Why are they both not 'it's?'
According to this rule of grammar:
it's: a contraction if it is (it's a rainy day)
its: possessive pro-noun, usually an object or an animal whose gender is unspecified.
But if that 'it' had a name, say Rover the dog, or Kermit the frog, then it wouldn't be. 'its ball' it would be 'Rover's ball.' Why not then use 'it's' as well?
Like some other rules in English this one makes no logical sense to me.
Because if it weren't like that, you wouldn't be asking this question.
<<Like some other rules in English this one makes no logical sense to me. >>
English isn't really a rules-language anyway. This is one of the reasons it's so easy compared to other languages with lot of rules (Sanskrit, for example).
It's better to take it easy when learning English and not worry about rules, inflections, etc. -- just go out and soak up the language using the stress-free "massive input" method.
I be happy hearing that English not have rules. It make it much more easily learning this language. That there are not grammar in the English is very good thing for I.
<<I be happy hearing that English not have rules. It make it much more easily learning this language. That there are not grammar in the English is very good thing for I. >>
English does have conventions instead of hard-and-fast rules. There are sentences that are more likely to be uttered by native speakers, and also sentences that less often heard from native speakers. As far as grammar goes, the goal in learning English is to say things in a more typical way, and not in an unusual non-native way.
There's no "Royal Academy of the English Language" (or more likely a "National English Language Regulatory Commision (NELRC)") to make rules. There's nothing that says what you wrote is "wrong". It's just that you don't often see native speakers write that way.
Although I can't defend any clear logic in the lack of an apostrophe in the weak possessive pronoun "its", you can remember whether there should be an apostrophe by comparison to the other weak possessive pronoun ending in "s" that also lacks an apostrophe: "his".
Tickle its tummy. Tickle his tummy.
That how I remember how to get it right, anyway.
For the same reason there's no apostrophe in hers or his or yours -- the S is part of the word already, not an addition used to show possession like it is in Charlie's or the cat's.
I agree with Uriel. If it were 'he's' instead of 'his', then maybe it would be understandable to ask this question - but just because it happens to end with an 's' doesn't mean to say that that 's' is the same kind of 's' that you add after an apostrophe.
Etymologically, they are the same morpheme. The "s" signified the genitive case in English.
Uriel and Caspian are both wrong; Guest is right. The s shows possession, just like the s in "his".
"Its" begins to appear much later than "his" or "her" - in the 16th century; before then, the neuter possessive was "his".
"Its" was commonly written "it's" until about the 1820s. You can find it in original-spelling editions of Jane Austen's novels, for instance, together with "your's".
Obviously English has rules, but there are a lot of peculiarities in English, that you just have to accept, rather than demanding a logical reason. Like "good, better, best" and "go, went" and "is, was, will be."
99% of English speakers have no idea WHY it is like that. It's just something you learn, and then it feels natural.
<there are a lot of peculiarities in English, that you just have to accept, rather than demanding a logical reason>
The peculiarities can be explained, not by logic, but by etymology and a knowledge of the history of English.