Infinitives and Infinitive Phrases

What Is an Infinitive?

An infinitive is the base form of a verb, usually preceded by the particle "to." It is not limited by person, number, or tense, which is why it is called "non-finite." Infinitives can function as noun, adjective, or adverb within a sentence, making them one of the most versatile verb forms in English.
To-infinitive: the most common form — "to" + base verb (e.g., to read, to swim, to understand)
Bare infinitive: the base verb without "to" (e.g., read, swim, understand), used after certain verbs and structures
Non-finite nature: infinitives do not show tense, person, or number — they are not the main verb of a clause

Forms of the To-Infinitive

The simple to-infinitive is "to" + base verb. This is the default infinitive form and appears in a wide range of sentence structures. It can follow certain verbs, adjectives, and nouns, or stand on its own as a complement.
Simple infinitive: to go, to write, to think — the base form most students encounter first
Perfect infinitive: to have gone, to have written — formed with "to have" + past participle, expressing completed action relative to the main verb
Passive infinitive: to be seen, to be written — formed with "to be" + past participle
Perfect passive infinitive: to have been seen — combines both perfect and passive meanings

To-Infinitive Forms Summary

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Simple: to + verb → to walk
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Perfect: to have + past participle → to have walked
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Passive: to be + past participle → to be walked
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Continuous: to be + -ing → to be walking
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Perfect continuous: to have been + -ing → to have been walking
A bare infinitive is the base verb without "to." It appears after modal verbs, after certain causative and perception verbs, and in a few fixed expressions. Recognizing where "to" is omitted is essential for grammatical accuracy.
After modals: can go, should study, must leave — modal verbs are always followed by bare infinitives
After causative verbs (make, let, have): She made him cry, Let me explain, I had him fix the car
After perception verbs (see, hear, feel, watch, notice): I saw her leave, We heard him sing — when describing a completed action
After "had better" and "would rather": You had better study, I would rather stay
After "do" in emphatic structures: I do believe you, She does want to come

Infinitive Functioning as a Noun

When an infinitive acts as a noun, it can serve as the subject of a sentence, a direct object, a subject complement, or an appositive. In every case, the infinitive or infinitive phrase names an action or state that is itself being talked about.
Subject: To travel is her greatest ambition. — The infinitive phrase names the thing being discussed.
Direct object: He wants to become a doctor. — The infinitive phrase receives the action of the main verb.
Subject complement: Her goal is to win the championship. — The infinitive phrase renames or describes the subject.
Appositive: His one desire, to succeed, drove him forward. — The infinitive phrase restates the noun before it.
English frequently uses a dummy subject "it" to postpone a long infinitive phrase to the end of the sentence. This structure keeps sentences readable and is very common in formal writing.
Pattern: It + linking verb + adjective/noun + to-infinitive phrase
Example: It is important to submit the assignment on time. → "It" is a dummy subject; the real subject is "to submit the assignment on time."
Example: It was generous of her to donate the money. → The real subject is the infinitive phrase.
Why it matters: The postponed infinitive avoids awkward front-loaded sentences like To submit the assignment on time is important.

Infinitive Functioning as an Adjective

When an infinitive functions as an adjective, it modifies a noun or pronoun, answering the question "which one?" or "what kind?" The infinitive always follows the noun it modifies.
Modifying a noun: She has a lot of work to do. → "to do" modifies "work" — which work? the work to do.
Modifying a pronoun: I need something to eat. → "to eat" modifies "something" — which thing? something to eat.
After ordinal numbers: He was the first to arrive. → "to arrive" modifies "the first."
After superlatives: This is the best book to read on the topic. → "to read" describes which book.

Adjectival Infinitive Examples

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I have no desire to argue. — "to argue" modifies "desire"
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She is the person to ask. — "to ask" modifies "person"
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The time to act is now. — "to act" modifies "time"
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There are many challenges to overcome. — "to overcome" modifies "challenges"
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He is not a man to trust easily. — "to trust" modifies "man"

Infinitive Functioning as an Adverb

When an infinitive functions as an adverb, it modifies a verb, an adjective, or another adverb. It typically answers "why?", "for what purpose?", or "to what extent?" This is the most common function of infinitives in everyday English.
Purpose: She studies hard to pass the test. → "to pass the test" answers why she studies — adverb of purpose.
After adjectives: He is eager to learn. → "to learn" modifies the adjective "eager" — answers eager about what?
Result: He lived to be ninety. → "to be ninety" expresses the result or outcome of living.
Condition: To hear him talk, you would think he owns the world. → "To hear him talk" sets a hypothetical condition.

Adverbial Infinitive — Common Patterns

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Purpose: I went to the store to buy milk. (why?)
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After adjective: She was reluctant to leave. (reluctant about what?)
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After noun + be: The house is to let. (available for what?)
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Comparison: She is quick to judge. (quick at what?)

Infinitive Phrases and Their Structure

An infinitive phrase consists of an infinitive plus any modifier, complement, or object that goes with it. The entire phrase functions as a single unit — as a noun, adjective, or adverb — just like the infinitive alone.
Structure: to + verb + object/complement/modifiers → to write a novel in one year
With an object: to eat pizza — "pizza" is the object of the infinitive "to eat."
With an adverb: to run quickly — "quickly" modifies the infinitive "to run."
With a prepositional phrase: to study in the library — "in the library" adds detail to the infinitive.
Recognizing the boundaries of an infinitive phrase is key to identifying its function in sentence structure. The phrase begins with "to" (or the bare infinitive after modals/causatives) and extends through all attached words.
Noun phrase: To become a skilled surgeon requires years of training. — Entire phrase "to become a skilled surgeon" = subject.
Adjective phrase: The decision to cancel the event upset many people. — "to cancel the event" modifies "decision."
Adverb phrase: He stayed behind to help the injured player. — "to help the injured player" answers why he stayed.

Identifying Function — Quick Reference

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Noun: replace with "it" → It requires years of training ✓
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Adjective: ask "which noun?" → Which decision? The decision to cancel the event ✓
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Adverb: ask "why?" or "for what purpose?" → Why did he stay? To help the injured player ✓

Split Infinitives

A split infinitive occurs when a word or phrase appears between "to" and the base verb (e.g., to boldly go). While traditional prescriptive grammar discouraged split infinitives, modern English — especially in speech and informal writing — accepts them when they improve clarity or sound natural.
Traditional rule: Avoid placing any word between "to" and the verb — to go boldly instead of to boldly go.
Modern practice: Splitting is acceptable and often preferred when the alternative is awkward — to really understand sounds more natural than really to understand.
When to avoid splitting: In formal academic writing, keep the infinitive intact unless splitting significantly improves clarity.
When splitting is better: She decided to gradually reduce her workload — moving "gradually" elsewhere creates awkwardness.

Verbs That Take Infinitives

Many verbs are followed directly by a to-infinitive as their direct object or complement. Knowing which verbs take infinitives (vs. gerunds or both) is critical for sentence construction. Some verbs can take either form with a change in meaning.
Verbs + to-infinitive: want, hope, decide, plan, agree, refuse, offer, promise, choose, expect, pretend, manage, fail, learn, deserve, need, appear, seem, tend
Verbs + bare infinitive: can, could, will, would, shall, should, may, might, must (modals); make, let, have (causatives); see, hear, feel, watch, notice (perception verbs)
Verbs + either infinitive or gerund (no meaning change): begin, start, continue, like, love, hate, prefer, intend, attempt
Verbs + either infinitive or gerund (meaning change): remember, forget, stop, try, regret, go on — these are high-yield distinctions

Verbs With Different Infinitive vs. Gerund Meanings

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Stop to think (pause in order to think) vs. Stop thinking (cease the act of thinking)
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Remember to call (remember, then call) vs. Remember calling (recall a past call)
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Try to open (attempt, possibly fail) vs. Try opening (experiment with opening)
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Forget to lock (failed to lock) vs. Forget locking (locked but have no memory of it)
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Regret to inform (feel regretful about what you are about to do) vs. Regret informing (feel regretful about what you already did)