An infinitive is the basic form of a verb, often with “to,” that can act like a noun, adjective, or adverb in a sentence.

Simple meaning

  • In English, the infinitive is usually “to” + verb: to eat, to go, to read.
  • It does not show tense (no past, present, or future by itself).
  • It can also appear without “to” in some patterns (called a bare infinitive): “Help me carry this,” “I saw him leave.”

Quick examples

  • To learn is fun. (Infinitive = “to learn,” used as a noun, the subject.)
  • I want to sleep. (Infinitive = “to sleep,” used as a noun, the object of “want.”)
  • I need a book to read. (“To read” describes “book,” so it works like an adjective.)
  • She left early to study. (“To study” explains why she left; it works like an adverb.)

Mini sections

1. Form: how infinitives look

Most common forms:

  • Full (to‑infinitive): to be, to run, to sing.
  • Bare infinitive (without “to”): be, run, sing when used after certain verbs or modals, like can, must, make, let, see, hear.

Examples:

  • You must go now. (“Go” is a bare infinitive after “must.”)
  • They saw her leave. (“Leave” is bare infinitive after “saw her.”)

2. Function: what infinitives do

Infinitives are verbs in form, but they often function as:

  • Nouns: “To help others is important.”
  • Adjectives: “I have a project to finish.”
  • Adverbs: “He came to apologize.”

They are “non‑finite” verbs, meaning they don’t show who does the action or when; they just name the action in a general, abstract way.

3. A tiny “story” to remember it

Think of the infinitive as the “free” version of a verb, before it’s tied to time or a subject. Hamlet’s line “To be or not to be?” uses the verb be in its infinitive form, talking about existence in general, not about who exists or when.

Once you change “to be” into “was” or “is,” it’s no longer infinitive because it now shows tense and a specific subject.

Common extra point: split infinitives

Sometimes another word goes between “to” and the verb, like:

  • “to quickly eat” instead of “to eat quickly.”

This is called a split infinitive. Some style guides dislike it, but many modern writers accept it, especially in informal English.

Bottom line:
An infinitive is the base form of a verb (with or without “to”) used not to show time, but to name an action or idea, often working like a noun, adjective, or adverb.

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