The other day I was in a restaurant whose menu touted "Our Specialty's." Today I was in one that crowed "Calamari at it's best." These aren't unique, and there's certainly no shortage of these misplaced apostrophes, but they've prompted me to whine about the problem today.
Humour columnist Dave Barry, in his guise of Mr Language Person, had this to say, some years ago:
Dear Mister Language Person: What is the purpose of the apostophe?
Answer: The apostrophe is used mainly in hand-lettered small business signs to alert the reader that an "S" is coming up at the end of a word, as in: WE DO NOT EXCEPT PERSONAL CHECK'S, or: NOT RESPONSIBLE FOR ANY ITEM'S. Another important grammar concept to bear in mind is that you should put quotation marks around random words for decoration, as "TRY" OUR HOT DOG'S, or even TRY "OUR" HOT DOG'S.
It's (yes) not rocket science; let's all get this right, every time:
- There's an apostrophe stuck in a contraction to represent the missing letters, as in the first word of this sentence ("there is" -> there's). Don't ("do not") forget it.
- Apostrophes (not "apostrophe's") are never used to make words plural.
- While it's ("it is") customary to use an apostrophe to make a plural of a short abbreviation that's ("that is") rendered in all caps (such as "PC's"), not all of us agree on this (what, after all, is wrong with "PCs"?), and it's only for short things ("Mind your P's and Q's", "three CD's"), and "short" fades quickly. "DVD's" and "ROM's" are already starting to go beyond the pale, and give up on anything longer than that. And never use an apostrophe when the abbreviation has become a word in its (not "it's") own right ("lasers", "radars").
- Possessives are a little trickier, since there's some inconsistency. Usually, we make a noun (but not a pronoun) possessive by adding an apostrophe and an "s": "Barry's blog", "the cat's paw" (as opposed to "the cats", which is plural), "the process's steps" (no exception for singular nouns that end in "s"!), "the children's game", "Bill Smith's car". To make a possessive of a plural noun that ends in "s", just stick a lone apostrophe at the end: "the cats' paws", "the processes' steps", "the adults' games", "the Smiths' car".
- For pronouns, we have special versions that are possessive, and we do not use apostrophes: "me" -> "my", "him" -> "his", "it" -> "its" (not "it's", the most common error here), "us" -> "our", and so on.
- Names that end in "s" are not plural, and still follow the "apostrophe + s" rule: "Chris's guitar", "Bridget Jones's Diary". Of course, this makes it complicated when we make "Jones" plural ("the Joneses") and then turn that into a possessive ("the Joneses' car").
- Out of custom, "Jesus" and "Moses" are excepted from the above rule, so their possessives are Jesus' and Moses'. Go figure.
The Chicago Manual of Style is a good reference for this and lots of other stuff. If you write much, get a copy.