I'm not English hence I don't know how this is called in the first place (that's why the title of this question should be changed) but what I'm referring to is this "s" used in English language to denote something belonging to someone/something or being related to something/someone:
I took my father's coat.
1st question
I wonder what that 's stands for? Does it abbreviate some longer word as it does when it abbreviates is or was (ie. He's tall)?
2nd question
Why do we only use apostrophe when doing the same thing in plural:
I made clients' incomes grow.
I know my examples may be bad/invalid but I would like to know some theory behind this as well as any exceptions to the rule if they existed… I know it's different when you refer to something of the first person. We don't say I's coat but rather My coat. This probably is an exception.
Best Answer
This is called the possessive case or the genitive case of a noun. (Possessive is the more common term, but it implies ownership; genitive is more general and implies a relationship.)
In Old English, there were many ways to put a noun into the genitive case, depending on count and gender. But after the 1500s, a noun could only be put into the genitive case with an -es ending. Eventually the e was dropped, leaving us with 's.
Sometime after, the plural genitive was reintroduced with the following convention: Form a plural genitive by adding just an apostrophe only if the normal plural noun ends in s; in all other cases, add -'s as normal. So beavers' and carpenters', but children's and people's. Sometimes you'll also see the convention applied to singular nouns ending with s (e.g., Jesus' ), but this is often discouraged.
Why my instead of I's? My is a possessive adjective and doesn't follow the normal rules.