Words That Can Function as More Than One Part of Speech
Many words can function as more than one part of speech.
For example, nouns can function as adjectives:
The apartment building is tall.
In the sentence above, apartment is a noun that functions as an adjective. It modifies building.
Similarly, adjectives can function as nouns:
The natural world often pits the strong against the weak.
In the sentence above, the adjectives strong and weak function as nouns.
Verbals (infinitives, gerunds, and participles) often act like two different parts of speech.
An infinitive (the “to” form of a verb) can function as a noun, adjective, or adverb. Specialists often call these “nominal infinitives,” “adjectival infinitives,” and “adverbial infinitives”:
To err is human.
I have nothing to wear.
I’ll be delighted to attend.
In the examples above, to err functions as a noun, to wear functions as an adjective modifying nothing, and to attend functions as an adverb modifying delighted.
Present and past participles (the -ing and -ed forms of verbs) can function as adjectives:
Running into the room, she announced the news.
The winner, chosen at random, collected the prize.
In the sentences above, running and chosen function as adjectives. Running modifies she, and chosen modifies the winner.
Gerunds are the -ing forms of verbs that function as nouns:
Running in the park takes my mind off work.
In the sentence above, running functions as a noun.
Prepositions can also function as other parts of speech. For example, down often functions as a preposition, but it can function in other ways.
The puppies tumbled down the hill.
In the sentence above, the word down forms the prepositional phrase down the hill.
She turned down the thermostat.
In this sentence, the word down is an adverb modifying turned.
The down escalator is broken.
Here, the word down is an adjective modifying escalator.
The basketball players down three bottles of water each.
In this case, the word down is a verb.