Period (.)

The period is a fundamental punctuation mark in English grammar. It primarily serves to indicate the end of sentences but has other uses as well.

Periods Used in Sentences

A period is used to end the following types of sentences:

Declarative Sentences

Declarative sentences make a statement or express an opinion. They convey information or ideas and are the most common type of sentence.

  • I lost my keys.
  • The sky is blue.

Imperative Sentences

Imperative sentences give commands, directions, or requests. They often imply the subject “you” but don’t always state it explicitly.

  • Close the door quietly.
  • Feed the cat before you leave.

Indirect Questions

Indirect questions convey the essence of a question in a subtle or indirect way, ending with a period rather than a question mark.

  •  I wonder what time it is.
  •  She asked if you were coming to the party.

Periods Used with Quotation Marks

In American English, the period always goes inside quotation marks:

  • She said, “This is my favorite book.”
  • The sign read, “No trespassing.”

Omit Period if Quotation is a Question

If the quotation ends with a question mark, a period is not used.

  • He asked, “Are we leaving now?”

Omit Period if Quotation is Exclamatory

If the quotation ends with an exclamation point, a period is not used.

  • She yelled, “Watch out!”

Periods Used with Parentheses

The placement of a period with parentheses depends on whether the parenthetical information is part of the main sentence or a complete, standalone sentence.

Part of the Sentence:

When parentheses add extra, non-essential information within a sentence, the period goes outside the closing parenthesis.

  • She carried a bag (a large, red one) to the market.
  • He arrived late (as usual).

Standalone Sentence:

If the parentheses enclose a complete, independent sentence, the period goes inside the closing parenthesis.

  • The meeting was postponed. (The room was double-booked.)
  • I forgot my book. (I always seem to forget it.)

Periods Used in Abbreviations

Periods are used in standard abbreviations:

  • Dr. (Doctor)
  • Mr. (Mister)
  • Feb. (February)

If a sentence ends in an abbreviation, the last period of the abbreviation terminates the sentence:

  • I need to meet with the CEO at 3:00 p.m.
  • She said she worked at Smith & Co.

British vs. American Abbreviations

In British English, certain abbreviations (Mr, Dr) are written without a period, but in American English, they always require one.

Periods Used in Acronyms

An acronym is a type of abbreviation formed from the initial letters of a phrase or group of words.

Acronyms are pronounced as complete words, rather than as individual letters. As a result, they are typically written without periods (though not always).

  • Scientists from NASA have confirmed the spacecraft’s location.
    (NASA = National Aeronautics and Space Administration)
  • The officer went AWOL following the attack.
    (AWOL = Absent Without Leave)
  • I need those documents finished A.S.A.P.
    (ASAP = As Soon As Possible; also written as ASAP, asap, or a.s.a.p.)

Periods Used in Initialisms

Initialisms are also formed from the first letters of words, but they are pronounced letter by letter instead of as a single word. Because they look similar, people often refer to initialisms as acronyms.

Unlike acronyms, initialisms may or may not include periods between letters, depending on the style guide or personal preference.

In American English, periods are more common in certain initialisms, but consistency is key.

  • I grew up in the US, but I’ve lived in London since my early 20s.
    (US = United States)
  • It took a long time, but I’ve finally earned my Ph.D.
    (Ph.D. = Philosophiae Doctor, Latin for “Doctor of Philosophy”)
  • I need to go to an ATM to get some cash.
    (ATM = Automated Teller Machine)
  • I thought I saw a U.F.O. fly over the field last night.
    (U.F.O. = Unidentified Flying Object)

Periods Used in Initials of Names

Periods are used with initials in names:

  • J. D. Salinger is an acclaimed author.
  • My cardiologist is Dr. L. S. Wells.

When to Use Periods in Lists

Lists with Complete Sentences

If the list items are complete sentences, use a period at the end of the sentences.

Please remember to do the following:

  1. Check your email.
  2. Submit the report.
  3. Attend the meeting.

Lists with Phrases

If the list items are phrases, periods are not necessary.

  • Morning yoga session
  • Grocery shopping
  • Important client meeting
  • Evening walk with the dog

Lists with single words

If the list items are single words, periods are not necessary.

  • widget
  • gismo
  • sprocket
  • doohickey

Spacing After a Period

Traditionally, two spaces followed a period due to typewriter limitations, as early typewriters used mono-spaced fonts that made extra spacing between sentences visually necessary.

Modern technology now allows for proportional fonts, which create a cleaner and more balanced look with just one space after a period.

Consequently, style guides such as APA, MLA, and Chicago now recommend using only one space to improve readability and adhere to contemporary design standards.

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