Thanks to Riggin Waugh for sending me this link: www.apostrophe.org.uk
John Richards, a longtime working reporter and editor, founded The Apostrophe Protection Society
with the specific aim of preserving the correct use of this currently much abused punctuation mark in all forms of text written in the English language.
If you are as dismayed as Xtreme English by the recent rash of apostrophe faults committed by people, organizations, and publications she thinks should know better, you will welcome this simple, elegant explanation of where an apostrophe should go--and why.
The rules concerning the use of apostrophes in written English are very simple:
1. They are used to denote a missing letter or letters, for example:
I can't instead of I cannot I don't instead of I do not it's instead of it is
2. They are used to denote possession, for example:
the dog's bone the company's logo Jones's bakery (but Joneses' bakery if owned by more than one Jones)
... but please note that its, which is usually used as a possessive adjective (like our, his etc), does not take an apostrophe:
the dog ate its bone and we ate our dinner
Please click on the link and read the whole thing. Richards clarifies other common mishaps of English usage and has a message board and a raft of links to other grammar sites. He also adds this observation:
We are aware of the way the English language is evolving during use, and do not intend any direct criticism of those who have made the mistakes above. We are just reminding all writers of English text, whether on notices or in documents of any type, of the correct usage of the apostrophe should you wish to put right mistakes you may have inadvertently made.