Periods, question marks, and exclamation marks function similarly to other punctuation marks to clarify writing for readers. Periods, question marks, and exclamation marks perform seven basic functions in written English.
Periods, Question Marks, and Exclamation Marks to End Sentences
1. Use periods to end most declarative and some imperative sentences. Declarative sentences are statements. Imperative sentences make direct commands, express requests, and grant or deny permission. For example:
- The puppy is chewing his rawhide.
- Flowers smell lovely.
- Please wash your hands.
Use question marks to end interrogative sentences. Interrogative sentences are questions. For example:
- Is this sentence a question?
- Do you have questions about punctuation marks?
- Where is the puppy?
Use exclamation marks to end sentences including imperative and declarative sentences that convey strong emotion. For example:
- A tornado is heading for our town!
- Don’t pinch the baby!
- Save the puppy from that mean dog!
Periods with Abbreviations
2. Use periods with most abbreviations. For example:
- Mrs. Smith
- 8:45 a.m.
Do not use periods with state or organization abbreviations. For example:
- IL (Illinois)
- NY (New York)
- NASA (National Aeronautics and Space Administration)
Use only one period at the end of a sentence when the last word of the sentence is an abbreviation containing periods. For example:
- Workers must arrive at their desks by 9:00 a.m.
- My family is from the U.S.
- His brother is William J. Smith, Jr.
Periods as Decimal Points
3. Use periods as decimal points to separate integrals from fractional parts of numbers. For example:
Periods with Poetry and Play Citations
4. Use periods to separate elements in poetry and play citations. Place periods between books and lines of poems; acts and scenes of prose plays; and acts, scenes, and lines of verse plays. For example:
- The Inferno 1.13-27 (book.lines)
- For Whom the Seagulls Fly 2.4 (act.scene)
- Hamlet, Prince of Denmark 2.2.1296 (act.scene.line)
Periods with Electronic File Names and Internet Addresses
5. Use periods to separate computer file names with computer file extensions. For example:
Also use periods to separate elements of Internet addresses. For example:
Question Marks with Uncertain Dates and Numbers
6. Use question marks enclosed in parentheses to indicate uncertain dates and numbers. For example:
- Experts believe that Jesus was born in November 5 (?) BCE.
- Born in 1564 (?), William Shakespeare was baptized on April 26.
- Joan of Arc died when she was 19 (?) years old.
Exclamation Marks with Emphatic Interjections
7. Use exclamation marks with emphatic interjections that are not part of the grammatical structure of the main clause. For example:
- Help! The kitchen is on fire!
- Run! The movie is about to begin.
- Mom! The kitty stole my sock again.
For more information on the use of periods, question marks, and exclamation marks within quotation marks, please see The Use of Quotation Marks in Written English.
The accompanying printable reference sheet of the rules for using colons in English is available for download at The Use of Periods, Question Marks, and Exclamation Marks in Written English Reference Sheet.