Definition: a punctuation mark (.) used at the end of a sentence or an abbreviation.
Note: Do not rely on grammar or spelling checkers to identify missing or misused punctuation. Although a checker may flag possibly missing or incorrect marks, it cannot do much else. While I still recommend using these AI checkers while you’re writing, I insist that you also trust a qualified human being to copyedit any work that you are working toward publishing.
The period, arguably the most common punctuation mark, has three uses: to end a sentence, to separate letters in an abbreviation, and to indicate a typographic break.
To end a sentence:
Note: Sentences can also be ended with an exclamation point or a question mark.
Use a period at the end of a statement/declarative sentence.
- e.g. The eagle flies high in the sky.
- e.g. We’re going to Mexico on vacation.
Use a period at the end of a mild command/imperative sentence.
- e.g. Clean your room.
- e.g. Be kind to others.
If the imperative sentence is also an exclamation, use an exclamation point instead [see Exclamation Point (coming soon)].
Use a period at the end of an indirect question.
- e.g. John asked Mary if she would go to the movies with him.
- e.g. I asked my friend for advice.
Unlike a direct question, an indirect question uses the wording and subject-verb order of a statement: the client asked why the bread was out of stock [not why was the bread out of stock].
It is possible (though not common) to use a period at the end of a rhetorical question.
- e.g. May I suggest that you read the introduction before proceeding.
Rhetorical questions can also end with a question mark or an exclamation point.
It is not common to use periods within a list, however, if a complete sentence follows at least one item in the list, put periods after all items.
- e.g. Define the following:
- mammal. Give an example.
Use a period after a person’s initials (unless the current style dictates otherwise). Have either a space after each period or no spaces between two or more initials, depending on the style you are using.
- e.g. Michael T. Smith
- e.g. J. R. Doe or J.R. Doe
Use a period after traditional abbreviations of state and province names but not after the postal service abbreviations of them. In some cases, you can use periods between and after the letter of province/territory abbreviations (not in post).
- e.g. Calif. but CA
- e.g. Brit. Columbia but BC or B.C.
Use a period and no space in other common abbreviations. Depending on the style and/or dictionary, these abbreviations may not use periods at all.
- e.g. Ph.D. or PhD
- e.g. Mrs. or Mrs
- e.g. Mr. or Mr
- e.g. Dr. or Dr
- e.g. a.m. / p.m. or AM / PM
- e.g. i.e.
- e.g. Jan.
A period at the end of an abbreviation may be followed by any other punctuation mark aside from another period.
- e.g. Maria got her Ph.D., then went to work as a biochemist.
- e.g. Hank worked for Blackwood Ltd.
- e.g. Cousin Steve quit his job at Javier Marketing Inc.; Uncle Thomas moved to Germany.
Note: omit periods from these abbreviations
- The initials of a well-known person: JFK, FDR, OBL
- The initials of an organization, corporation, or government agency: CBC, RCMP, CIA
- A well-known position within an organization: CEO, CFO, COO
- A postal abbreviation (in post or in a company name): Toronto, ON; Calgary, AB; BC Ferries
- An acronym, a pronounceable word formed from initials: UNESCO, NAFTA, NATO
Use a period after numbers (or letters) in a displayed list:
Do not use a period following displayed headings. If the headings are complete sentences, use other punctuation.
Use a period (if it is in the style) in references to figure and table numbers [see also Hyphen (coming soon)].
- e.g. See Figure 3.6.
- e.g. In section 1.2, we…
With Other Punctuation:
A period goes inside an end quotation mark.
- e.g. As Ronald Reagan said, “It’s the economy, stupid.”
Do not use a period where there is an exclamation point or a question mark.
- e.g. Grayson asked, “When are we going to Disneyland?”
- e.g. “Don’t go!” Jason cried.
- e.g. Chomsky, N. Who Rules the World? New York: Metropolitan Books, Henry Holt and Company, 2016.
A period may go either inside or outside parentheses, depending on what is enclosed within them. If the enclosure is an independent sentence, it takes its own period. If the enclosure is not an independent sentence, the period goes after the close parenthesis.
- e.g. I finally finished the blanket this morning. (I’ve been working on it for a whole year.)
- e.g. I went to the movie theatre last week (and ate a lot of buttered popcorn).
A period (or comma) usually goes inside a single quotation mark; with philosophical terms, it occasionally goes outside.
- e.g. Define the concept of ‘being’.
- e.g. “When you call me ‘stewardess,’ it sounds old-fashioned,” Mary said.
In British style, since single quotes are used instead of double quotes, so spacing is less of an issue. Therefore, periods and commas can go outside of quotations.
- e.g. Julio Cortázar wrote many short stories, including ‘La noche boca arriba’, ‘Casa tomada’, and ‘Babas del diablo’.
Use a period with ellipsis points in verbatim attribution.
- e.g. “She should have died hereafter…. Out, out brief candle!”
In MLA format, use a period after an ellipse if the sentence ends.
- e.g. In The Strange Case of Dr. Jekyll and Mr. Hyde, Jekyll notes, “The child of Hell had nothing human […]. Edward Hyde, alone in the ranks of mankind, was pure evil.”
For further information, see my other Punctuation articles:
Aaron, J.E. & Morrison, A. The Little, Brown Compact Handbook, 5th Canadian ed. Pearson, 2013, chap 5
Judd, K. Copyediting, A Practical Guide, 3rd ed. California, CA: Crisp Learning, 2001, chap 4