Punctuation is one component of writing that people seldom think about or notice -- except when it is wrong. At their worst, misused punctuation marks -- commas, semicolons, quotation marks, and the rest -- may muddle the meaning of your sentences, leaving your reader confused and frustrated. Even less egregious errors -- say, a missing or misplaced apostrophe -- can give your written work an appearance of carelessness and lack of attention.

Purdue University's Online Writing Lab has an excellent section on punctuation of all kinds. It would be a good investment of time to refresh your memory with the explanations and practice exercises found on that site. Here, though, are brief discussions of some of the most common punctuation errors.

Quotation Marks | Apostrophes | Semicolons | Commas
Dash Versus Hyphen | Punctuation with Citations


Quotation Marks

Quotation marks are required whenever you are giving the exact words spoken or written by another person. In American English, double quotation marks are used for indicating quotations. Single quotation marks indicate a quote within a quote:

Prof. McArdle said, "The briefs will be due on Tuesday."

Loucas said, "Prof. McArdle said, 'The briefs will be due on Tuesday.'"

(For those of you familiar with British English conventions, this is a change in style.)

The rules for using other punctuation with quotation marks are fairly straightforward. If you are introducing a quote with a phrase such as "He said," "The record states," or "As Justice Scalia wrote," you must use a comma before the quotation marks:

The defense attorney shouted, "I object to that question!"

If you want to introduce a quote with an independent clause (a phrase that could stand alone as its own sentence), you must use a colon before the quotation marks:

The defense attorney raised an objection: "That question is not relevant!"

If, however, you are integrating quoted material within your own sentence, you do not need any introductory punctuation:

Evelyn described her father as a "stubborn old man."

You must also be careful about the placement of other punctuation marks at the end of quotations. Commas and periods always go inside quotation marks:

Lou said, "This class is way too noisy."

"This class is way too noisy," said Lou.

Question marks and exclamation points go inside the quotation marks if they are part of the original quotation:

The security guard asked, "Whose car is this?"

but remain outside the quotation marks if they are part of your own sentence:

Did the nurse say, "Dr. Adler will be coming soon"?

(In this case, the nurse is not asking the question; the writer of the sentence is.)

Semicolons and colons at the end of a quotation should be placed outside the quotation marks:

A certain novel begins with the words, "Call me Ishmael": do you know which novel it is?



The two main functions of the apostrophe are to form the possessive case of nouns (indicating ownership) and to indicate a missing letter or letters in a contraction.


When forming the possessive of a singular subject, 's is generally needed:

The student's locker was filled with textbooks.

Margie's bagels are delicious.

If a singular noun ends in s, you should still use 's to form the possessive:

Luis's car is parked on Main Street.

Her boss's office is very large.

However, some writers use an apostrophe alone when the noun is long and contains multiple s sounds. This is not incorrect:

Officer Gonzales' gun was stolen.

When forming the possessive of plural nouns, you should add only an apostrophe if the noun ends in s:

The students' grades were posted on the board.

But the occasional plural nouns that don't end in s need 's to form the possessive:

The children's center opens at 9 a.m.

In two unusual cases, 's is used to form a plural noun. This occurs when you want the plural form of a single letter or of a word referred to as the word itself, as in the following examples:

Patrick got straight A's throughout four years of college.

This brief contains too many whether's.

Never use an apostrophe to form the plural of a proper name:

The Blochs came over for dinner.


The apostrophe is also used to replace missing letters in a contraction. For example, in the following sentence:

The clerk said the office wouldn't be open on Saturday.

"wouldn't" is a contraction for "would not" -- the apostrophe replaces the missing o.

Similarly, in the sentence:

We're tired from studying too much.

"we're" stands for "we are," so the apostrophe replaces the missing a.

Your/You're & Its/It's

The two instances that cause the most confusion -- and the most mistakes -- in apostrophe usage are your/you're and its/it's.

Remember the contraction rule, and your choice should be clear. "You're" stands for "you are," while "your" is the possessive form of "you":

"You're the top student in your class," said the dean.

Likewise, "it's" stands for "it is" or "it has," while "its" is the possessive form of "it":

It's time for the orchestra to begin its rehearsal.

If you are confused about which word to use in a sentence, pause and ask yourself which meaning you want -- a contraction or a possessive noun.



A semicolon can be used to connect two independent clauses that are closely linked in meaning:

The professor began class at exactly 10 o'clock; students who arrived late missed some of the lecture.

In this example, the two clauses could stand alone as separate sentences, but joining them with a semicolon stresses the relationship between them. Using a comma alone to connect these clauses would not be sufficient and would create a run-on sentence.

A semicolon would also be used to connect independent clauses when a transitional word or phrase is used, such as:

The small airplane had a smooth flight; however, a sudden gust of wind made its landing a little rough.



Comma placement can dramatically alter the meaning of a sentence. Comma placement determines the grammatical, and therefore logical, structure of the sentence.

When should I use commas?

  1. Use commas to separate independent clauses when they are joined by coordinating conjunctions: and, but, for, or, nor, yet.
    Example: Tuparo began his new job, and Burstyn made changes to the personnel policy. (Note that this could have been expressed in two sentences: Tuparo began his new job. Burstyn made changes to the personnel policy.)

  2. Introductory expressions should be followed by a comma.
    a. After leaving Weber and Orange, Tuparo took a job at LSRA.
    b. Therefore, he did not make a counteroffer.

  3. Use commas to separate three or more words, phrases, or clauses written in a series.
    a. I bought eggs, milk, and cheese at the store.
    b. Yesterday I read a book, took a walk, and wrote a paper.

  4. Use a pair of commas in the middle of a sentence to set off clauses, phrases, and words that are not essential to the meaning of the sentence.
    Example: His neighbor, with whom he had had several serious disagreements, removed a section of the fence. (Note that the clause "with whom he had had several serious disagreements" is not essential to the meaning of the sentence. One way to check this is to see if we could rewrite the sentence to make two complete sentences. Example: His neighbor removed a section of the fence. They had had several serious disagreements.)

When should I not use commas?

  1. Don't use commas to set off parts of the sentence that are essential to the meaning, such as clauses beginning with "that". Examples:
    a. The book that I borrowed from you is excellent.
    b. The last person who saw the victim alive claimed to have seen nothing unusual.

  2. Tip: "Which" is generally used with a comma, "that" without. Examples:
    a. Mr. O'Malley's apartment, which is on the seventh floor, is unsuitable for someone with mobility problems. (Non-essential to the meaning)
    b. The bill that Ms. Perez received contained several errors. (Essential to the meaning)

  3. Commas should not separate subjects from their corresponding verbs. Example: The new chief operating officer, changed the company's personnel and benefits policies. (incorrect)

  4. Commas should not separate verbs from their objects. Example: The new chief operating officer changed, the company's personnel and benefits policies. (incorrect)

  5. Commas should not split a double (or compound) predicate. Example: Tuparo finished his Masters, and got a new job. (incorrect)

When in doubt, use a comma if you think your reader may be confused about the meaning.


Dash Versus Hyphen

Rule of thumb, dashes separate, hyphens connect. When typing on word, a dash is made up of two hyphens (– –). Newer versions of word will generally connect them into one dash (—).

  1. Dashes offer separation but with added drama. Example: Everyone in the group left the scene-even her brother. (correct)

  2. Dashes can also be used to set off a clause, parenthetical expression, or list. Examples:
    a. His neighbor-with whom he had had several serious disagreements-removed a section of the fence. (you could use commas here instead, but dashes change the emphasis)
    b. Our clients-Singh, Lafrance, and Ivanoff-have sent us the documents we requested. (you could use commas here but it would be more confusing to the reader)

  3. Use a hyphen to connect two parts of a compound noun. Examples: U-turn, stand-in.

  4. A hyphen is used to join two parts of a hyphenated adjective. Examples: once-in-a-lifetime opportunity, state-run clinic. (This often makes the meaning clearer. Consider the possible meaning of the following: working class president, dirty blonde hair, versus working-class president, dirty-blonde hair.)

  5. Many prefixes are hyphenated, especially if there may be awkwardness or confusion with the spelling. Example: ex-husband, pre-1968, semi-integrated, non-nuclear. (Some works are acceptable hyphenated and not. Example: pre-war, prewar.)

For More Information:

Purdue Owl Writing Lab (OWL), "Brief Overview of Punctuation," 2012. (link)

Search for your punctuation question at Grammar Girl. (link)


Punctuation with Citations

Citations are governed by a number of rules that are beyond the scope of this discussion. For guidance in proper citation format, you should consult the Bluebook, our bluebook page, or the Cornell and Lexis-Nexis sites devoted to citation style.

However, here are a few basic rules regarding punctuation placement with citations. A citation that appears after a complete sentence should be treated as a complete sentence itself, beginning with a capital letter and ending with a period. This holds true whether the citation is a long or short form. If a cite is given in the middle of a sentence, it must be set off by commas. Notice the punctuation of the citations in the following example:

In New York, the rule is well settled that an advertisement is merely an invitation to enter into negotiations, and is not an offer that may be turned into a contract by a person who communicates an intention to purchase the advertised item. Geismar v. Abraham & Strauss, 439 N.Y.S.2d 1005 (Dist. Ct. Suffolk Co. 1981); Lovett v. Frederick Loeser & Co., 207 N.Y.S.753 (Manhattan Mun. Ct. 1924). The only general test is the inquiry whether the facts show that some performance was promised in positive terms in return for something requested. Lovett, 207 N.Y.S.2d at 755. However, a purchaser may not make a valid contract by mere acceptance of a "proposition," Schenectady Stove Co., 101 N.Y. at 48, nor does the purchaser have the right to select an item which the seller does not have in stock or is not willing to sell at a reduced price. Lovett, 207 N.Y.S. at 757.

As illustrated in the first citation, when two or more cases are named, they must be separated by a semicolon. Also, be careful not to italicize the comma following the name of the case.