An infinitive phrase is a group of words built around an infinitive, usually to + the base form of a verb. It may also include words that complete or modify the action.
For example:
Maya hopes to finish the painting before Friday.
The highlighted phrase tells us what Maya hopes to do. Infinitive phrases can also perform other functions in sentences, depending on how they connect to the surrounding words.
How Is an Infinitive Phrase Formed?
An infinitive may stand alone or appear with an object, complement, or modifier.
Consider:
The technician agreed to inspect the old wiring carefully.
The phrase contains three main parts:
- Infinitive: to inspect
- Object: the old wiring
- Modifier: carefully
Inspect names the action, the old wiring receives it, and carefully describes how the inspection will be carried out.
Not every infinitive needs an object.
The children wanted to leave early.
Here, early modifies to leave by telling us when the children wanted to leave.
Some infinitives take complements rather than objects:
Priya hopes to become an architect.
An architect is a subject complement within the infinitive construction. It tells us what Priya hopes to become.
Where Does an Infinitive Phrase End?
Finding the infinitive is often straightforward. Deciding which surrounding words belong with it can take more care.
Consider:
The technician promised to replace the cables before lunch.
The sentence allows two interpretations. The technician may have made the promise before lunch, or the replacement may have been scheduled for before lunch.
To make the timing of the promise clear, we could write:
Before lunch, the technician promised to replace the cables.
If the replacement deadline matters, we could write:
The technician promised to complete the cable replacement by noon.
These examples show why you should not automatically treat every word after an infinitive as part of its phrase. A modifier may relate to the infinitive action or to another part of the sentence.
Infinitive constructions are nonfinite. Their verb forms do not independently show tense or subject agreement in the way finite verbs do.
Functions of Infinitive Phrases in Sentences
Infinitive phrases can serve as subjects, complete the meanings of verbs or adjectives, modify nouns, and express purpose.
Their function depends on how they relate to the rest of the sentence.
Infinitive Phrase as a Subject
To restore the painting will take several months.
The infinitive phrase functions as the subject of will take. It identifies the activity that will require several months.
English also commonly uses an introductory it construction:
It will take several months to restore the painting.
Here, it occupies the grammatical subject position, while the infinitive construction specifies the activity being discussed.
Both sentences are grammatical, although the second often sounds more natural in everyday English.
Infinitive Phrase as a Verb Complement
The curator hopes to restore the painting.
The infinitive phrase completes the meaning of hopes. It tells us what the curator hopes to do.
Another example:
The committee agreed to restore the mural.
Here, the infinitive completes the meaning of agreed.
Different verbs take different complement patterns. Our Gerund vs. Infinitive guide explains those choices in detail.
Infinitive Phrase as a Subject Complement
Her goal is to restore the painting.
The infinitive phrase follows the linking verb is and explains what her goal involves.
It functions as a subject complement rather than the subject of the sentence.
Infinitive Phrases Modifying Nouns
An infinitive phrase can provide information about a noun.
The team found a damaged mural to restore.
The infinitive phrase modifies mural, identifying it as something available or intended for restoration.
Another example:
The assistant has several reports to review.
The reports are the things to be reviewed. The infinitive describes the task associated with them, but it does not independently tell us who will carry out that task.
Infinitive Phrases Expressing Purpose
The team stayed late to restore the mural.
The infinitive phrase explains why the team stayed late.
Compare these three sentences:
| Sentence | Function of the infinitive |
|---|---|
| The team agreed to restore the mural. | Completes the meaning of agreed |
| The team stayed late to restore the mural. | Expresses the purpose of staying late |
| The team found a mural to restore. | Modifies mural |
The infinitive constructions describe similar activities, but their grammatical roles differ.
A useful way to recognize a purpose infinitive is to ask Why did the main action happen?
Why did the team stay late?
To restore the mural.
That question works because the infinitive explains the reason for staying late. In agreed to restore the mural, the infinitive instead completes the meaning of the verb agreed.
Infinitive Phrases Completing Adjectives
Infinitives can also complete the meaning of adjectives.
The instructions were easy to follow.
The infinitive tells us what was easy. The instructions are understood as the things being followed.
Similarly:
The task was difficult to complete.
The infinitive identifies the activity described as difficult.
Infinitive Phrases and Commas
An introductory infinitive phrase expressing purpose is commonly followed by a comma:
To complete the repair, the technician needed special equipment.
Now compare:
To complete the repair would require several hours.
Here, the infinitive phrase is the subject of the sentence, so no comma separates it from the predicate.
The punctuation reflects how the construction functions, not merely where it appears.
Who Performs the Action in an Infinitive Phrase?
An infinitive often has an understood subject rather than one stated directly within the phrase.
Who performs its action depends on how the infinitive connects to the rest of the sentence.
When the Main Subject Performs the Action
Nina planned to lead the tour.
Nina is the person making the plan, and she is also understood to be the person who will lead the tour.
Another example:
Elena hopes to win the competition.
Elena is both the person hoping and the person expected to perform the action expressed by win.
When Another Person Performs the Action
Nina asked Omar to lead the tour.
Omar is expected to lead the tour. Nina is the person making the request.
Similarly:
Elena encouraged Marcus to enter the competition.
Marcus is the person expected to enter, while Elena is encouraging him.
The main verb helps establish who is understood to perform the infinitive action.
When the Infinitive Has an Explicit Subject
Some infinitive constructions include a subject introduced by for.
It is important for everyone to follow the instructions.
Within the highlighted construction, everyone is the subject of to follow the instructions.
Another example:
The manager arranged for the team to meet on Monday.
The team is expected to meet. The manager arranged the meeting but is not necessarily one of its participants.
When the Subject Depends on Context
Consider:
Priya gave the assistant a document to translate.
The assistant is a natural candidate for the person expected to translate the document, but the sentence does not make that arrangement completely explicit.
If the intended meaning matters, we can make it clearer.
Priya asked the assistant to translate the document.
Now the assistant is clearly expected to perform the translation.
Priya took the document home to translate it herself.
In this sentence, Priya is the intended translator.
The nearest noun is not always the understood subject of an infinitive. Sometimes the surrounding context is needed to establish who will perform the action.
To-Infinitives and Bare Infinitives
English uses infinitives both with and without to.
A to-infinitive includes to, while a bare infinitive uses the base form of a verb without it.
| Form | Example |
|---|---|
| To-infinitive | to open the window |
| Bare infinitive | open the window |
To-Infinitives
To-infinitives occur in several common patterns.
The visitors decided to stay another night.
She has an important letter to write.
We stopped at the shop to buy some water.
The first completes the meaning of a verb, the second modifies a noun, and the third expresses purpose.
Bare Infinitives
Bare infinitives commonly appear after modal verbs and certain other verbs.
After modal verbs:
The technician must check the equipment.
The modal must is followed by the bare infinitive check.
After let and make:
The coach let the players rest for a while.
The sudden noise made everyone turn around.
After some verbs of perception:
We saw the children cross the street.
In this sentence, cross the street describes the action we witnessed.
The verb help can take either form:
She helped me carry the boxes.
She helped me to carry the boxes.
Both are grammatical.
The base form also appears in other constructions. In Open the door, for example, open is the main verb of a command. It is not an infinitive complement following another verb.
Other Infinitive Forms
Infinitives can also express negation, voice, and relationships between events.
| Form | Example | What it expresses |
|---|---|---|
| Negative | not to interrupt | Negation of the infinitive action |
| Passive | to be repaired | The relevant subject undergoes the action |
| Perfect | to have completed the work | Completion before another reference point |
| Continuous | to be working | An ongoing activity |
For example:
Maya appears to have forgotten the appointment.
The forgetting is understood to have happened before the present assessment expressed by appears.
In a negative infinitive, not normally comes before to:
The teacher reminded us not to touch the equipment.
An adverb can also appear between to and the verb:
They decided to carefully examine the evidence.
This is called a split infinitive. It is not automatically incorrect. The placement is acceptable when it makes the sentence natural and clear.
When To Is Not an Infinitive Marker
Not every occurrence of to introduces an infinitive.
Sometimes to is a preposition followed by a noun phrase or an -ing construction. It can even appear before a word that looks like a base verb but functions as a noun.
To Before a Base Verb or Noun
Compare:
She wants to work from home.
Here, work is a verb, and to work is an infinitive.
The journey to work takes an hour.
In this sentence, work functions as a noun referring to a workplace. To is a preposition.
The words are spelled the same way, but their grammatical roles differ.
To Before a Noun or Pronoun
We sent the invitation to the coordinator.
The word to is a preposition followed by the noun phrase the coordinator. The highlighted group does not contain an infinitive.
To Before an -ing Construction
Consider:
We hope to meet the team.
We look forward to meeting the team.
In the first sentence, to meet is an infinitive.
In the second, to is a preposition belonging to look forward to. It takes the -ing construction meeting the team as its complement.
Another example:
He is committed to improving his writing.
Here, to is also a preposition.
Used to vs. Be Used to
These expressions have different meanings and grammatical patterns.
She used to work late.
Used to + base verb describes a past habit or state.
She is used to working late.
Be used to + -ing form means she is accustomed to working late.
In the second sentence, to is a preposition followed by an -ing construction.
To distinguish these patterns, look at the grammatical function of the word following to and how the entire expression works in the sentence.
Practice Questions
When examining an infinitive construction, consider its complete structure, its function in the sentence, and who is understood to perform its action.
The following questions test these distinctions.
1. To complete the project on time requires careful planning.
What is the function of the highlighted infinitive phrase?
2. The students visited the laboratory to observe the experiment.
Does the highlighted phrase complete the meaning of visited or express purpose?
3. Mia persuaded Oliver to join the discussion.
Who is understood to join the discussion?
4. The assistant has several documents to review before lunch.
Are the documents performing the action of reviewing, or are they the things being reviewed?
5. The journey to work takes an hour.
Does the highlighted group contain an infinitive?
6. The instructor made the participants repeat the exercise.
What form of infinitive appears in the highlighted group?
7. To finish the inspection, the engineer requested another hour.
Why is a comma appropriate after the highlighted phrase?
8. The team agreed to inspect the building and to submit a report by Friday.
How many infinitive constructions are highlighted, and who is understood to perform their actions?
Answers and Explanations
1. Subject. To complete the project on time functions as the subject of requires. The entire activity requires careful planning.
2. Purpose. To observe the experiment explains why the students visited the laboratory.
3. Oliver. Oliver is understood to join the discussion. Mia is the person persuading him.
4. The documents are being reviewed. The infinitive phrase modifies documents. The documents are the things that need reviewing, not the people performing the action.
5. No. To work is a prepositional phrase here. Work functions as a noun meaning the workplace or place of employment.
6. Bare infinitive. Repeat the exercise contains the base verb repeat without to. It follows made in a causative construction.
7. It expresses purpose. The introductory infinitive phrase explains why the engineer requested another hour. A comma separates that introductory information from the main clause.
8. Two infinitive constructions. They are to inspect the building and to submit a report by Friday. Both complete the meaning of agreed, and the team is understood to perform both actions.
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