The first class is the class of what may be called the oblique possessives; the name being founded upon the etymological fact of their being connected with the oblique cases of the pronominal inflection.—My, thy, his (as in his book), her, its (as in its book), our, your, their. These are conveniently considered as the equivalents to the Latin forms mei, tui, ejus, nostrum, vestrum, eorum.
The second class is the class of what may be called the absolute possessives; the name being founded upon the syntactic fact of their being able to form the term of a proposition by themselves; as whose is this? Mine (not my).—Mine, thine, his (as in the book is his), hers, ours, yours, theirs are conveniently considered as the equivalents to the Latin forms meus, mea, meum; tuus, tua, tuum; suus, sua, suum; noster, nostra, nostrum; vester, vestra, vestrum. How far either or both of these two classes of pronouns are cases, or adjectives, is a point of etymology that has already been noticed (Part IV., chap. 37).
How far either or both are cases or adjectives is, in syntax, a matter of indifference.
[§ 521]. There is, however, a palpable difference between the construction of my and mine. We cannot say this is mine hat, and we cannot say this hat is my. Nevertheless, this
difference is not explained by any change of construction from that of adjectives to that of cases. As far as the syntax is concerned the construction of my and mine is equally that of an adjective agreeing with a substantive, and of a genitive (or possessive) case governed by a substantive.
Now a common genitive case can be used in two ways; either as part of a term, or as a whole term (i. e., absolutely).—1. As part of a term—this is John's hat. 2. As a whole term—this hat is John's.
And a common adjective can be used in two ways; either as part of a term, or as a whole term (i. e., absolutely).—1. As part of a term—these are good hats. 2. As a whole term—these hats are good.
Now whether we consider my, and the words like it, as adjectives or cases, they possess only one of the properties just illustrated, i. e., they can only be used as part of a term—this is my hat; not this hat is my.
And whether we consider mine, and the words like it, as adjectives or cases, they possess only one of the properties just illustrated, i. e., they can only be used as whole terms, or absolutely—this hat is mine; not this is mine hat.
For a full and perfect construction whether of an adjective or a genitive case, the possessive pronouns present the phenomenon of being, singly, incomplete, but, nevertheless, complimentary to each other when taken in their two forms.