How to Use Periods

A period is used to indicate that a sentence is a statement or a command.

• Statement: I completed my homework on time.
• Command: You need to finish your homework before it’s due.

Periods with abbreviations

Periods are used in some abbreviations. When an abbreviation with a period is used at the end of a sentence, don’t use an extra period to end the sentence. 

• Example: I asked her to come at 10 a.m.

Periods with quotation marks

Periods should be placed inside a quote.

• Correct: Morticia said, “The graveyard is very beautiful.”
• Incorrect: Morticia said, “The graveyard is very beautiful”.

Use a comma instead of a period if the end of a quote is not the end of the sentence.

• Correct: “The graveyard is very beautiful,” Morticia said.
• Incorrect: “The graveyard is very beautiful.” Morticia said.

Periods with parentheses

Sometimes parentheses come at the end of a sentence, such as when citing a source of making a side comment. Punctuation should always come after the end of the parentheses.

• Example: The study measured “cooperative play in baby kittens” (Jones 1).
• Example: The art exhibition was a huge success (thanks largely to Gerard’s help).

How to Use Question Marks

Question marks are used at the end of questions. When there is a question mark, there should not also be a period since the question mark is the end punctuation.

Sometimes, a sentence that is a question has some quoted words. The question mark still goes at the end of the sentence:

• Example: Does anyone really know whether "the earth will be impacted by a meteor in the near future"?

If there is a quoted question in a sentence, then the question mark goes inside the quotation marks:

• Example: He asked, “Who is going?”

Sometimes, there is a question about whether a sentence contains a direct question.

• Example: He asked about who is going.

With this phrasing, there is no direct question. It is an indirect question. Question marks should not be used.

Question marks can also be used for rhetorical questions – questions used for persuasion.

• Example: The earth has been gradually warming since the end of the last Ice Age. Are humans really speeding up this warming trend or is it just part of the natural process?

How to Use Exclamation Points

An exclamation point is used to show strong emphasis or importance.

• Example: “Put down the box!” the woman yelled.

Ordinarily, we would use a comma to separate out the words that say who says a quote (a signal tag).  However, a comma is not used next to an exclamation point.

Exclamation points are rarely used in research writing.  When it is used in a direct quote, only one exclamation point is used.  Don’t add additional exclamation points to be more emphatic.

• Correct: Stop!
• Incorrect: Stop!!

Other Punctuation Issues

Comma splices and run-on sentences often confuse a reader. 

Comma Splices

A comma splice is a grammatical error that occurs when a comma is used to incorrectly combine two independent clauses into a single sentence.

Here is an example of a comma splice.

• Incorrect: I climbed up the mountain, the view at the top was breathtaking.

A comma splice can be fixed by separating the two independent clauses into two sentences.

• Correct: I climbed up the mountain. The view at the top was breathtaking.

A comma splice can be fixed by separating the two independent clauses with a semicolon.

• Correct: I climbed up the mountain; the view at the top was breathtaking.

A comma splice can be fixed by separating the two independent clauses with a comma and a coordinating conjunction.

• Correct: I climbed up the mountain, and the view at the top was breathtaking.

Run-on Sentences

A run-on sentence is a grammatical error that occurs when punctuation is missing at the end of a sentence, causing it to fuse with the sentence that comes after it.

Here is an example of a run-on sentence.

• Incorrect: I climbed up the mountain the view at the top was breathtaking.

A run-on sentence can be fixed by separating the two independent clauses into two sentences.

• Correct: I climbed up the mountain. The view at the top was breathtaking.

A run-on sentence can be fixed by separating the two independent clauses with a semicolon.

• Correct: I climbed up the mountain; the view at the top was breathtaking.

A run-on sentence can be fixed by separating the two independent clauses with a comma and a coordinating conjunction.

• Correct: I climbed up the mountain, and the view at the top was breathtaking.