With apostrophes, possession is nine tenths of the issue.
To indicate possession, an apostrophe needs to be placed before a possessive s in the singular case (a dog’s life) and after a possessive s in the plural (the dogs’ tails). Simple.
Of course, if the plural form is one of those rare versions in English with no s, then you add it as you would a singular form: for example, the children’s toys or the women’s successes.
But what happens if the word already ends in an s? Here, the snaggle-toothed leopard of controversy rears its awkward head.
There are two schools of thought. One school teaches its pupils to place a lone apostrophe after the s of a proper noun or name to do all the work (e.g. Bridget Jones’ diary, Paris’ underground network) but add an extra s to other nouns (e.g. the class’s yearbook, the platypus’s beak).
The other school teaches that the apostrophe and s should be used together as often as possible: in particular, when the word tends to be pronounced with an extra s sound (e.g. Mr Jones’s smartphone, Paris’s museums).
Different authors will work to different style guides, so you have to find what works best for you.
The apostrophe replaces a letter or letters that have been removed, with the remaining letters sitting tightly on either side: for example, I will becomes I’ll and we cannot becomes we can’t.
This isn’t allowed, though, for every contraction that you might hear spoken every day.
For example, I have will be abbreviated to I’ve if it is being used as part of the present perfect tense (e.g. I’ve got a terrible headache) but not simply in the present tense (e.g. I have a terrible headache), even though they would both be pronounced in similar ways in spoken English.
I’ve a terrible headache would generally be incorrect when written down.
This is an area where the swirling tides of grammar fashion have left many people floundering.
It was once quite common for commas to be used for the plural versions of abbreviated nouns and numbers: for example, the MP’s or the 1990’s.
However, the tide has turned and it is now best to leave the apostrophes out (the CDs, the 1980s), unless it would be confusing to do so.
For example, the class of ’92 makes it clear that they graduated in 1992, whereas the class of 92 may mean that there were almost a hundred people in the class.