Infinitives: Form, Function, and Usage

An infinitive is the base form of a verb, usually preceded by the particle to (to + base verb). Unlike gerunds, which function exclusively as nouns, infinitives are far more flexible: they can act as nouns, adjectives, or adverbs. They are essential for expressing intentions, purposes, desires, and future actions — often adding a layer of goal-oriented meaning to your sentences.

1. The Two Types of Infinitives

• Full Infinitive (to + base verb):
  “She wants to go home.”
• Bare Infinitive (base verb without to): Used after modals, certain verbs of perception, and the verbs let, make, help (in some cases).
  “You must leave now.” / “I saw him enter the building.”

2. The Three Core Functions of Infinitives

Because infinitives are non-finite verb forms (they do not change for tense or person), they can occupy several grammatical roles without being the main verb of the clause.

A. Infinitive as a Noun (Subject, Object, Subject Complement)

As a noun, the infinitive names an action or state, often with a sense of potential or intention.

• Subject: “To travel the world is my dream.” (More formal; a gerund is often preferred in everyday speech.)
• Direct Object: “They decided to postpone the trip.”
• Subject Complement: “His only goal is to win the championship.”

B. Infinitive as an Adjective (Modifying a Noun)

When used adjectivally, the infinitive modifies a noun, often explaining what the noun is for or what should be done with it.

• “I need a book to read on the plane.” (Describes the book.)
• “She has a lot of work to finish.”
• “There is nothing to fear.”

C. Infinitive as an Adverb (Modifying a Verb, Adjective, or Whole Clause)

The most common adverbial use is to express purpose (in order to). It can also express result or reason.

• Purpose: “He went to the store to buy milk.”
• Result: “She woke up to find the house empty.”
• Reason (after adjectives): “I am happy to hear that news.”

3. Verbs That Are Always Followed by an Infinitive

Many common verbs require an infinitive as their direct object. These verbs often express intention, desire, planning, or decision — a future orientation.

4. Infinitives with "Too" and "Enough"

Infinitives are often used with the degree adverbs too (meaning "excessively") and enough (meaning "sufficiently"). This structure is always: too + adjective/adverb + (for someone) + infinitive, or adjective/adverb + enough + infinitive.

• “The soup is too hot to eat right now.”
• “She is old enough to vote.”
• “This box is too heavy for me to lift.”
• “He ran fast enough to catch the bus.”

5. The Bare Infinitive (Without "To")

The bare infinitive (base form without to) is used in specific contexts:

• After modal verbs (can, could, may, might, must, shall, should, will, would):
  “You must go now.” / “I will call you.”
• After verbs of perception (see, hear, watch, notice, feel) when the action is perceived as a complete event:
  “I saw her leave the building.” (I saw the whole action.)
• After let and make (causative verbs):
  “She let him borrow her car.” / “He made me laugh.”
• After would rather, had better, had sooner:
  “I would rather stay home.” / “You had better leave now.”
• After help (the infinitive can be bare or with to, both are correct):
  “She helped me (to) finish the project.”

6. Advanced Infinitive Forms

Like gerunds, infinitives have additional forms to express time and voice, allowing for more precise descriptions.

A. Passive Infinitive (To Be + V3)

Use this when the action of the infinitive happens to the subject/object of the main clause.

• “She hopes to be invited to the party.”
• “This needs to be done immediately.”

B. Perfect Infinitive (To Have + V3)

This places the infinitive action in the past, indicating that it happened before the main verb.

• “He seems to have forgotten the meeting.” (He forgot earlier; he seems that way now.)
• “I am lucky to have met you.”

C. Continuous Infinitive (To Be + V-ing)

Emphasises that the action of the infinitive is ongoing at the same time as the main verb.

• “He appears to be sleeping.”
• “She pretended to be reading when I entered.”

D. Perfect Continuous Infinitive (To Have Been + V-ing)

Combines perfect and continuous aspects — an ongoing action that was completed before the main verb.

• “He seems to have been working all day.” (He was working continuously; it seems that way now.)

7. Verbs That Change Meaning: Gerund vs. Infinitive

For a handful of verbs, the choice between a gerund and an infinitive completely changes the meaning. Here is a quick review focused on the infinitive side:

• Remember / Forget / Regret + Infinitive = a future action (a duty or obligation you must not forget to do).
  “Remember to lock the door.” (Don't forget your duty.)
  “I forgot to call her.” (I didn't do it.)
• Stop + Infinitive = pause one action in order to do another.
  “He stopped to smoke.” (He paused what he was doing to have a cigarette.)
• Try + Infinitive = make an effort (attempt something difficult).
  “I tried to lift the box, but it was too heavy.” (I made an effort.)
• Go on + Infinitive = proceed to a new action (change to a different task).
  “After introducing himself, he went on to explain the rules.”

8. Common Mistakes and How to Avoid Them

• Mistake: Using a gerund after a verb that requires an infinitive.
  Incorrect: “I want going home.”
  Correct: “I want to go home.”
• Mistake: Using a bare infinitive after certain verbs that require "to".
  Incorrect: “She asked him help her.”
  Correct: “She asked him to help her.”
• Mistake: Using an infinitive after a preposition (the only exception is when "to" is part of a phrasal verb like look forward to, which takes a gerund).
  Incorrect: “He is interested in to learn French.”
  Correct: “He is interested in learning French.”
• Mistake: Forgetting the "to" after "like" in certain structures.
  Incorrect: “I would like go now.”
  Correct: “I would like to go now.”

Summary Table: Infinitive Functions at a Glance