Apotheoses S
 

I could have sworn when I was in school there were two apothoses. One for "possession" and one for "is".

Example:

Johns' bag is red.

John's worried.

Am I wrong or has the rules changed?

You've got me at a loss here...
I thought I would agree with you, but the longer I think about it, the less I'm sure of that.

Now, English isn't my primary language, but isn't it called an apostrophe?
(took me a couple of reads to figure out what you meant, no offense )

It's all the same apostrophe, but it is used in a couple of ways.

One is to show possession: John's is a singular possessive, Johns' would be plural possession. The exception to this is the posessive of "it" which is "its".

The apostrophe is also used in contractions to show that letters have been taken out. "Do not" becomes becomes "Don't" and so on. You could use this for "John's angry," the meaning is clear from context.

Silvy, Sorry about the misspelling there. Should of used a dictionary.

Ratman,

So Johns' is plural and John's is singular. Damn, I always thought that the s' is for possession. It doesn't make sense if I understand it.

Example:

Where are Johns' bags.

Would the "s" at the end of "bag" mean that is plural and the "s' " at the end of John means they belong to him?

Example:

Where are Johns' bag at?

To me that mean their is only one bag, not two, so the plural " s' " at the end of John doesn't make sense.

So I'm still confuse, I could not be understanding it. I vaguely remember a fuss about the 's in McDonald's. Some teachers somewhere thought it was bad grammar and they should of kept it McDonalds'

I always thought " 's" always stood for "is". And "s' " is for possession.

I think that John should take possession of the bag and GET THEE HELL outta there!

I got excited, hee, I'm such a word geek. I thought we'd be talking about "apotheosis" which means deification or the quintessence of something. That's a favorite word that Flannery O'Connor used.
As far as the *apostrophe* you are correct about the different uses. If you were talking about a bunch of clients that a hooker had, and if their wallets were stolen, then you'd be wondering had the Johns' wallets been stolen. If you had a friend named John, and were wondering if his wallet had been stolen, then you'd ask if John's wallet had been stolen. One is for a group, the other is for an individual.
However, it's always best to check the Chicago Manual of Style. Plus, they'll give you classier examples :P

As Shyla Loral said, obliquely, "s'" shows a plurality of possessors, "'s" hows a singularity of possessors. Which you use is determined by the number of people possessing, not the number of things possessed.