5 Uses of Infinitives

By Mark Nichol

An infinitive is a phrase, consisting of the word to and the basic form of a verb, that functions as a noun, an adjective, or an adverb. Here’s a discussion of the five types of infinitives.

1. Subject
An infinitive can constitute the subject of a sentence. For example, in “To go, even after all that trouble, didn’t seem worthwhile anymore,” “to go” is the action that drives the sentence.

2. Direct Object
In the sentence “We all want to see,” “to see” is the direct object, the noun (or noun substitute) that receives the action of the verb. “To see” refers to a thing being done — or, in this case, desired to be done: the act of seeing.

3. Subject Complement
In “My goal is to write,” “to write” is the subject complement. A subject complement looks just like a direct object, but the difference is in the type of verb preceding it. The verb in the previous example, want, is a transitive verb. (Transitive verbs have two defining characteristics: They precede a direct object, and they express an action.)

In “My goal is to write,” the verb is a copular, or linking, verb — one that links a subject to a word or phrase that complements it. (In this sentence, “to write” is the goal, so it’s the complement of goal. Note that in the previous example, “to see” is what those referred to as we want, but it’s not the complement of we.)

4. Adjective
In “She didn’t have permission to go,” “to go” modifies permission — it describes what type of permission is being discussed — so the phrase serves as an adjective.

5. Adverb
In “He took the psychology class to try to understand human behavior,” “to understand (human behavior)” explains why the taking of the class occurred, so it’s an adverb modifying the verb took.

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8 Responses to “5 Uses of Infinitives”

  • Matt Gaffney

    I agree with all the examples except the last. I can accept “to understand human behavior” as an adverbial phrase modifying “took,” but I don’t agree that “to understand,” on its own in the context, functions as an adverb.

  • Danny

    In the final example, you also have the infinitive “to try.” How is this infinitive functioning?

  • Nancy

    Seems to me that “to try” is the adverb and “to understand” is the direct object of “to try.” If I were editing this sentence, I would delete “to try” altogether.

  • Raymond

    I have the same question as Danny. In what was is “to try” used?

  • thebluebird11

    Wow…this is way too complicated. I feel cheated and want to know why I never learned this stuff. I had a private-school education for 18 years, and actually beyond…private college too, but I guess they don’t teach the fine points of grammar to bio majors. Wonderful thing that I can speak good English without actually knowing what I’m doing LOL

  • Warsaw Will

    I would call No 4 a Noun complement, not an adjective. Another example would be ‘His will to succeed was evident for all to see.’

    @Danny – in TEFL we call this an infinitive of purpose, meaning ‘in order to’.

    In my opinion, the fact that in these two examples infinitives can be said to function as adjectives and adverbs doesn’t make them themselves adverbs and adjectives, which are word classes (parts of speech). A relative clause functions adjectivally, but it isn’t an adjective (although in some grammars it’s called an adjective clause). In ‘the car door’, the noun ‘car’ is functioning adjectivally, but that doesn’t make it an adjective: it’s still a noun.

    Other functions for infinitives:

    6. Appositive – ‘His one ambition, to become a film star, became an obsession’

    7. Prepositional object – ‘Nothing remains except to say Goodbye.’

    8. Adjective complement – ‘He is certain to play for PSG one day’

  • Phil Brandt

    being a teacher of a handful of students in classical languages and many more who are biology majors with a limited grasp of the language, i empathize with thebluebird11. However, it is never too late to learn – pick up Latin or Greek or just about any rigorously declined/conjugated language and see your mastery of English blossom.

    regarding item #2 in the original post – i would actually call these complementary infinitives – certain verbs, include the verb “to want” but also verbs of ability, wish/desire, appearance, and others are regularly “completed” by a verb in the infinitive.

    while item #5 can be understood adverbially, i would think it would be better labeled a result or purpose clause, but that could be my classical languages coming to the fore. In Greek it is regularly indicated with a particle plus the subjunctive mood.

  • Frank W. Kresen

    Phil Brandt’s Comment:

    It may seem counter-intuitive, but Phil is right.

    If all the terminology used to discuss English grammar is unfamiliar to you and difficult, studying Latin or Greek — or any of the Romance Languages — will force you to learn and use these terms. The transfer and application of them to your understanding and correct use of English grammar will follow naturally.

    In my college years, I was in a pre-ministerial program, and Latin, Greek, Hebrew, and German were required (four years of each). Those studies enriched my understanding and appreciation of English to a degree that I appreciate anew again every day of my life.

    Later, just as I was setting up my freelance proofreading and copy-editing business, I worked as the language columnist for a magazine aimed at the secretarial/administrative assistant profession, and I recommended the same tactic as Phil is advocating here.

    If you’re a certain kind of person, it will change your life.

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