A period is used to terminate most types of sentences, including declarative, imperative, and conditional sentences, as well as indirect questions. Additionally, periods are used in combination with other punctuation marks, such as parentheses and quotation marks.
Use a period to terminate sentences
1. Declarative sentences make a general statement about something.
- My birthday is in January.
- Your mother wears combat boots.
- The rain in Spain falls mainly on the plain.
2. Imperative sentences give a command.
- Go to the end of the street and turn right.
- Take two aspirin and call me in the morning.
- Please put the book back on the shelf.
3. In conditional sentences; if a specific condition is met, a certain result will follow.
- If you lie down with dogs, you’ll get up with fleas.
- Once I get back from vacation, I will start my new job.
- If it rains tomorrow, the game will be canceled.
Use a period to terminate an indirect question
An indirect question is a declarative sentence that expresses uncertainty or indecision. Similar to a direct question, it demands a reply, but it is expressed as a declaration and does not have the formality of a question. Resist the temptation to use a question mark to end an indirect question. Use a period instead.
- I just wanted to know if you are attending the meeting tonight.
- The teacher asked us why Jim had left the classroom early.
- I was wondering when my dinner will be ready.
Note: The indirect questions above can be rewritten as direct questions as follows:
- Are you attending the meeting tonight?
- The teacher asked us, “Why did Jim leave the classroom early?”
- When will my dinner be ready?
Periods used with abbreviations
We use periods to indicate when a word has been abbreviated. An abbreviated word has had some of its letters omitted. A period always appears immediately after the last letter of the abbreviated word. In addition to standard word abbreviations, there are several subcategories of abbreviations, such as initials, formal titles, acronyms, and initialisms. We will define those subcategories further down the page.
1. Use a period at the end of a standard word abbreviation in a sentence.
- Use 2 tsp. vanilla extract in the recipe.
- Her home address is 1542 Copperhead Rd., Lizard Lick, N.C.
- Please cont. to pg. 19 for further instructions.
2. If an abbreviation appears at the end of a sentence, it is not necessary to add another period to terminate the sentence. The period at the end of the abbreviation acts as the terminal point.
- Please wake me up tomorrow morning at 6 a.m.
- The refugees will need food, clothing, shelter, etc.
- Steve Jobs and Steven Wozniak are the founders of Apple Computer, Inc.
3. If an abbreviation appears at the end of a direct question or an exclamatory sentence, add a question mark or exclamation mark directly after the abbreviation with no space.
- Have you ever been to Washington, D.C.?
- Next week I’m being audited by the I.R.S.!
4. Initials are a type of abbreviation (of people’s names) formed by using the first letter of each part of the name (first, middle, last). Mark each initial with a period.
- John F. Kennedy was the 35th president of the United States.
- H.G. Wells is one of my favorite authors.
- J.R.R. Tolkien wrote The Hobbit and Lord of the Rings.
Note: If two or more consecutive parts of someone’s name are made into initials, we usually put a space after each period of the initial. However, while some style guides recommend this practice, others do not, so it’s essentially a matter of personal preference. Be consistent whichever method you use.
- J. R. R. Tolkien wrote The Hobbit and Lord of the Rings.
- The H. M. S. Bounty would never return home.
5. Formal titles like Mr., Mrs., Dr., and Fr. are types of word abbreviations that we most often use in their contracted-word forms. We almost always use a period at the end of these words.
- Dr. Johnson is performing surgery today.
- Mrs. Abernathy left her gloves on the counter.
- The wedding ceremony was officiated by Fr. McDonald.
Note: It has become commonplace to omit periods with certain abbreviated formal titles. For example, it is acceptable to use the abbreviation M.D. (medical doctor) without periods, as in “David H. Markot, MD, is my family doctor.” As well, the U.S. Postal Service no longer uses periods in the two-letter abbreviated names of states for addresses, as in NY (New York), KY (Kentucky), WA (Washington), etc.
6. Acronyms, like initials, are abbreviations of multiple words that are formed by using the first letter of each word. The difference is that acronyms are read out loud as a single word, and not as a series of letters. We don’t usually use periods after each letter of an acronym, but sometimes we do. If you’re not sure whether to use a period in an acronym, consult your textbook, dictionary, or the style manual of your organization.
- The surgeon used a LASER to cauterize the blood vessel.
- I plan on going to NASA this summer to watch the space shuttle launch.
- We need to get back home A.S.A.P.
- U.N.I.C.E.F. is a charitable organization that helps impoverished children.
7. Initialisms are the fourth type of abbreviation. They’re formed in the same way as acronyms, but they’re spoken out loud as individual letters rather than as a single word. Because they look like acronyms, they’re often mistakenly referred to as acronyms. The use of a period after each letter in an initialism is a matter of personal preference.
- Last night, I saw a U.F.O., so I called the F.B.I.
- Upgrading the CPU in my Windows PC should make it run faster.
Using a period with parentheses
If the material enclosed in parentheses comes at the end of a sentence, and can stand on its own as a complete sentence (independent clause), place a period inside the closing parenthesis. If the text inside the parentheses cannot stand alone as a complete sentence (dependent clause), place the period outside the closing parenthesis.
- Many of the terms in this book are technical in nature. (Please see the Glossary of Terms.)
- Many of the terms in this book are technical in nature (see terms in Glossary).
Using a period with quotation marks
If a sentence contains a quotation, and the quotation marks appear at the end of the sentence, the period should be placed inside the quotation marks.
- American astronaut Neil Armstrong was famously quoted as saying, “That’s one small step for man, one giant leap for mankind.“
- The president said today was, “. . . a great day for our country.”
- My nephew said that when he grew up he wanted to be a “. . . rock star, an athlete, and a theoretical physicist.”
One space versus two spaces after a period
In the past, it was standard practice to type two spaces between a period and the first word of the following sentence. This had to do with the limitations of typewriters and monospaced fonts.
With today’s word processing software, it is no longer necessary to use two spaces. The only exception would be if you are using word processing software and choose a monospaced font. In that case, you would probably want to use two spaces for better legibility; otherwise, use one space.
Periods used as decimal points
While many countries use a comma between the whole number and fraction of a decimal number, the United States and some other countries use a period.
- Are you aware that 3.1415 is the value of pi to four decimal places?
- I bought a pair of tennis shoes for $50.00.
- Dr. Abernathy prescribed 7.5 mg penicillin for the infection.