Types of Punctuation Marks & Uses

The end of a complete sentence should be marked by a period, a question mark, or an exclamation point. If a sentence is not complete and it is terminated by a period, we have a sentence fragment as in the sentence below.

• Incorrect: You can use any resources. To complete your take-home exam.

• Correct: You can use any resources to complete your take-home exam.

End of Sentence

A period is used to signal the end of a complete sentence.

• Correct: This is the best paper I've ever written.

A period is also used at the end of an indirect question.

• Correct: The teacher asked us if we understood the assignment.

Polite requests can be followed either by a period or by a question mark.

• Correct: Will you please mail this letter for me.

• Correct: Will you please mail this letter for me?

Abbreviations

A period should be placed after every part of the abbreviation:

• A.D.

• Dr. Watson

• a.m. (am is also possible)

• Ave.

However, very common abbreviations and units of measure don't take periods:

• mph

• mp3

• rpm

• mpg

Academic degrees can be written with or without periods:

• DDS

• EdD

• M.S.

• B.A.

Lower case abbreviations are usually written with periods but not when they are a unit of measurement: 

• i.e.

• etc.

• ex.

• kg

• mph

Government agencies and international organizations are written without periods:

• FBI

• UNESCO

• UN

• NATO

• UNICEF

• EU

Direct questions are followed by a question mark.

• Correct: The teacher asked, "Do you understand the assignment?"

Exclamatory sentences should be followed by an exclamation point.

• Correct: Wow! That's incredible!

Most often commas are used to separate items in a series or to set off introductory phrases. This section outlines the most common comma uses, but understand there are more uses for commas that go beyond this section. 

Consider the following sentence:

• Incorrect: While you were watching your favorite show I managed to finish the first assignment.

  • Correct: While you were watching your favorite show, I managed to finish the first assignment.

In the sentence above, the adverbial clause "while you were watching your favorite show" needs to be set off by a comma.

Introductory Words and Clauses

A comma is used to separate introductory words (besides, however, furthermore, therefore) and introductory phrases and clauses.

• Correct: I need to spend some time preparing for this test. Besides, it's such an important test.

A comma is used to separate introductory participial phrases, adverbial clauses, and prepositional clauses.

• Correct: Waiting for the storm to stop, I was anxiously looking out the window.

Appositives and Parenthetical Expressions

Commas are also used to set off appositives and parenthetical expressions.

An "appositive" is a word that follows a noun and explains it.

• Correct: Anderson Cooper, a reporter, gained his first experience and eventual popularity by covering war stories.

Parenthetical expressions also explain or clarify the sentence. Some of the more common expressions are of course, I believe, after all, by the way, in my opinion, for example, to tell the truth.

In the following sentence, "I believe" is a parenthetical expression.

• Correct: The Big Bang Theory, I believe, provides a very interesting explanation of the origin of the universe.

And in this sentence, "I believe" is not a parenthetical expression.

• Correct: I believe that The Big Bang Theory provides a very interesting explanation of the origin of the universe.

Such words as however, moreover, nevertheless, otherwise, or therefore often appear parenthetically.

• Correct: I realize, however, that this theory may be flawed.

Non-defining clauses provide additional information about the noun they modify. These clauses are typically separated by commas.

• Correct: Anderson Cooper, who is Gloria Vanderbilt's son, is a reporter.

• Correct: Thinking back, I realize now what kind of mistake I made.

Compound Sentences

When joining two complete sentences, use a comma before a coordinating conjunction (for, and, nor, but, or, yet, so).

• Correct: Laura developed the film, and Jason printed the pictures.

Dates, Addresses, Geographical Names

• Correct: Our last class reunion was on August 5, 1999, in Chicago, Illinois.

When only month and date are given, no comma is necessary.

• Correct: We are meeting on August 5.

Lists

When listing three or more items (either words, phrases, or clauses) in a series, use commas to separate them. There are different views on whether a comma is needed before "and." Some grammarians have stated that it is not needed, and some have said that adding a comma before "and" (called "the Oxford comma") prevents confusion in a sentence. Whichever rule you decide to go by, make sure you are consistent throughout your writing whenever there are series of items joined by and.

• Correct: Laura showed Jason how to cut the negatives, dust the lens and counters, and change the ink ribbons in the printers.

• Correct: Laura showed Jason how to cut the negatives, dust the lens and counters and change the ink ribbons in the printers.

Adjectives

When two adjectives separately modify the same noun and can be inverted and connected with "and," use a comma between them.

• Correct: Rude, unruly customers always seem to be the first ones in line.

Semicolons join ideas that are related and equal in grammatical structure.

• Incorrect: This assignment is extra credit only; but we still need to hand it in.

Even though the two clauses in the sentence above are related, we cannot use a semicolon there because the clauses are joined by the coordinating conjunction "but." We can use either the semicolon there or the conjunction, but not both.

• Correct: This assignment is extra credit only, but we still need to hand it in.

• Correct: This assignment is extra credit only; however, we still need to hand it in.

Semicolons with Independent Clauses

Use a semicolon to join two related independent clauses in place of a comma and a coordinating conjunction (for, and, nor, but, or, yet, so). Make sure when you use the semicolon that the connection between the two independent clauses is clear without the coordinating conjunction.

• Correct: John finished all his homework, but Kathleen did not finish hers.

You can replace the comma and coordinating conjunction (but) with a semicolon since the connection between the two independent clauses is clear without the coordinating conjunction.

• Correct: John finished all his homework; Kathleen did not finish hers.

Semicolons should not be used between a dependent clause and an independent clause.

• Incorrect: Although Nate is a kind employee; that new guy is not.

  • Correct: Although Nate is a kind employee, that new guy is not.

Semicolons with Conjunctive Adverbs and Transitional Expressions

Use a semicolon to replace a period between related sentences when the second sentence starts with either a conjunctive adverb or a transitional expression, such as: for example, for instance, that is, besides, accordingly, furthermore, otherwise, however, thus, therefore.

Conjunctive Adverb:

• Correct: Kathleen worked for many hours on all her homework; nevertheless, she was unable to finish all of it.

• Correct: Harvey is a good driver; moreover, he is a friendly one.

Transitional Expression:

• Correct: Tony finished reading three novels this week; in contrast, Joan finished only one novel.

Semicolons Used to Replace Commas

Use semicolons to replace commas when individual items in a series are long or contain commas. Use a semicolon instead of a comma to separate the items.

• Confusing: Angela loves many breeds of dogs including small dogs, such as terriers and beagles, medium dogs, such as border collies and cocker spaniels, and large dogs, such as Great Danes and mastiffs.

Since each of the elements in the list in the sentence above is complicated and has commas, it is difficult to figure out where one element ends and the next begins. Using semicolons between the lengthy elements helps the reader understand the separation, as shown in the example below:

• Preferred: Angela loves many breeds of dogs including small dogs, such as terriers and beagles; medium dogs, such as border collies and cocker spaniels; and large dogs, such as Great Danes and mastiffs.

Sometimes it can be confusing deciding when to use a colon or a semicolon. The colon is used to provide an example or more detailed information in the sentence.

• Incorrect: A teacher should be gifted or skilled in such areas as: patience, self-reflection, and humor.

In the sentence above, no colon is needed after the phrase in such areas as.

• Correct: A teacher should be gifted or skilled in such areas as patience, self-reflection, and humor.

The colon is used after the expressions "the following" or "as follows" but not after "for example," "including," "such as," or "that is."

• Correct: You can utilize the following resources for your paper: encyclopedias, atlases, and dictionaries.

The colon is used after an independent clause or a dependent clause. It may link two separate clauses or phrases by indicating a step forward from the first clause to the second.

• Correct: I think I know why I am not feeling well today: I spent too much time in the sun yesterday.

The colon is used between two independent clauses when the second modifies the first

• Correct: These laptops are a great buy: they are lightweight, powerful, and inexpensive.

The colon is used to indicate a quotation that is formally announced

• Correct: An old Irish proverb says: "There are two beginnings to every year."

The colon is used before a list, an explanation, or a definition that is preceded by a clause that can stand alone

• Correct: I was able to fit everything in my laptop bag: laptop, mouse, network cable, power supply, and a notebook.

The colon is used after a salutation in formal correspondence

• Correct: Dear Members of the Hiring Committee:
  Thank you for considering my application.

The colon is used between the hour and minute in time

• Correct: 5:30 a.m.

The colon is used to introduce a long formal quotation

• Correct: The author concludes by emphasizing the relevance of wikis in education:

Regardless of how educators feel about the potential of wikis, and I can understand the hesitancy many teachers feel, one thing remains certain. The collaborative environment that wikis facilitate can teach students much about how to work with others, how to create community, and how to operate in a world where creation of knowledge and information is more and more becoming a group effort. (Richardson 74)

Remember: Indent long quotations (also called block quotes) half an inch.

Finally, the colon is used between volumes and page numbers or chapters and verses

• Correct: Chicago 10:25-28

Parentheses are used to explain the statement or provide explanatory information in the sentence.

• Incorrect: The teacher told us: what a great reminder! to include the list of works cited with our essays.

  • Correct: The teacher told us (what a great reminder!) to include the list of works cited with our essays.

• Incorrect: The Classroom Performance System - CPS - is a student response system developed by eInstruction.

  • Correct: The Classroom Performance System (CPS) is a student response system developed by eInstruction.

The two sentences above require the use of parentheses to enclose additional or explanatory information in the sentence.

Parentheses ( ) usually indicate a full interruption in thought.

• Correct: He wanted to go home, but couldn't (too much to do).

They can also be used to substitute for the word "or" in certain types of sentences. For instance:

• Correct: What part(s) do you want?

Parentheses are frequently used to introduce abbreviations, especially in technical and scientific writing.

• Correct: This paper discusses the potential veracity of reports documenting Extra Sensory Perception (ESP) in the United States.

Parentheses are also used in figure captions and with numbers of items in lists.

• Correct: Two steps are needed to complete our project: (1) decide on a website design and (2) choose the hosting service.

• Correct: Figure 2 shows two samples: (a) sample after cooling and (b) sample taken in normal temperatures.

Dashes are primarily used to indicate a pause in thought which offers more detail or emphasizes a point of information.  Dashes can be written as —  or --.

• Correct: I wish I in was Georgia -- Atlanta, that is.

The may also be used to separate an appositive phrase, usually a list, from the rest of the sentence.

• Correct: I had these books — by Tolkien, Bear, and Herbert — renewed because they were overdue.

Brackets [ ] have very specific uses in formal writing; they are used either to insert commentary, missing words, or ellipses within direct quotes.

• Correct: Jones states, "Only five [people out of the original group] were left alive after Stalin's purges."

In this sentence, the person quoting Jones is adding specific information that was not given by the author. Similarly:

Consider the following sentence:

• Correct: Davidson argues, "We can only do so much before [...] we have to give up this futile attempt."

In this sentence, the person is adding ellipses to a quote, indicating that he or she has cut out words between before and we.  The words they have cut out, though, does not change the meaning of the original quote.

Apostrophe errors often occur when the plural form and the possessive form are confused. Additionally, apostrophes also tend to be used incorrectly with years.

• Incorrect: Joneses yard is much bigger than Smith's.

  • Correct: Jones's yard is much bigger than Smith's.

• Incorrect: My brother graduated from NIU in the early 1990's.

  • Correct: My brother graduated from NIU in the early 1990s.

The apostrophe is not strictly a punctuation mark, but more a part of a word to indicate possessive case, contractions, or omitted letters.

Possessives

To see if you need to make a possessive, turn the phrase around and make it an "of the..." phrase. For example:

• the boy's hat = the hat of the boy

• three days' journey = journey of three days

If the noun after "of" is a building, an object, or a piece of furniture, then no apostrophe is needed!

• room of the hotel = hotel room

• door of the car = car door

• leg of the table = table leg

Once you've determined whether you need to make a possessive, follow these rules to create one.

Rule #1: Add 's to the singular form of the word (even if it ends in -s):

• the owner's car

• James's hat (James' hat is also acceptable.)

Rule #2: Add 's to the plural forms that do not end in -s:

• the children's game

• the geese's honking

Rule #3: Add ' to the end of plural nouns that end in -s:

• two cats' toys

• three friends' letters

• the countries' laws

Rule #4: Add 's to the end of compound words:

• my brother-in-law's money

Rule #5: Add 's to the last noun to show joint possession of an object:

• Todd and Anne's apartment

Contractions

A contraction is one word that is formed by combing two words. As the two words are combined, a letter is (letters are) dropped and an apostrophe is added in its place. Usually, a pronoun and a verb are used when forming contractions.

The following is a list of common contractions:

• 'd when contracting would or had (he'd)

• 'm when contracting am (I'm)

• 's when contracting is or has (she's)

• 'll when contracting will (I'll)

• 're when contracting are (they're)

• 've when contracting have (we've)

• n't when negating some helping or linking verbs (wasn't, shouldn't)

Correct: They'll complete the assignment by tomorrow.

"Not" is used to form negative contractions with many linking verbs. When making a negative contraction, omit the "o" in "not" and replace it with an apostrophe. The only exception to this rule is "will not," which contracts to form "won't."

• Correct: Don't take my car!

Numbers and Omissions

Numbers can be shortened by adding an apostrophe in place of the omitted number.

• Correct: the class of '07

• Correct: events in the '60s

Be careful using abbreviations in formal writing. In most cases, it is best to spell the numbers out or write them as full numerals.

Plurals of Letters, Words, Numbers, and Signs

An apostrophe and s are also used to form the plural of letters, numbers, signs, and words referring to words.

• Correct: The word Mississippi has many s's.

• Correct: Count incorrectly spelled accent's in your essay.

When Don't You Need an Apostrophe?

With time periods and after numbers

• Incorrect: The 1900's = the years between 1900-1999

  • Correct: The 1900s = the years between 1900-1999

• Incorrect: MP3's = more than one MP3

  • Correct: MP3s = more than one MP3

After symbols:

• Correct: *s = asterisks

• Correct: #s = pounds/numbers

After abbreviations:

• Correct: CDs = compact disks

• Correct: DVDs = digital video (or versatile) disks

With possessive pronouns:

• its, hers, his, theirs, my, mine, ours, yours, whose

A direct quote needs to be enclosed in quotation marks. Consider the following sentence:

• Incorrect: How did you do on your final, my roommate asked.

• Correct: "How did you do on your final?" my roommate asked.

  • Correcting the Problem: Because the above sentence contains a direct quote, it needs to be enclosed in quotation marks.

Single quotes are used to enclose a quotation inside a quotation.

• Correct: "I'm writing a book about the Battle of Gettysburg," the historian said, "and I think it will be important to refer to Lincoln's Gettysburg Address, particularly the part of the speech where he says, 'The world will little note nor long remember what we say here, but it cannot forget what they did here'."

Long Direct Quotations

In a narrative, when dialogue is used, long direct quotations should have quotation marks at the beginning and at the end of each paragraph. Dialogue should begin on a new line each time there is a change in speaker.

In essays, research papers, or reports, when a quotation is more than four lines long, that quotation needs to be indented half an inch, double-spaced, and NOT enclosed in quotation marks. Such long quotations are also called block quotes. Consider the following example:

• Correct: The author concludes by emphasizing the relevance of wikis in education:

Regardless of how educators feel about the potential of wikis, and I can understand the hesitancy many teachers feel, one thing remains certain. The collaborative environment that wikis facilitate can teach students much about how to work with others, how to create community, and how to operate in a world where creation of knowledge and information is more and more becoming a group effort. (Richardson 74)

In American English, double-quotation marks are most commonly used to indicate actual speech or dialogue (as in novels and stories) or to set off direct quotations of text or speech from other sources (as in critical essays and research papers).

• Correct: "Your research papers will be due at the end of the semester," the teacher said. "How long do they have to be?" one student asked. "Roughly ten pages," she replied, "so we'll be focusing on your research skills for much of the course."

• Correct: Here's my favorite quote by George Bernard Shaw: "A life spent making mistakes is not only more honorable, but more useful than a life spent doing nothing."

Direct Quotations

Direct quotations include a person's actual words which need to be enclosed in quotation marks.

Use a comma to introduce a quotation after a standard dialogue tag, a brief introductory phrase, or a dependent clause.

• Correct: The detective said, "I am sure who performed the murder."

• Correct: As D.H. Nachas explains, "The gestures used for greeting others differ greatly from one culture to another."

A direct quotation needs to start with a capital letter, unless it is divided into two or more parts. Then the second part should start with the lower case letter.

• Correct: "Take the time to proofread your essay," the teacher said, "before you hand it in."

Put commas and periods within quotation marks, except when a parenthetical reference follows.

• Correct: He said, "I may forget your name, but I never forget a face."

• Correct: History is stained with blood spilled in the name of "civilization."

• Correct: Mullen, criticizing the apparent inaction, writes, "Donahue's policy was to do nothing" (24).

Place a question mark or exclamation point within closing quotation marks if the punctuation applies to the direct quote itself. Place the punctuation outside the closing quotation marks if the punctuation applies to the whole sentence.

• Correct: "Have you ever taken an online class?" my counselor asked.

• Correct: "Yes, of course!" I answered.

• Correct: Does Dr. Lim always say to her students, "You must work harder"?

Semicolons and colons should always be placed outside the closing quotation marks.

• Correct: The teacher said, "The assignment is due next week"; then he proceeded to explain what we needed to do for this assignment.

• Correct: Williams described the experiment as "a definitive step forward"; other scientists disagreed.

• Correct: Benedetto emphasizes three elements of what she calls her "Olympic journey": family support, personal commitment, and great coaching.

Indirect Quotations

Indirect quotations do not state the speaker's words exactly; rather they indicate the general idea of what was said.

Indirect quotations should not be enclosed in quotation marks.

• Correct: The teacher announced that the assignment would be due next week, and then he proceeded to explain what we needed to do for this assignment.

Titles of Sources in a Container

Another conventional usage of double quotation marks is to set off the titles of short stories, short poems, one-act plays, short films, songs, television episodes, essays, articles, and other short works.  These are found in containers, such as novels, full-length plays, long poems, albums, television series, films, books, magazines and journals, newspapers, and other longer works, which are marked by italics.

• Correct: "Hills Like White Elephants" is a story by Hemingway.

• Correct: "Hush," an episode from the fourth season of Buffy the Vampire Slayer, is considered one of the very best of the whole series, but it's possible that "Restless," from the same season, is better.

• Correct: Lust for Life is a book based on the life of Vincent van Gogh.

Word Definitions

When you are defining a word in a sentence, the word or phrase and the definition is typically included in quotation marks.

• Correct: The word "accept" means "to agree or receive favorably."