Infinitive phrase
An infinitive phrase is the plain form of a verb introduced by 'to', plus any objects or modifiers that go with it ('to reach the summit before dark'), used as a noun, as an adjective, or most often as a statement of purpose.
He left at four to reach the summit before dark. The phrase runs from to through dark and answers why, which is the job infinitive phrases do best. The alternative is a whole clause, so that he could reach the summit before dark, and the infinitive gets there in three fewer words.
Infinitive phrase examples
It changes role depending on where it sits.
- Subject (noun): To be doubted was new to her.
- Object (noun): She wanted to leave before the speeches.
- Adjective: She had no reason to stay the night. The phrase describes reason.
- Purpose (adverb): She stayed to hear the verdict. The phrase says why.
- At the front: To reach the summit before dark, they left at four.
When it opens a sentence, it works like any initial modifier and needs the right subject next. To reach the summit before dark, the alarm was set for four never says who is climbing. That is a dangling modifier. Fix: To reach the summit before dark, we set the alarm for four.
Infinitive vs prepositional phrase
To is also a preposition. She went to the station is a prepositional phrase, because a noun follows. She went to meet the train is an infinitive phrase, because a verb follows.
Two things worth knowing
Split infinitives are fine. Splitting the infinitive means putting a word between to and the verb, as in to quietly leave. It is not a grammatical error in English, and rearranging a sentence just to avoid one usually makes it worse.
A run of infinitives tangles fast. She agreed to try to get him to promise to call. Each one is fine; four is a knot. Cut one or two: She agreed to get him to call.
When an infinitive phrase works as a noun, it behaves like a gerund phrase: a verb doing a noun's work, able to carry an object of its own and still slot into the sentence as a single piece. To be doubted was new and Being doubted was new say nearly the same thing.
Frequently asked questions
What is an infinitive phrase?
It is 'to' plus the base form of a verb, together with anything that goes with the verb, as in 'to reach the summit before dark'. It can work as a noun, an adjective or an adverb, and most often it explains why something happens.
How is an infinitive phrase different from a prepositional phrase with 'to'?
Look at the word after 'to'. If it is a verb, as in 'to leave early', it is an infinitive. If it is a noun or pronoun, as in 'to the station', it is a prepositional phrase.
Is it wrong to split an infinitive?
No. Putting a word between 'to' and the verb, as in 'to quietly leave', is not a grammatical error. Split it when that reads best and keep it together when that reads best.