A brief note on pronouns

A Facebook friend posted this Calvin and Hobbes cartoon, prompting some thoughts on English morphology, a topic coming up soon enough in my linguistics class:

One interesting thing about English is that some things people think are pronouns really aren't. In English, the personal reference sets are:

(1) I, we, you, she, he, they   [subject pronouns]
(2) me, us, you, her, him, them   [object pronouns]
(3) my, our, your, her, his, their   [possessive somethings]
(4) mine, ours, yours, hers, his, theirs   [possessive pronouns]

Note that I and me are true pronouns; they can occupy the Noun Phrase slot in a sentence:

I see Mary.  (subject position)
Mary sees me.  (object position)

The forms my and mine, on the other hand, are different. Mine is a true pronoun, but my needs the support of the Noun it specifies. Note the following responses to the question Which book does Mary see?.  By linguistic convention ungrammatical sentences are marked with an asterisk (*):

Mary sees my book.
Mary sees mine.
*Mary sees my.

Note that the English articles also follow this pattern:

Mary sees the book.
*Mary sees the.

These possessives, and the articles, fall into a class that linguists call Determiners.  Determiners in English precede their Nouns and occupy a syntactic node called Specifier, because they specify which or whose something the Noun references.  In English, specifiers include the possessives (my, our, etc.), the articles (the, a/an), and the demonstratives (this, that, etc.).

Traditionally, language arts teachers have referred to these forms as "adjectives," but they are not adjectives.  For one thing, they can't be made comparative or superlative (*myer, *myest).  For another, they can't be modified by very, as in *very my (book).