Definition and Examples of Periods: Full Stop

A period ( . ) is a punctuation mark indicating a full stopplaced at the end of declarative sentences as well as after many abbreviations. The period is actually called a full stop in British Englishaccording to R.D. Burchfield in "The New Fowler's Modern English Usage," and is also known as a full point. Rene J. Capponauthor of "The Associated Press Guide to Punctuation," explains that the period may appear small but it has an important function in punctuation:

"The period is a mere dot in the panorama of punctuationbut it packs an impressive punch. Unlikesaythe colon or semicolonit can bring a sentence to a complete halt."

As Merriam-Webster succinctly defines it: "A period is a point used to mark the end of a declarative sentence or an abbreviation."

History of Usage

The period originated with Greek punctuation in the third century B.C.according to Maria Teresa Cox and Riya Pundir in their article "The Mysterious Disappearance of the Punctuation Dot: An Exploratory Study," published in Fortell: A Journal of Teaching English Literature. The Greeks actually used three different dots at the end of sentences and phrasessay Cox and Pundir:

"A low dot '.' indicated a short breath after a short phrasea mid-dot '・' meant a longer breath after a longer passageand a high dot '˙' marked a full stop at the end of a completed thought."

Eventuallywith the popularization of block books—books printed from woodcuts in Europe around 1300—engravers disregarded the high and middle dots and retained only the low dotsignifying the end of a sentence. Laterwith Johannes Gutenberg's invention of the printing press and movable type in the mid-1400sprinters continued the tradition of using only the low dot as a period. William Caxtona British merchantwriterand printerbrought the printing press to England in 1476—along with the low dotor period.

Cox and Pundir note that some writers and grammarians worry that the period is falling out of favor in the age of texting and electronic mailin favor of exclamation points, ellipsesline breaksand emoticons. They note that a 2015 survey conducted by the Department of Psychology at the State University of New York at Binghamton found that only 29 percent of American students were using a full stopor periodbecause they consider it to be a "bad way to convey heartfelt emotions."

Purpose

As discussedthe period is used to convey the end of a sentence or abbreviation. But it has other uses. Cappon in "The Associated Press Guide to Punctuation," as well as June Casagrande in her book "The Best Punctuation BookPeriod.," describe the period's purpose.

Finality: The period can mark the end of a sentence or sentence fragmentas in "Osama bin Laden has given a good imitation of the devil. To the Westat least." Or in: "Joe works here." "Eat." "Leave now." Casagrande uses the period (.) to mark the end of her book's titleright after the word "period," which is a sentence fragment. She likely does so to add emphasis and convince readers that hers is the final word in punctuation.

Initials and abbreviations: Periods are generally used when there are two letters in the initialsuch as U.S.according to "The Associated Press Stylebook." Howevers differ with some guidessuch as The Chicago Manual of Style Onlinesaying you should omit the periods. Even the AP spells the abbreviation for the United States as US in headlines.

State names: These take a period per AP and other s when you are not using postal ZIP code abbreviations. So you would have: Ala., Md.and  N.H.where by comparisonthe ZIP code abbreviations would omit the periods: ALMDand NH.

Abbreviations that end in lowercase letters: Some examples are  Gov.Jr.e.g.i.e.Inc.Mr.and et al.

Mathematics–place value: In mathematicsthe period is called a decimal point. For examplein the number 101.25the number placed to the right of the decimal point—in this case, 25—indicates 25/100 or twenty-five one-hundredths. The period/decimal point is often used with numbers. So$101.25 would read "101 dollars and 25 cents."

Ellipses: Ellipses—also called ellipses points—are three equally spaced points commonly used in writing or printing to indicate the omission of words in a quotation. They are also known as ellipsis dots or suspension points.

Correct and Incorrect Use

Since printers dropped the use of the high and mid-dot centuries agothe period has actually been the easiest punctuation mark to understand. But it is far from the easiest to use. Punctuation experts note that writers have long struggled with the rules for correctly placing the period. Casagrande gives these tips on the rules and correct use of the period.

Quotation marks: A period always comes before a closing quotation mark. Right: He said"Get out." Wrong: He said"Get out". Note that this rule applies to American English. British English requires that you place the period after the quotation mark.

Single quotation marks: A period always comes before the closing single quotation mark: He said"Don't call me a 'jerk.' "

Apostrophe: An apostrophe indicates the omission of one or more letters from a word. You do place the period after the apostrophe at the end of a sentence but before the final quote mark: He said"I know you were just talkin'."

Ellipses (...): The AP says you should treat ellipses as a three-letter wordconstructed with three periods and bounded by two spacesas shown here. If the ellipses come after a complete sentencehoweverplace a period before the ellipsessuch as in Martin Luther King Jr.'s famous words: "I have a dream....I have a dream today." 

Dashes: The dash (—) is a mark of punctuation used to set off a word or phrase after an independent clause or to set off a parenthetical remarksuch as wordsphrasesor clauses that interrupt a sentence. Never use a period before or after a dash. A correct example of how to use a dash effectively (and omit any periods) would be Colonel David Hunt's quote from his article "On the Hunt" published in the National Review on June 252003: "We can't be politically correct—right or left—in the war on terrorism. Period." Note that the only periods are placed after the end of the first sentence and at the end of the fragment, Period.

Initialism: An initialism is an abbreviation that consists of the first letter or letters of words in a phrasesuch as EU (for European Union) and NFL (for National Football League). Omit periods from initialisms. 

Falling Out of Favor?

As discussedperiods are often omitted in text messages. Nonethelesssays Claire Fallonwriting for the Huffington Post in a June 62016article"There hasn’t been much evidence that a laissez-faire attitude toward the period is migrating from digital messaging to the broader category of the written word."

HoweverRichard Lederer and John Shore in "Comma Sense: A Fundamental Guide to Punctuation" argue that writers are more frequently using other punctuation marks when they should be using the simple period:

"Every sentence that's not an exclamation or a question must end with a period. And because people are by and large too proud to ask too many questions and too shy to go around hollering all the timethe vast (not the half-vast) majority of sentences are what are called declarative statements—statements that just say something and therefore end in a period."

Sources

CapponRene J. "The Associated Press Guide To Punctuation." Basic BooksJanuary 2003.

LedererRichard. "Comma Sense: A Fun-damental Guide to Punctuation." First editionSt. Martin's GriffinJuly 102007.