This is the most complex punctuation mark and has two main functions- abbreviation or indicating missing letters and possession or indicating belonging.
For example, did not becomes didn’t, they will becomes they’ll, he would becomes he’d, and would have becomes would’ve. Also the same word can abbreviate different words, eg it’s abbreviates it is or it has, and what’s abbreviates is, has and does in for example what’s it called?, what’s he done? and what’s it mean?; further, ‘s can abbreviate has, or is, as in the food’s gone or she’s finished. The abbreviated word is joined to the word before to make one word.
Can not, will not and shall not have the special contractions of can’t, won’t and shan’t, where the first word has changed and missing letters; will not becomes won’t not willn’t, as this is easier to say, but am not doesn’t become am’t as this is hardly easier to say.
Some abbreviations, such as would’ve or nothing similar’s been done are less accepted in written form, and although in speaking more than one word in succession may be abbreviated, this isn’t done in writing- eg you can say they’ll’ve gone by now, or he’d’ve done it, but must write they’ll have or he’d have.
There are formations where words can’t be abbreviated, eg I have to go, She’s as good as I am or There it is don’t become I’ve to go, She’s as good as I’m or There it’s. and conversely there are formations where abbreviated words are used but their unabbreviated forms aren’t, eg Don’t you think so? or Won’t you go? don’t appear as Do not you think so? or Will not you go?.
Longer words can be abbreviated often for written purposes, eg government can become gov’t or boulevard blvd, or Johannesburg Jo’burg written or spoken; o’clock is short for of the clock, no longer used, and also the apostrophe is fixed in some names, eg O'Reilly.
Also apostrophes for missing letters or numbers at the ends or beginnings of words can be omitted if the meanings are still clear, eg phone, net, Feb 08, but retaining in non-standard English like ‘bout (for about) or ‘twas (for it was).
A dot after words can also denote abbreviation, eg Ltd. for limited, i.e. for that is to say (in Latin), Rev. for Reverend or Prof. for Professor but dots are increasing seen as unnecessary, particularly when the first and last letters are still in place, as in Mr, Dr or Sgt.
For example, Sue’s book, or the table’s legs. When the possessor’s name already ends in an s (or s sound ie z, x, se, ce, ze or xe), the ‘s is usually retained but can be omitted if it makes the word or phrase awkward to say, ie James’s or Julius’s but Williams’ or especially Moses’ or Socrates’ where there’s already an es type sound at the end of the word; however Chris's and Jesus's are used.
When the possessor is plural the s after the apostrophe is always omitted, eg the tables’ legs, boys’ game or bosses’ room.
The words its, theirs, ours, whose, yours and hers (also his and mine, from hes and mys) are already fixed as possessive and don’t have apostrophes: hence it’s and who’s are always abbreviations.The singular one's, somebody's, nobody else'sand also everyone's however take apostrophes, but never s’.
Men, women and children are also plural and to make them possessive, ‘s is added, eg women’s hats. s’ is never added, and chilrens, mens and womens also aren’t words. However though people is likewise already plural, s’ is used in refering to a number of peoples, eg the African peoples’ languages- and peoples is a word, as though a plural plural. Persons’ is also possible.
An s of course is also added to verbs without an apostrophe to denote third person possession, eg she thinks, he takes or it begins.
Names of companies may or may not use the apostrophe, eg Lloyds Bankdoesn’t but Sainsbury’s does- it may be removed when there’s no association with the company’s originators and the word becomes just a title; similarly the apostrophe is usually omitted in geographical names, eg Smiths canyon.
Possessors ending in a letter of an s sound that isn’t sounded can have an apostrophe without an s after it to indicate that the previous letter should be sounded, eg Descartes' ideas.
Ineg for convenience' sake or for goodness' sake the s after the apostrophe can be omitted because although these possessors aren’t plural they end with the s sound and are followed by a word beginning with s sound; proper nouns however, eg James’s sake, still retain it.
Where there is more than one possessor the apostrophe goes only after the last one mentioned, eg John and Sue’s party.
Apostrophes are needed in one hour's work, two weeks' holiday, and five dollars’ worth.
Abbreviating the i in is and leaving only the s at the end of the previous word can look superficially like possession, eg My name’s Sean.
Apostrophes are usually omitted when letters are removed from the start of a word, eg phone for telephone or netfor internet, other than when the shortening is less standard English, eg 'bout for about, or 'less for unless.
The apostrophe is not used to mark plurality, apart from cases like capital S’s or number 1’s, being clearer than Ss or 1s, even though this would normally denote possession by the S or 1; similarly dot your i's and cross your t's, grade A’s or yes’s, no’s, do’s and ex’s.Apostrophes can further be used to clarify the endings of unusual words, such as n'th rather than nth.
Passers-by,Attorneys General or rites of passage are examples of a possessor where the plural s is not placed on the end word, complicating placing of apostrophes.
Moreover the apostrophe is distinct from the same 9-shaped punctuation mark for closing a quotation, or marking feet and inches or minutes and seconds of degrees.
The apostrophe has numerous other minor uses.