Separated by a Common Language: Abbreviations, Contractions, Acronyms, Initialisms, Clippings
The British English (BrE) and the American English (AmE) mainly differ in the ways they format abbreviations and quotations. Moreover, BrE does not share fondness for the Oxford comma despite its distinctively British name.
Strictly speaking, there are five types of abbreviations: abbreviations, contractions, acronyms, initialisms, and clippings.
British English and American English: The Use of Abbreviations
They are formed by omitting the end of a word:
Professor ⇒ Prof. paragraph ⇒ para.
In both BrE and AmE a period (full stop) should be placed to indicate the abbreviation:
Contractions are formed by omitting the middle of a word. There are two types of contractions:
Contractions formed without apostrophes:
Mister ⇒ Mr Doctor ⇒ Dr
BrE and AmE mainly diverge in the formatting styles of contractions/abbreviations. While the British English logically, and correctly, formats these “abbreviations” as contractions, the American English conveniently (and visually more appealingly) treats them as abbreviations.
Americans tend to place periods after contractions to make sure they are not mistaken for regular words. They basically treat them as abbreviations. Brits, however, want to be consistent: If a contraction ends with the same letter as the original word, no a period (full stop) should be used:
There are, however, some exceptions:
Contractions formed with apostrophes in both British and American English:
cannot ⇒ can't is not ⇒ isn't do not ⇒ don't I have ⇒ I’ve we are ⇒ we’re
Acronyms are formed from the initial letters of words and pronounced as words themselves, so no periods should intervene between the letters:
NATO NAFTA PIN AIDS
UNESCO UNICEF AWOL GOP
Initialisms are formed from the initial letters of words but are not pronounced as words.
In AmE, two-letter initialisms often take periods:
However, three-letter initialisms are generally written without periods:
In AmE, some 2-, 3-, and 4-letter initialisms may be written with periods (mostly in news and sometimes academic papers):
The AA initialism never takes periods:
BrE and AmE also differ in their punctuation of the shortened forms of academic degrees:
Lowercase Latin (and Other) Initialisms:
A number of commonly used lowercase initialisms of Latin terms usually take periods in both BrE and AmE:
With these ones, some variations may take place:
There are some exceptions, of course:
Initialisms of measurements never take periods:
In addition to Latin, some measurements still used in AmE are from Ancient Roman:
BUT: Place a period after in. (inches) so that to prevent confusion with the preposition in (in the school).
Clippings are acronyms that have become lexicalized as common words. They are formed by retaining at least one syllable of the original word. To maintain the readability of the acronyms-clippings, no periods are used in either BrE or AmE: