Full stop
Full stops (also known as periods) mark the end of a written sentence, which may be, grammatically, a Major (complete) or Minor (incomplete) Sentence, according to the type of text. They are also used to indicate abbreviations and decimal points. Awareness of them should be developed from the earliest encounters with text at Level A. Three full stops together (ellipsis, or ‘triple dot’) indicate that a number of words have been omitted.
1. Full stops, together with initial capital letters, mark sentence boundaries in all written texts. In formal continuous prose, they indicate only Major Sentences, apart from quoted materials, but in less formal texts, such as advertisements and much modern journalism, they can punctuate Minor Sentences. (This is what you need. To put you at your ease.) In formal continuous prose, however, grammatically separate clauses can be linked within a written sentence by means of semicolons or colons. (He is not saying that he does not want to do it; he is saying that he is not able to do it.) The tendency of some writers to link grammatically separate clauses by means of a comma (‘comma splice’) is still not acceptable usage in most formal or semi-formal writing.

2. Usage for abbreviations in Britain seems to be changing very quickly, as part of the current trend towards ‘lighter’ punctuation through the influence of word-processing. Some authorities still advocate the use of the full stop in words where first and last letter are included (Mrs., Dr., Rd.) but others point out that the full stop is now frequently omitted in such abbreviations. Some British writers also omit the full stop after initials for names (‘open punctuation’, as in J Smith), but it is still expected in American usage and is also fairly widely advocated in Britain. Parts of words or two-part abbreviations (Eng.; Cres.; a.m.; e.g.; M.A.) still tend to have full stops but acronyms such as NATO (North Atlantic Treaty Organisation), UCCA (University Central Council on Admissions) are rarely punctuated.

3. Full stops are used for the decimal point, in numbers and in currency: 9.25 (nine point two five) and 9.26 (nine pounds 26 pence).

4. Ellipsis is used to indicate places where words have been omitted, usually in a reference to an extract (Ellipsis … to an extract). It is also used to indicate pauses within direct speech ("I’m not sure … I’m afraid I will have to re-consider," she said) and where a sentence or piece of direct speech is left unfinished for stylistic effect (Was it true? He wondered … He didn’t know!).
Punctuation conventions in Modern Languages and American English. Major sentences, minor sentences in different registers and genres.
Meaning discrimination, Written style
See also
Capital, Punctuation, Sentence

French, German, Spanish