Adjectives function to describe specific qualities. This includes those detectable by the five senses, such as "quiet" and "round," opinions such as "good" and "pretty," personality traits such as "friendly" and "rude," qualities of time such as "annually" and states of being such as "dangerous" and "flammable."
Some adjectives serve to differentiate one noun or pronoun from another. In "that door," "that" is used as an adjective to identify which door. Likewise, in the sentence "you will need the largest ladder," the superlative adjective "largest" refers to the ladder of greatest size among others. Comparative and superlative adjectives, such as "better" and "best" respectively, must always be used in comparison to something else. In addition, adjectives may indicate the number of things being referred to, as in "five fish," "many pieces of paper" and "no cake left."
There are many cases in which a noun, pronoun or verb may be used as an adjective. In "car tire," the noun "car" is used as an adjective to clarify "tire." A pronoun can become an adjective as in "that computer." Verbs can be used as adjectives either in their "-ing" present participle forms as in "running start," or in the past participle as in "shattered vase."
Adjectives appearing directly before the word they modify are called noun phrase modifiers. When further emphasis is needed on the adjective, the predicate case can be used; this means the adjective is connected to the word it modifies by a linking verb such as "to become" or a copula like "to be." Examples include, "the car is stylish" and "my room has become cluttered."
Adjectives modify direct objects, following the direct object that they modify. For example in "they painted the room green," the adjective "green" is modifying "room" and providing more detail to the action of the transitive verb "to paint."