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, complementary to each other when taken in their two forms.
[§ 450]. In the absolute construction of a genitive case, the term is formed by the single word, only so far as the expression is concerned. A substantive is always understood from what has preceded.—This discovery is Newton's = this discovery is Newton's discovery.
The same with adjectives.—This weather is fine = this weather is fine weather.
And the same with absolute pronouns.—This hat is mine = this hat is my hat; and this is a hat of mine = this is a hat of my hats.
[§ 451]. In respect to all matters of syntax considered exclusively, it is so thoroughly a matter of indifference whether a word be an adjective or a genitive case that Wallis considers the forms in -'s, like father's, not as genitive cases but as adjectives. Looking to the logic of the question alone he is right, and looking to the
practical syntax of the question he is right also. He is only wrong on the etymological side of the question.
"Nomina substantiva apud nos nullum vel generum vel casuum discrimen sortiuntur."—p. 76.
"Duo sunt adjectivorum genera, a substantivis immediate descendentia, quæ semper substantivis suis præponuntur. Primum quidem adjectivum possessivum libet appellare. Fit autem a quovis substantivo, sive singulari sive plurali, addito -s.—Ut man's nature, the nature of man, natura humana vel hominis; men's nature, natura humana vel hominum; Virgil's poems, the poems of Virgil, poemata Virgilii vel Virgiliana."—p. 89.