Punctuation Rules

Period
Use a period to end a complete sentence. A sentence is a group of words containing a subject and predicate. In British English a period is called a 'full stop'.
Examples:
He went to Detroit last week.
They are going to visit.

Comma
There are a number of different uses for commas in English. Commas are used to:

• Separate a list of items. This is one of the most common uses of a comma. Notice that a comma is included before the conjunction 'and' which comes before the final element of a list.

Examples:
I like reading, listening to music, taking long walks, and visiting with my friends.
They would like books, magazines, DVDs, video cassettes, and other learning materials for their library.

• Separate phrases (clauses). This is especially true after a beginning dependent clause or a long prepositional phrase.

Examples:
In order to qualify for your certificate, you will need to take the TOEFL exam.
Although he wanted to come, he wasn't able to attend the course.

• Separate two independent clauses that are connected by a conjunction such as 'but'.

Examples:
They wanted to purchase a new car, but their financial situation would not allow it.
I'd really enjoy seeing a film this evening, and I'd like to go out for a drink.

• Introduce a direct quote (as opposed to indirect speech i.e. He said he wanted to come ...).

Examples:
The boy said, "My father is often away during the week on business trips."
His doctor replied, "If you don't stop smoking, you run the risk of a heart attack."

• Separate appositives (a noun, or noun phrase) or non-defining relative clauses.

Examples:
Bill Gates, the richest man in the world, comes from Seattle.
My only sister, who is a fantastic tennis player, is in great shape.

 
Question Mark
The question mark is used at the end of a question.
Examples:
Where do you live?
How long have they been studying?
 
Exclamation Point
The exclamation point is used at the end of a sentence to indicate great surprise. It is also used for emphasis when making a point. Be careful not to use an exclamation point too often.
Examples:
That ride was fantastic!
I can't believe he is going to marry her!
 
Semicolon
There are two uses for a semicolon:

• To separate two independent clauses. One or both of the clauses are short and the ideas expressed are usually very similar.

Examples:
He loves studying; He can't get enough of school.
What an incredible situation; it must make you nervous.

• To separate groups of words that are themselves separated by commas.

Examples:
I took a holiday and played golf, which I love; read a lot, which I needed to do; and slept late, which I hadn't done for quite a while.
They plan to study German, for their travels; chemistry, for their work; and literature, for their own enjoyment.

 
Colon
A colon can be used for two purposes:

• To provide additional details and explanation.

Examples:
He had many reasons for joining the club: to get in shape, to make new friends, to lose some weight, and to get out of the house.
She gave notice for the following reasons: bad pay, horrible hours, poor relations with colleagues, and her boss.

• To introduce a direct quote (a comma can also be used in this situation).

Examples:
He announced to his friends: "I'm getting married!"
She cried out: "I never want to see you again!"