Personal pronouns inflect to mark their case, making them unusual among English word classes. You may have noticed from the table of personal pronouns that there are two forms of the possessive case recorded. These are -- like so much in grammar -- dependent on the function of the word.
- The determinative possessive acts, as its name may suggest, as a determiner - that is as a word, usually in front of a noun, that helps the hearer or reader to determine which item is being spoken of. It may help you to realise the distinction to notice that the determinative possessive must, like an adjective, be used with a noun - virtually always before it. (This is why some grammarians call it the adjectival form.) Examples: "That is his car"; "May I borrow your book?", and "Have you seen our dog?"
- The independent possessive does not precede a noun. It acts independently, and behaves more like a pure pronoun. It stands by itself. Examples: "That's mine", "This one is his; that's hers over there" and "Ours is on the right; yours is on the left."
Notice that in the case of his, the independent and determinative forms are the same, but for all other personal pronouns, the independent possessive form has a consonant added to the determinative possessive form. This is an '-s' for all except 'my/mine' (and the archaic 'thy/thine'): our (determinative)/ours (independent) and their (determinative)/theirs (independent), for example. (There is no need for an independent possessive form for 'it' in academic English writing; its does exist, but is very rare even in colloquial English.)