Apostrophe’s … apostrophes’ … apostrophes?

I've lost count of the number of people who have asked me to write something about the apostrophe – largely because they get annoyed at the way other people use it incorrectly! :) So here goes – not all at once, though – treat this as part 1, to be continued.   

In English the apostrophe should not be used when the word concerned is just an ordinary plural. I wish I could say "not ever ... never ... never ever", but I can't, because there are a few exceptions. For now, though, please forget that any  exceptions exist, and simply avoid ever using an apostrophe with a normal plural noun, and in 99,999 percent of cases you'll be right. 

So ... the following are incorrect:

1. A competition for mother's and babie's.

2. We specialise in the grooming of pet's.

3. The Smith’s are a nice family.

4. CD’s and DVD’s at sale prices.

The correct versions of these examples would be:

1. A competition for mothers and babies.

2. We specialise in the grooming of pets.

3. The Smiths are a nice family.

4. CDs and DVDs at sale prices.

There are two major correct uses of the apostrophe in English:

a.       To indicate that one or more letters have been omitted from a word or phrase, as in: 

        1. We'll show you a better way. (Omission of "wi" from "will".) 

        2. It's the right thing to do. (Omission of the "i" of "is".)

b.      To indicate possession, as in:

1. A man's best friend is his dog.

2. A dog's best friend is his kennel.

If the possession involves a plural noun, the apostrophe comes after the plural "s", as in:

1. Dogs' best friends are their kennels.

2. These poems' greatest merit lies in their simplicity.

3. Ladies’ Golf Day.