As I have written repeatedly, the line between grammatical forms is blurry at best, especially among lexical categories like noun, verb, and adjective. Grammatical form and grammatical function distinguish one word class from other. The lines between functional categories are typically much clearer than the lines between lexical categories. As closed classes that do not readily accept new members, functional categories such as pronoun, preposition, determiner, and conjunction are much clearer. Unfortunately, some grammar book lump possessive determiners together with possessive pronouns. Or worse, erroneously label possessive determiners as possessive adjectives.
Determiners Versus Adjectives
The words my, your, his, her, its, our, and their are possessive determiners. Determiners provide non-attributive information such as definiteness, familiarity, location, quantity, and number about a nominal form, functioning as determinatives. Determiners are not adjectives. Repeat after me: Determiners are not adjectives. Adjectives are words that describe nouns. Adjectives can precede nouns. Determiners can also precede nouns. But syntactic position is not the only factor in determining the category of a word.
The internal structures, or grammatical form, that distinguish adjectives from other word classes are degrees of modification. Prototypical adjectives express three degrees of modification: positive, comparative, or superlative. The positive form is the base form of the adjective. The comparative form expresses a comparison between two entities in quality, quantity, or degree. The superlative form expresses the highest degree of comparison.
- I see a big tree. (positive)
- I see a bigger tree. (comparative)
- I see the biggest tree. (superlative)
- I see a beautiful tree. (positive)
- I see a more beautiful tree. (comparative)
- I see the most beautiful tree. (superlative)
English has two parallel systems of comparison. The morphological system uses the suffixes –er and –est, with some anomalous forms. The syntactic system uses the adverbs more and most. All adjectives in English have a positive form. Many, but not all, have comparative and superlative forms. Determiners, on the other hand, do not vary in internal structure.
While adjectives can express three degrees of modification , determiners do not exhibit morphological change. One can say the tree but not *the-er tree,*the-est tree, *more the tree, or *most the tree. The words my, your, his, her, its, our, and their do not have comparative or superlative forms because my, your, his, her, its, our, and their are possessive determiners, not possessive adjectives.
Determiners Versus Pronouns
Both determiners and pronouns belong to closed, functional categories. Neither determiners nor pronouns exhibit morphological change. Possessive can be defined as the expression of possession of or some other relationship to another form. The English possessive determiners are my, your, his, her, its, our, and their. Some English possessive pronouns are mine, yours, his, hers, its, ours, and theirs. Notice that the determiners his and its are identical to the pronoun his and its. The other determiners and pronouns are likewise similar: my~mine, your~yours, her~hers, our~ours, their~theirs.
Possessive determiners and possessive pronouns, however, differ significantly in grammatical function. Possessive determiners function only as determinatives. Determinatives are words that express additional information such as definiteness, proximity, quantity, and relationships about a nominal form. In That tree is my tree, the determiners that and my do not provide descriptive information about the noun tree like an adjective would. The possessive determiners my, your, his, her, its, our, and their perform only the grammatical function of determinative.
Nominal functions are grammatical functions prototypically performed by nouns, noun phrases, and noun clauses. As a nominal form, possessive pronouns can perform multiple nominal functions: subject, subject complement, direct object, indirect object, prepositional complement, and appositive.
- Hers arrived today. (subject)
- That child is mine. (subject complement)
- The storm broke theirs. (direct object)
- We gave ours a bath. (indirect object)
- I am looking forward to yours. (prepositional complement)
- That cat, his, dug up my garden. (appositive)
Possessive determiners do not perform nominal functions. Possessive pronouns do not function as determinatives.
Despite similarities in pronunciation and spelling, possessive determiners and possessive pronouns are two different grammatical forms that perform distinctly different grammatical functions. Neither word class exhibits morphological change. The possessive determiners my, your, his, her, its, our, and their function only as determinatives. The possessive pronouns mine, yours, his, hers, its, ours, and theirs can function as subjects, subject complements, direct objects, indirect objects, prepositional complements, and appositives. Possessive determiners are not adjectives. Possessive determiners are also not pronouns.
Brinton, Laurel J. & Donna M. Brinton. 2010. The linguistic structure of Modern English, 2nd edn. Amsterdam: John Benjamins Publishing Company.
Hopper, Paul J. 1999. A short course in grammar. New York: W. W. Norton & Company.
Huddleston, Rodney. 1984. Introduction to the grammar of English. Cambridge: Cambridge University Press.