Period — Meaning and Uses
What is a period?
A period marks the end of a sentence and separates elements within the citation of a source. Also known as a full stop, this punctuation mark ends a declarative sentence, which are statements that communicate information.
When to use a period
Use a period with the following:
Sentences: Place a period at the end of sentences that are statements, instructions, demands, or indirect questions.
Statement: I sent my brother a text message.
Instruction: Rinse the dishes before putting them in the dishwasher.
Demand: Stay off the grass.
Indirect Question: The teacher asked Eric why he was late to class.
Quotations: When punctuating a quotation, place the period after the last word but before the closing quotation mark. This only applies to quotations that do not contain a parenthetical citation.
Ian commented, "Thank you for all of your help today."
Citations: If a sentence ends with information that needs a parenthetical citation (direct quotation, summary, paraphrase), place the period after the citation.
"Not all those who wander are lost" (Tolkien).
Researchers found that the treatment worked 25% of the time (Jones).
Reference List: Consult a style guide about the appropriate places to use periods in reference lists. APA, Chicago Manual of Style, and MLA all have different rules.
Hemingway, Ernest. The Old Man and the Sea. New York: Simon & Schuster, 1952.
Period inside or outside parentheses
When a complete independent clause is enclosed within parentheses, place the period before the closing parenthesis.
Wendy appreciated all of the kind words. (They motivated her to keep pursuing her goal.)
When a word, phrase, or dependent clause is enclosed within parentheses, place the period after the closing parenthesis.
Oliver's library mainly contained three genres (classical, mythological, and philosophical).
Parentheses cannot enclose part of one sentence with another complete sentence. Instead, separate the statements into two sets of parentheses, rewrite the parenthetical information into one phrase, or drop one set of parentheses.
Incorrect: Henry only needed to buy a few more things (soda, chips, and salsa. He wasn't sure he'd need anything else for the party.).
Correct: Henry only needed to buy a few more things (soda, chips, and salsa). (He wasn't sure he'd need anything else for the party.)
Correct: Henry only needed to buy a few more things (soda, chips, and salsa; he wasn't sure he'd need anything else for the party).
Correct: Henry only needed to buy a few more things (soda, chips, and salsa). He wasn't sure he'd need anything else for the party.
Periods with abbreviations and acronyms
Use periods with abbreviations that shorten a word or group of words.
Washington, D.C.
10 a.m.
Dr. Lopez
When a sentence ends with an abbreviation, the final period in the abbreviation also acts as the ending punctuation.
We will get to the park by 10 a.m.
If an acronym is spoken as a word, like NATO, NASA, and SCUBA, do not use periods between the letters.