7a Tod gave Brent his hat.
Another distinguishing feature of some pronouns, including his, is that they are gender specific. This feature could, under other circumstances, have made sentences similar to the one just cited perfectly clear. Thus:
7b Tod gave Tiffany her hat.
7c Tod gave Tiffany his hat.
But often we do not want to be or cannot honestly be specific about the sex of the person referred to by the pronoun.
8a The child cut his finger.
8b The child cut her finger.
8c The child cut his or her finger.
8d The child cut their finger.
His in the first example can no longer be defended as the all-purpose sexless pronoun that it never was. His or her will sometimes feel too cumbersome or self-conscious. Thus it seems rather likely that the last solution above is going to prevail as English continues to evolve, though for the moment many regard it as ungrammatical since their is a plural form and child is singular. Gender specificity is a pronoun problem. Avoiding inaccurate gender specificity has become one of the major challenges of good writing.
Yet another unusual feature of the pronoun class is that it continues to mark case, which was a decisive grammatical feature of English before it evolved into the word-order language it is today. His, her, and their are all possessives; so are whose, its, and so on. Each of these pronouns has what might be called a subject case and an object case as well as this possessive case. Compare them with the nouns in the following table:
case pronoun forms nouns subject: he she they who it Mary's John's possessive: his her(s) their(s) whose its Mary's John's object: him her them whom it Mary John
There are a good many pitfalls in the list above: using it's or who's for its and whose, writing they're or there when you mean their, and forgetting to distinguish between Marys and Mary's. None of these is an interesting mistake since all depend simply on the identity of pronunciation of these different forms. Much more interesting is the continuing capacity of English speakers to distinguish pronoun cases in some circumstances and their inability to do so in others.
9Who did you give the ball to?
10 Whom do men say that I am?
Both of these sentences could be described as ungrammatical because they contain pronouns in the wrong case. The first is the equivalent of saying
11 I gave the ball to he,
and the second to saying
12 Whom am I?
Though no native speaker would produce these last two sentences, most of us regularly produce statements similar to the first two examples, even if we are being careful--in the case of "Whom do men say that I am," especially if we are being careful. In this respect, then, there seems to be a real distinction between grammar--meaning 1 (what native speakers feel is right) and grammar--meaning 2 (the rules that can be extracted from our normal usage).
The domain of the first kind of grammar is speech; writing and reading allow or require you to be more analytical in your language use. You have to get your words to agree with each other if you want your reader to agree with you.