas; the reader sees immediately that they are to be contrasted. The second version (a "run-on sentence" or "comma splice") is initially confusing. Seeing the comma, the reader thinks a third element will follow in the series, like this:
Criticisms of Shakespeare's plays fill whole libraries, the facts of his working career can be summarized in a brief pamphlet, but the details of his married life need only a single paragraph.Readers of the second version eventually can see what is meant (and they will also see that it is incorrectly punctuated), but it is your business as a writer to make understanding prompt, not eventual. Do not overuse the semicolon, but remember that it is an important signal to the reader, indicating that a following clause is a fully independent addition to or modification of what precedes it.
A restrictive clause limits meaning or specifies which of a number of objects is intended. Such clauses are not set off by commas.
The document that Franklin produced met with favor.Non-restrictive clauses provide supplementary information not necessary to identify the subject. They are set off by commas.
The document, which Franklin produced, met with favor.In the first sentence (containing a restrictive clause), we speak of Franklin's work as opposed to someone else's; among several documents, Franklin's was favored. In the second sentence (which has the non-restrictive clause), we already know which document is under consideration, and we learn parenthetically who happened to write it.
Punctuate a series (of words, of phrases, or of clauses) with a comma after every term except the last, including the one before "and":
Bring the shells, books, boxes, and umbrella.Lightning flashed, thunder cracked, and the torrential rains began.
In general, as in the second example, put shorter items in the beginning. If the terms within the series require commas themselves, as do appositional insertions, then separate the terms with a semicolon:
The members included His Highness, Ralph, Prince of Wales; Roger, Second Vice-Earl of Nantucket; Justice Spade; the Very Reverend Dr. Mack, Bishop of Anglia; and Eustace Gordon, Lord Hello.The punctuation makes it clear that five people are named.
Interpolations or modifications can be put inside commas, like this, if they are quite brief. If they are longer or more disruptive, you may wish to choose between dashes--like this--or parentheses (which, you will remember, always travel in pairs). There are several nuances to consider in this choice. Unlike parentheses, the dash can be used to break the flow of a sentence at a single point--dashes are more arresting and emphatic. Parentheses, on the other hand, allow you to digress or make oblique reference to your subject. Both devices can be useful, but try not to wear them out.
The colon (:) signals that the next part of the sentence exemplifies or describes in different terms the preceding part. Usually it introduces a definition, specification, or example. The colon may introduce a phrase:
His purpose was clear: to offend all those who heard him.It may introduce a clause or series of clauses:
His speech was an offense: it disturbed the Dean, outraged the alumni, and blackened the name of the university.But it should not divide elements of a sentence that do not require division, as in:
Your speech was an offense against: the Dean, the University, the Council of Churches, and God.The last example does not require a colon.
In American (not British) usage, put commas and periods inside closing quotation marks, and semicolons and colons outside.
He said, "Never again will we go so far.""Never again will we go so far," he said.
He said, "Never again will we go so far"; we nonetheless went on.
He said, "Never again will we go so far": those very words.
If you have a parenthetical reference at the end of a quotation, precede it with quotation marks and follow it with the punctuation:
"...government of the people, by the people, and for the people, shall not perish..." (p.76).Americans fought bitterly so that "government of the people, by the people, and for the people, shall not perish" (p.76); yet seldom....
The string of three or four dots that appears in the examples above is called an ellipsis, and it indicates that the sentence being cited has not been given in full. Ellipses are very useful but must be handled intelligently. Be careful not to pare away so much of the original text that the quotation becomes unfaithful or nonsensical. An ellipsis with three dots (...) indicates that only the beginning or middle of the sentence has been omitted. An ellipsis with three dots followed by a period (....) means that the remainder of the sentence, up to its closing period, has been left out.
If you intend to quote more than one sentence, or if a single quoted sentence takes up more than three lines, set the quotation as a separate block. Insert one blank line in double-space format, two blank lines in single spacing. Then type the block quotation in single-space format with each new line indented. Do not enclose block quotations in quotation marks (" "). Follow the quotation with a footnote or page reference as you would an ordinary quotation. Remember that all the standards of good quotation apply to block quotations, particularly the caution against padding out your text with irrelevant material.
Square brackets [these] are not to be confused with parentheses (these) or braces {these}. Square brackets are used to introduce editorial comment into quoted material or to correct for ambiguity caused by removing a quotation from its original context:
I hope to see you all next month in Paris [Texas].Introducing the word sic (Latin for "thus") in square brackets signals that your quotation contains some error or questionable expression the reader might notice:
The idea never ocured [sic] to me.Some writers prefer not to use [sic], since it can reflect an attitude of superiority or class bias. You are best off using [sic] only to identify mistakes made by educated sources who should know better. If you decide not to employ the [sic] convention, you should inform your readers of your practice in the first footnote or in a separate statement at the beginning or end of the paper.
An apostrophe (') indicates that one or more letters have been omitted from a word in a contraction ("do not" becomes "don't"; "he is" becomes "he's"). Apostrophes also occur in possessives ("the wrath of Guido" becomes "Guido's wrath"). Generally you need worry only about possessives, since contractions are not acceptable in formal prose; but if you do have occasion to use the contraction "it's" (for "it is"), do not confuse it with the possessive form of the pronoun, "its" (no apostrophe). Never leave out the apostrophe in a possessive noun (not "Herbs dog" but "Herb's dog"). In making plural nouns possessive use the apostrophe alone:
The soldiers' cries gave away their position.In making possessive a proper noun that already ends in "s," you may either use the apostrophe or an apostrophe and an "s," thus:
This is an important feature of Yeats' poetry.This is an important feature of Yeats's poetry.
Reserve the exclamation point for cases of genuine surprise or perplexity, which will come along very rarely. If you simply wish to emphasize a statement, set it off between dashes or (if really necessary) underline it.
See also Purdue handouts on commas ( Using Commas, Commas After Introductions, Comma Splices and Fused Sentences) and the accompanying exercises ( Punctuation - Commas - #1, Punctuation - Commas #2, Commas - #3, Commas - #4); also look at their handouts on apostrophes and hyphens.
Copyright 1996 Yale University. Revised on Monday, May 20, 1996