For most things, this is very clear. If it belongs to someone, possessive, then an apostrophe S is required at the end of the word or name.

Examples: That is the dogs dish. That belongs to Sallys aunt.

If it is a contraction, and two words are pushed together with some letters missing, then an apostrophe replaces the missing letters.

Examples:

Do not = Dont

Could not = Couldnt

But then there are the oddball exceptions to this rule, where no one really knows why things are done this way, we just have to learn that they are.

Examples: Will not = Wont (shrug)

Yet, most people get this right most of the time. The one that seems to cause the most problems is its versus its.

Because the apostrophe contraction for its means IT IS, the possessive form of this word does not include a contraction. Presumably, this was done in order to alleviate confusion between the two words, but in actuality, most people get it wrong, because it is an exception to the possessive rule above.

ITS is a contraction that stands for IT IS. Anytime you want to use IT IS, you can replace it with ITS.

ITS is the possessive form of the word IT, meaning that IT owns or possesses something.

Example: The building was destroyed in the fire, almost completely. Its not easy to understand why its door frames were still standing.

The first instance of ITS stands for IT IS, but the second instance of ITS refers to the door frames belonging to the building. IT is the building, and ITS is used to denote possession of the door frames. Silly example, I know, but it makes its point. Ah, theres another instance or ITS used in the possessive.

I will be writing more in the future about other confusing possessives, such as how to use the apostrophe when words end in S and SS, and more about possessives versus plurals, but for now, remember:

A contraction means a letter or several letters have been removed, and the apostrophe takes the place of the missing letters.

A possessive ends with an apostrophe S and indicates ownership or belonging to or possession of something.

Michelle L Devon
http://www.accentuateservices.com