The infinitive is a non-finite form of a verb that is not marked by tense or subject agreement. In English, the infinitive typically appears with “to” (e.g., “to run,” “to speak,” “to be”), though certain constructions and verbs use infinitives without “to” (also known as the bare infinitive). Infinitives are versatile and can function in various ways within sentences, including as nouns, adjectives, and adverbs.
Table of contents
What Is an Infinitive?
An infinitive is the base form of a verb often preceded by “to.” It does not show tense, person, or number. The infinitive form of a verb is frequently listed in dictionaries (e.g., “to go,” “to see,” “to eat”).
Examples of Infinitives:
- to walk
- to read
- to understand
- to be
- to have
When used in a sentence, an infinitive can serve a variety of roles, such as expressing purpose, indicating what someone wants or intends to do, or modifying other parts of the sentence.
Types of Infinitives
Infinitives can be broadly divided into two main types:
1. Full Infinitive
Full infinitives (the base form of a verb preceded by “to”) are used in several grammatical situations. These situations often depend on the structure of the sentence, the verb, or the intended meaning. Below is a detailed explanation of when and why full infinitives are used, along with examples for clarity.
After Certain Verbs
Some verbs are always followed by a full infinitive when they take another verb as their complement. These verbs often express intention, willingness, decision, or effort.
Examples:
- He promised to help with the project.
- She decided to leave early.
- They managed to complete the task on time.
Here’s a list of verbs that always use the full infinitive if they are followed by another verb form. These verbs can still be used without an infinitive, but if they use one, it must be the full infinitive:
- Agree
- Appear
- Arrange
- Ask
- Attempt
- Beg
- Choose
- Consent
- Decide
- Demand
- Deserve
- Expect
- Fail
- Happen
- Hope
- Intend
- Learn
- Manage
- Need
- Offer
- Plan
- Prepare
- Pretend
- Promise
- Refuse
- Resolve
- Seem
- Swear
- Tend
- Threaten
- Volunteer
- Wait
- Want
- Wish
- Yearn
To Indicate Purpose (Infinitive of Purpose)
The full infinitive is often used to explain why someone does something or to express the purpose of an action.
Examples:
- He went to the store to buy groceries.
(The purpose of going to the store is to buy groceries.) - She studies hard to get good grades.
- They left early to avoid traffic.
After Adjectives
Full infinitives are commonly used after adjectives to explain the subject’s feelings, opinions, or attitudes.
Examples:
- She is eager to learn new things.
- It’s difficult to understand his handwriting.
- I’m happy to help you with your project.
After Nouns (to Describe or Qualify the Noun)
The full infinitive can follow a noun to describe it further or specify its purpose.
Examples:
- She has a lot of work to do today.
(The purpose of the work is to be completed.) - This is a great book to read on vacation.
- We need a plan to solve this problem.
To Express Intentions or Expectations (Subject of the Sentence)
Full infinitives are used to express intentions, expectations, or goals and can act as the subject of a sentence.
Examples:
- To travel around the world is my dream.
- To understand quantum physics requires patience.
- To eat healthy is important for good health.
After “Question Words” (Interrogative Words)
When question words like what, where, how, when, etc., are followed by a verb, the full infinitive is used.
Examples:
- He doesn’t know what to say in the interview.
- Can you tell me how to get to the train station?
- I’m unsure where to go from here.
After Certain Verbs with Objects
Some verbs require an object followed by a full infinitive.
Examples:
- She advised me to take the job.
- They encouraged her to try again.
- The teacher allowed us to leave early.
In Expressions with “It” as the Subject
The full infinitive is often used with the construction it + to be + adjective to form impersonal expressions.
Examples:
- It’s important to follow the rules.
- It’s easy to make this mistake.
- It’s nice to meet you.
To Modify or Clarify “Too” or “Enough”
The full infinitive is used after too or enough to explain why something is excessive or sufficient.
Examples:
- He’s too tired to work today.
(Excessive tiredness prevents working.) - She’s old enough to vote now.
(She is sufficiently old to vote.)
After Phrases Like “In Order To” and “So As To”
Full infinitives are used after these phrases to indicate purpose in a more formal way.
Examples:
- He left early in order to catch the train.
- She speaks slowly so as to be understood.
In Certain Fixed Expressions
Some idiomatic or formal expressions always use full infinitives.
Examples:
- To be honest, I didn’t like the movie.
- To sum up, we need better planning.
In Reported Speech
Full infinitives are often used in reported speech when the original statement involves a verb like agree, decide, offer, or promise.
Examples:
- Direct Speech: “I’ll help you,” she said.
Reported Speech: She promised to help me.
As a Complement to Certain Words
Some verbs, adjectives, or nouns are naturally paired with a full infinitive to complete their meaning.
Examples:
- I hope to see you soon.
(Verb complement) - This is a great opportunity to learn something new.
(Noun complement) - She was reluctant to speak in public.
(Adjective complement)
Key Takeaways:
- The full infinitive is versatile and used in various grammatical contexts.
- It often indicates purpose, intent, or the reason behind an action.
- It’s frequently paired with certain verbs, adjectives, and nouns to clarify or complete meaning.
2. Bare Infinitive
A bare infinitive (the base form of a verb without “to”) is used in specific grammatical situations. These cases often depend on the structure of the sentence, the preceding word, or the function of the verb. Here’s a detailed breakdown of when and why bare infinitives are used, along with examples for each situation:
After Modal Verbs
Modal verbs like can, could, may, might, shall, should, will, would, must, and ought to are always followed by a bare infinitive.
Examples:
- She can sing beautifully.
- You must finish your homework before dinner.
- He should call his parents.
After Auxiliary Verbs (Helping Verbs)
The bare infinitive is used after the auxiliary verbs do, does, and did in negative sentences, questions, and emphatic statements.
Examples:
- Do you know the answer?
- She doesn’t like coffee.
- I did try to help him.
After “Let,” “Make,” “See,” “Hear,” and Similar Verbs
Certain causative and perception verbs are followed by a bare infinitive when referring to the completion of an action.
Examples:
- Let him go now.
- She made me apologize for my mistake.
- I heard him sing a beautiful song.
In Conditional Clauses with “If” and “Should”
In formal or inverted conditional sentences, a bare infinitive is used after “should.”
Examples:
- If he should call, let me know.
- Should you need assistance, don’t hesitate to ask.
After “Had Better,” “Would Rather,” and “Sooner”
Expressions like had better, would rather, and sooner require a bare infinitive after them.
Examples:
- You had better study for the exam.
- I would rather stay home tonight.
- She’d sooner leave than argue.
After “Why” in Questions
When asking a question starting with why, the bare infinitive is used.
Examples:
- Why wait until tomorrow?
- Why not ask him directly?
In Parallel Structures with Coordinating Conjunctions
In some cases, a bare infinitive is used to avoid repetition after a modal or auxiliary verb in a parallel structure.
Examples:
- He can run but not hide.
- She didn’t study, nor did she pass the exam.
After “Help” (Optional Bare Infinitive)
The verb help can be followed by either a full or bare infinitive, but the bare infinitive is common in informal contexts.
Examples:
- Can you help me carry these boxes?
- She helped him prepare for the test.
In Passive Constructions with Causative Verbs
In passive constructions involving causative verbs like make, the bare infinitive is used.
Examples:
- He was made apologize for his mistake.
- They were let go early.
After Certain Expressions or Fixed Phrases
Some idiomatic expressions or fixed phrases use the bare infinitive.
Examples:
- All I did was ask a simple question.
- What you must do is wait patiently.
In Direct Commands or Imperatives
The imperative mood uses the bare infinitive to give commands or instructions.
Examples:
- Open the door.
- Stop talking.
- Please be quiet.
After “Do Nothing But”
The bare infinitive follows phrases like do nothing but to indicate exclusive actions.
Examples:
- He does nothing but complain all day.
- She did nothing but watch TV.
How Do You Use Infinitives?
Although we’ve already discussed the primary uses of both infinitive forms, there are still some important aspects of infinitive grammar to explore. Below, we’ll break down three key areas to deepen your understanding: split infinitives, passive infinitives, and continuous infinitives.
1. Split Infinitives
A split infinitive occurs when an adverb or other word is inserted between “to” and the base form of the verb in a full infinitive. While some traditional grammar rules discourage split infinitives, they are widely accepted in modern English when they improve clarity or flow.
Examples:
- She promised to never give up.
(The adverb “never” splits “to” and “give.”) - We need to fully understand the problem before proceeding.
(The adverb “fully” splits the infinitive.)
When to Use:
- To emphasize or clarify meaning.
- To improve sentence flow, especially in informal contexts.
Avoidance (if required):
- She promised never to give up. (Avoided split infinitive.)
- We need fully to understand the problem. (Reworded to avoid splitting.)
2. Passive Infinitives
A passive infinitive is used when the subject of the sentence is the receiver of the action, not the doer. It takes the form of “to be + past participle”.
Examples:
- The proposal needs to be reviewed by the committee.
(The action is “reviewing,” and the subject will receive the action.) - She wants to be invited to the event.
(She is not inviting; she will be invited.)
When to Use:
- In passive voice constructions to shift the focus to the object or the action rather than the subject.
- To emphasize the action rather than the doer.
Active vs. Passive Comparison:
- Active: The manager promised to review the proposal.
- Passive: The proposal needs to be reviewed by the manager.
3. Continuous Infinitives
A continuous infinitive describes an action that is ongoing or happening at the same time as another action. It takes the form of “to be + present participle” (the “-ing” form of a verb).
Examples:
- He seems to be sleeping right now.
(The action of “sleeping” is in progress.) - They are happy to be working on such an exciting project.
(The action of “working” is ongoing.)
When to Use:
- To show that an action is happening simultaneously with another event or state.
- To indicate an ongoing state or activity.
Comparison with Simple Infinitive:
- Simple Infinitive: He seems to sleep well at night.
(Focuses on the general action, not the ongoing state.) - Continuous Infinitive: He seems to be sleeping now.
(Focuses on the action in progress.)
| Type | Form | Function | Example |
|---|---|---|---|
| Split Infinitives | “to + adverb + verb” | Adds emphasis or clarity, especially in informal speech. | She decided to quickly leave the room. |
| Passive Infinitives | “to be + past participle” | Focuses on the action done to the subject (receiver of the action). | The report needs to be written by tomorrow. |
| Continuous Infinitives | “to be + present participle” | Indicates an action in progress or happening simultaneously with another action or state. | He seems to be studying for the exam. |
Infinitives vs. prepositional phrases
Infinitives and prepositional phrases can both start with the word “to,” which sometimes causes confusion. However, they serve entirely different purposes in a sentence.
An infinitive is the base form of a verb, often preceded by “to.” It functions as a noun, adjective, or adverb in a sentence. While a prepositional phrase begins with a preposition (e.g., to, in, on, by, with) and ends with a noun or pronoun (the object of the preposition). It functions as an adjective or adverb, describing time, place, direction, or manner.
How to Tell the Difference
The simplest way to identify whether “to” introduces an infinitive or a prepositional phrase is to look at the word that follows it:
- If “to” is followed by a verb, it’s an infinitive.
- He loves to read novels. (Read is a verb → infinitive.)
- If “to” is followed by a noun or pronoun, it’s a prepositional phrase.
- He walked to the library. (Library is a noun → prepositional phrase.)
Common Infinitive Errors to Avoid
- Infinitive vs. Gerund (to do vs. doing): Some verbs prefer infinitives while others prefer gerunds. This can vary by verb:
- Prefer infinitive: “They decided to leave.”
- Prefer gerund: “They enjoy traveling.”
- Split Infinitives: Placing an adverb between “to” and the verb (e.g., “to quickly run”) is called a split infinitive. It’s not grammatically incorrect, but some prefer avoiding it in formal writing.
- Acceptable: “She decided to quickly leave.”
- More Formal: “She decided to leave quickly.”
- Forgetting to use the bare infinitive when required: After modal verbs, do not insert “to.”
- Incorrect: “He can to swim.”
- Correct: “He can swim.”