Infinitives can be confusing because they do not all look alike. To leave is an infinitive, but so is leave after a modal in should leave. You may also come across longer forms such as to be invited and to have finished.
The pattern becomes clearer when you separate the infinitive form from the structure around it. Infinitives are non-finite, and English can use them with or without to in several common grammatical patterns.
What Is an Infinitive?
An infinitive is a non-finite verb form used in a range of grammatical constructions.
English commonly distinguishes:
- to-infinitive: to write, to leave, to understand
- bare infinitive: write, leave, understand
For example:
Maya wants to leave.
To leave is a to-infinitive.
Maya should leave.
Leave is a bare infinitive after the modal auxiliary should.
The bare infinitive has the same form as the base form of the verb. Calling it a bare infinitive describes how that base form is being used in the particular sentence.
Infinitives do not independently show ordinary tense or subject agreement. Those relationships come from the larger grammatical structure.
To-Infinitive vs. Bare Infinitive
The basic difference is whether to is present.
To-Infinitive
The common pattern is:
to + base form
to read
to work
to travel
to explain
Noah hopes to travel next year.
Bare Infinitive
A bare infinitive appears without to.
Noah can travel next year.
You must wait here.
Let Ava speak.
The lexical verbs travel, wait, and speak have the same shape as their base forms, but the surrounding structures license their use as bare infinitives.
Infinitives Are Non-Finite
A finite verb can show tense or agreement with its subject.
She works every Saturday.
Works is finite and agrees with the third-person singular subject she.
Compare:
She wants to work every Saturday.
They want to work every Saturday.
To work does not change when the subject changes.
The finite verb changes from wants to want, while the infinitive remains the same.
This is what is meant when an infinitive is described as non-finite.
To-Infinitives After Verbs
Many verbs commonly take a to-infinitive complement.
Typical patterns include:
- agree to do
- decide to do
- expect to do
- hope to do
- learn to do
- manage to do
- need to do
- plan to do
- promise to do
- refuse to do
- want to do
Ava decided to stay.
Daniel hopes to finish early.
Priya managed to solve the problem.
Marcus refused to answer.
Nina promised to call later.
The infinitive completes or expands the meaning of the first verb.
Different verbs allow different complement patterns, so not every verb can be followed by a to-infinitive in the same way.
Verb + Object + To-Infinitive
Some verbs allow an object between the first verb and the infinitive.
The pattern is:
verb + object + to-infinitive
The teacher asked Leo to wait.
Maya reminded her sister to call.
We expected the train to arrive on time.
The doctor advised Noah to rest.
Priya encouraged Ava to apply.
In these examples, the object is also understood as the subject of the infinitive.
In:
The teacher asked Leo to wait.
Leo is the person who is expected to wait.
Common verbs in this pattern include:
- advise
- allow
- ask
- encourage
- expect
- invite
- remind
- tell
- want
- warn
The complete construction matters because not every verb that takes a to-infinitive also allows an object before it.
Bare Infinitives After Modal Verbs
Modal auxiliaries are followed by a bare infinitive.
You should leave now.
Maya can swim.
We might arrive late.
Daniel must finish today.
They will call tomorrow.
The lexical verbs leave, swim, arrive, finish, and call are bare infinitives.
The modal carries meanings such as possibility, necessity, willingness, or prediction, while the following lexical verb remains in its base form.
This is one of the clearest reasons infinitive should not be defined simply as “to + verb.”
Bare Infinitives After Make, Let, and Help
Bare infinitives also occur in several other common constructions.
After Make
The joke made everyone laugh.
The delay made us change our plans.
The pattern is:
make + object + bare infinitive
After Let
Let Maya speak.
They let the children play outside.
The pattern is:
let + object + bare infinitive
After Help
Both a bare infinitive and a to-infinitive are standard after help.
Ava helped me carry the boxes.
Ava helped me to carry the boxes.
Both forms are grammatical. The version without to is especially common.
Bare Infinitives After Perception Verbs
Perception verbs such as see, hear, watch, feel, and notice can occur with:
perception verb + object + bare infinitive
I saw Maya cross the street.
We heard the door slam.
Theo watched the bird land on the fence.
The bare infinitive can present the perceived event more as a whole.
These verbs can also occur with an object followed by an -ing form:
I saw Maya crossing the street.
We heard someone knocking upstairs.
The -ing form tends to present the activity from within or as it is unfolding.
The distinction is therefore not one of correct versus incorrect grammar. The two constructions can present the same situation from different perspectives.
Infinitives After Adjectives
To-infinitives commonly occur after adjectives.
Maya was happy to help.
Ethan is ready to leave.
The instructions were difficult to understand.
We were surprised to hear the news.
The infinitive completes or develops the meaning expressed by the adjective.
Common patterns include:
pleased to meet
eager to begin
likely to happen
difficult to explain
ready to start
Adjective + for + Noun or Pronoun + To-Infinitive
The subject associated with an infinitive can sometimes be stated explicitly with for.
It was difficult for Maya to hear the speaker.
It is unusual for the shop to close this early.
This task is easy for children to understand.
In each sentence, the noun phrase after for identifies who or what is associated with the infinitive situation.
Infinitives After Nouns and Pronouns
A to-infinitive can add information after a noun.
We had an opportunity to talk.
There is no need to hurry.
Maya made a decision to stay.
The team developed a plan to reduce costs.
The infinitive helps specify or complete the meaning of the noun.
Infinitives also commonly follow indefinite pronouns.
I need something to read.
She had no one to ask.
We found nothing to worry about.
Is there anything to eat?
These structures are common in everyday English and do not require a separate finite clause.
Infinitives of Purpose
A to-infinitive can explain why someone performs an action.
Ava went outside to make a phone call.
The reason she went outside was to make the call.
Liam opened the window to let in fresh air.
Priya saved money to buy a new laptop.
Marcus left early to avoid the traffic.
This use differs from an infinitive selected as the complement of a verb.
Compare:
Priya wants to buy a new laptop.
To buy complements wants.
Now:
Priya saved money to buy a new laptop.
Here, to buy expresses the purpose of saving the money.
The infinitive form is the same, but its relationship to the main clause is different.
Negative Infinitives
A to-infinitive is commonly made negative by placing not before it.
not + to-infinitive
Maya decided not to go.
Daniel promised not to tell anyone.
We agreed not to discuss the issue yet.
Nina chose not to respond.
The negative applies to the infinitive situation.
Negative purpose can also be made explicit with expressions such as:
She spoke quietly so as not to wake the baby.
He left early in order not to miss the train.
These longer structures are especially useful when the negative purpose needs to be unmistakable.
Passive Infinitives
A passive to-infinitive commonly uses:
to be + past participle
Maya expects to be invited.
The documents need to be signed.
Noah would prefer to be driven.
The building is expected to be completed next year.
The subject is presented as receiving the action rather than performing it.
Compare:
Ava hopes to invite Noah.
Active infinitive.
Ava hopes to be invited.
Passive infinitive.
A passive infinitival structure can also occur without to when the surrounding grammar requires a bare infinitive:
The documents must be signed today.
Here, be signed follows the modal must.
Perfect Infinitives
A perfect to-infinitive commonly uses:
to have + past participle
She seems to have forgotten the appointment.
They appear to have left early.
I am glad to have met you.
Marcus claims to have finished the work.
The perfect infinitive typically presents its situation as earlier than the reference point established by the larger sentence.
Compare:
Maya seems to know the answer.
The knowing is presented as current relative to seems.
Maya seems to have known the answer.
The knowing is presented as belonging to an earlier time relative to that reference point.
The infinitive itself remains non-finite. The larger clause establishes the broader time relationship.
Perfect Passive Infinitives
Perfect and passive structure can combine.
The common to-infinitive pattern is:
to have been + past participle
The documents appear to have been misplaced.
The road seems to have been repaired recently.
Maya is believed to have been selected for the role.
The construction combines perfect meaning with passive voice: the infinitive situation is presented as earlier, and its subject receives the action.
Progressive Infinitives
An infinitive can also have progressive structure.
The common pattern is:
to be + -ing form
Maya seems to be working from home.
The children appear to be sleeping.
Noah claims to be studying.
The progressive form presents the situation as ongoing relative to the larger clause.
Compare:
Leo seems to work from home.
with:
Leo seems to be working from home.
The second sentence presents the working more clearly as an activity in progress.
Progressive structure can also follow a modal as a bare infinitive construction:
Leo may be working from home today.
Perfect Progressive Infinitives
Perfect and progressive structure can be combined:
to have been + -ing form
Maya seems to have been working all morning.
The company appears to have been expanding rapidly.
Noah claims to have been waiting for an hour.
The construction presents an activity as extending over a period before or up to the reference point supplied by the larger sentence.
Like other infinitives, it remains non-finite despite containing perfect and progressive structure.
What Is an Infinitive Phrase?
Traditional classroom grammar commonly uses the term infinitive phrase for an infinitive together with the words that belong with it.
For example:
to finish the report before lunch
The expression contains:
- to finish = infinitive
- the report = object of finish
- before lunch = additional modifier
In:
Maya hopes to finish the report before lunch.
the whole infinitive expression functions as a complement of hopes.
Modern grammatical descriptions may call structures like these infinitival clauses because they contain a non-finite verb and can have internal clause structure.
The terminology differs, but both approaches recognize that the complete expression may contain much more than to + verb.
Can an Infinitive Have Its Own Subject?
An infinitive often has an understood subject.
Maya wants to leave.
Maya is understood as the person who will leave.
The subject can also be expressed in the larger construction.
Maya wants Noah to leave.
Noah is understood as the subject of to leave.
Another common pattern uses for:
It is important for everyone to arrive on time.
Everyone is associated with the infinitive to arrive.
Understanding the subject relationship helps explain why infinitival structures are more than isolated verb forms.
Split Infinitives
A split infinitive occurs when a word, usually an adverb, appears between to and the base verb.
to carefully check
to fully understand
to gradually improve
Split infinitives are grammatical in standard modern English.
Please remember to carefully check every figure.
The adverb carefully appears between to and check, and there is no grammatical problem with that placement.
Sometimes another position is equally natural:
Please remember to check every figure carefully.
In other cases, keeping the adverb inside the infinitive can make the intended meaning or emphasis clearer.
The company plans to gradually reduce its expenses.
Automatically moving gradually elsewhere does not necessarily improve the sentence.
A particular publication or style guide may prefer another placement in some contexts, but a split infinitive is not inherently incorrect.
Infinitive vs. Gerund
Some verbs commonly take a to-infinitive:
decide to leave
hope to return
Others take an -ing complement:
enjoy reading
avoid driving
Some allow both:
start working
start to work
And with certain verbs, changing the form can change the meaning:
stop smoking
stop to smoke
These differences belong to verb-complement patterns rather than to the definition of an infinitive itself.
How to Identify an Infinitive
Start with the form, then look at the surrounding grammar.
Look for To + Base Verb
to read
to leave
to understand
But make sure to is actually introducing an infinitive.
Compare:
Maya wants to travel.
To travel is a to-infinitive.
Maya looks forward to traveling.
Here, to is a preposition, not an infinitive marker.
Look for a Bare Infinitive
After a modal:
You should wait.
After let:
Let him speak.
After make:
The film made us laugh.
Check the Infinitive’s Relationship to the Sentence
Verb complement:
Nina hopes to return.
Purpose:
Nina left early to catch the train.
Modifier after a noun:
Nina has a report to finish.
Complement after an adjective:
Nina is ready to begin.
The infinitive form may be similar in each case, but its grammatical relationship with the surrounding sentence changes.
Infinitive Examples in Sentences
Olivia plans to move next year.
To move complements plans.
The coach encouraged Daniel to continue.
Daniel is understood as the subject of to continue.
You must wear a helmet.
Wear is a bare infinitive after must.
The joke made everyone smile.
Smile is a bare infinitive after made + object.
I watched the bird fly across the lake.
Fly is a bare infinitive after a perception verb.
Maya was delighted to receive the invitation.
To receive follows the adjective delighted.
We need a place to stay.
To stay adds information about place.
Noah went downstairs to answer the door.
To answer expresses purpose.
Priya decided not to attend the meeting.
Not to attend is a negative infinitive.
The package is expected to be delivered tomorrow.
To be delivered is a passive infinitive.
Daniel appears to have forgotten his password.
To have forgotten is a perfect infinitive.
The children seem to be enjoying the performance.
To be enjoying is a progressive infinitive.
The road appears to have been closed overnight.
To have been closed is a perfect passive infinitive.
Ava hopes to finish the assignment before dinner.
The complete infinitive expression functions as a complement of hopes.
An infinitive is a non-finite verb form that can appear with or without to. Infinitives occur in verb-complement patterns, after adjectives and nouns, in expressions of purpose, and in passive, perfect, progressive, and negative structures.
The form does not independently carry ordinary tense or subject agreement. Looking at the larger grammatical construction tells you how the infinitive relates to its subject, time reference, voice, and meaning.
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