Most adjectives in English can describe nouns by functioning as noun phrase modifiers, subject complements, and object complements. Some English adjectives, however, can only appear in the predicates of sentences as subject or object complements.
Prototypical Adjectives
Adjectives are traditionally defined as words that describe nouns. For example, the adjectives gray, sleepy, and red describe the nouns puppy, girl, and barn in the sentences the gray puppy barked, the girl is sleepy, and the farmer painted the barn red. For more information on adjectives, please read the article Adjectives – The Qualifiers that Add Emphasis to Your Words.
Prototypical adjectives perform four grammatical functions in English: adjective phrase head, noun phrase modifier, subject complement, and object complement. For example, the adjective large functions as the head of the adjective phrase quite very large. The adjective angry likewise functions as a noun phrase modifier in the angry man, tall as a subject complement in your son is tall, and guilty as an object complement in the jury found the defendant guilty.
Prototypical adjectives also express degrees of modification. Adjectives in English can express three degrees: positive, comparative, superlative. Positive forms of adjectives are identical to the dictionary form as in smart and intelligent. Comparative forms take the suffix -er or the adverb more to compare two "things" as in smarter and more intelligent. Superlative forms that the suffix -est or the adverb most to compare more than two "things" as in smartest and most intelligent.
Prototypical adjectives can also be used attributively, postpositively, and predicatively. Adjectives used attributively immediately precede the modified noun as in purple in purple crayon. Adjectives used postpositively directly follow the modified noun as in elect in president elect. Adjectives used predicatively appear in the predicate as in wimpy in the boss is wimpy and plaid in the child colored the house plaid. The function of noun phrase modifier can be either attributive or postpositive while both the functions of subject complement and object complement are predicative.
Predicative Only Adjectives
Although prototypical adjectives can look like or do all or most of the adjectival characteristics listed above, some adjectives are limited in grammatical form and grammatical function. For example, a small number of English adjectives can function only predicatively. Some of the more common predicative only adjectives in English are:
- ablaze
- abreast
- afire
- afloat
- afraid
- aghast
- aglow
- alert
- alike
- alive
- alone
- aloof
- ashamed
- asleep
- awake
- aware
- fond
- unaware
Note that many of the predicative only adjectives begin with the letter a, which resembles other adjectival prefixes.
Examples of Predicative Only Adjectives
Unlike most adjectives in English, predicative only adjectives can only appear in the predicate of sentences. For example:
- My boss is abreast of the problem. (correct)
- I am keeping my boss abreast of the problem. (correct)
- *My abreast of the problem boss found a solution. (incorrect)
- *My boss abreast of the problem found a solution. (incorrect)
In the first sentence, the adjective abreast (and subsequently the adjective phrase abreast of the problem) functions as a subject complement, which is a word or phrase that follows a copular verb and describes the subject, in this case my boss. In the second sentence, the same adjective functions as an object complement, which is a word or phrase that follows and describes the direct object, also my boss. In both examples, the adjective appears in the predicate and therefore functions predicatively.
In the third and fourth sentences, however, the adjective abreast incorrectly appears attributively and postpositively. Unlike prototypical adjectives, predicative only adjectives like abreast and the others listed above cannot appear attributively (before a noun) or postpositively (after a noun). Therefore, the adjective abreast can only describe the noun phrase my boss as a subject complement or an object complement, never as a noun phrase modifier.
Exceptions
Although predicative only adjectives can typically function only as subject complements and object complements, some such adjectives can function as noun phrase modifiers when the adjective is modified by an adverb or another adjective. For example:
- The half-asleep child started crying.
- The wide-awake baby is watching the mobile.
- The very ashamed student admitted cheating on the test.
In the first two sentences, the adjectives half and wide modify the adjectives asleep and awake allowing both predicative only adjectives to be used attributively. In the third sentence, the adverb very modifies the adjective ashamed, also allowing for the attribute use of this predicative only adjective.