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A full stop (British, New Zealand and Australian English) or period (American English and Canadian English)^[1] is the punctuation mark commonly placed at the end of sentences. In the 21st century, it is often also called a dot.^[2] In conversation, as opposed to linguistics, the term is often used to mean “the end of the matter.” (For example, “We are calling a full stop to discussions on this subject.”)

History

The period symbol derives from Aristophanes of Byzantium who invented the system of punctuationwhere the height of placement of a dot on the line determined its meaning. The high dot (^.) was called a “periodos” and indicated a finished thought or sentence, the middle dot (·) was called a “kolon” and indicated part of a complete thought, while the low dot (.) was called a “komma” and also indicated part of a complete thought.^[3]

Usage

Abbreviations

A period is used after some abbreviations.^[4] If the abbreviation ends a declaratory sentence there is no additional period immediately following the full stop that ends the abbreviation (e.g., My name is Gabriel Gama, Jr.) This is called haplography. Though two periods (one for the abbreviation, one for the sentence ending) might be expected, conventionally only one is written. In the case of an interrogative or exclamatory sentence ending with an abbreviation, a question or exclamation mark can still be added (e.g., Are you Gabriel Gama, Jr.?).

Titles

In British English, abbreviations of titles often omit a period, as in Mr, Dr, Prof, Rev, Gen, which in American English would be given as Mr., Dr., Prof., Rev., Gen.According to the Oxford A–Z of Grammar and Punctuation, “If the abbreviation includes both the first and last letter of the abbreviated word, as in ‘mister’ and ‘doctor’, a period is not used.” This does not include Professor, Reverend, General.^[5]

In this use, the period is also occasionally known as asuspension mark. This originates from the old practice of marking the end of an abbreviation with the final letter superscript and a dot beneath it (though still “suspended” above where a period would go). Another use of the suspension mark can be seen in examples such as the “c” in “Mc” (e.g., the Rand McNally logo).

Acronyms and initialisms

In acronyms and initialisms, periods are somewhat more often placed after each initial in American English (e.g., U.S. and U.S.S.R.) than in British English (e.g., US and USSR).^{[citation needed]}

Mathematical usage

The glyph has two alternative uses with regard to numbers. It can be used either as a decimal separatoror to present large numbers in a more readable form. The former use is more prevalent in English-speaking countries. In much of Europe, Southern Africa and Latin America (with the exception of Mexico due to the influence of the United States), a comma is used as a decimal separator, while a full stop or a space is used for the presentation of large numbers. The following are examples where the comma is or would be used as a decimal separator:

• 1.002,003 or 1 002,003 (One thousand and two and three thousandths)
• 1.002.003 or 1 002 003 (One million two thousand and three)

In countries that use the comma as a decimal separator, the full stop period usage is impractical in cases where the full stop is used as a decimal separator, hence the use of the interpunct: 5.2 · 2 = 10.4.^{[citation needed]} This notation is also seen when multiplying units in science; for example, 50 km/h could be written as 50 km·h⁻¹ (this can also be written as 50 km h⁻¹).