Ok, let’s face the facts: English is a tough and often weird language. English grammar is rarely cut and dry. We all know it, so why mention this now? Well, we’re about to talk about infinitives. Are they verbs? Are they nouns? Are they adjectives? Are they adverbs? Are they taking all of our missing socks? The answer to the last question is “No” (probably), but the other questions are trickier to answer. Many parts of speech don’t like staying in their own little area and will sometimes cross over into other categories. Infinitives are a perfect example of English complexity, so let’s try as best we can to nail down these tricky words—after we double check our sock drawer.
What is an infinitive?
Things are going to get a little complicated so let’s start simply. An infinitive is a verb form that can be found in many languages, and each of them uses infinitives differently. For example, if you have ever studied Spanish, you know that words like hablar (“to speak”), gustar (“to like”), and leer (“to read”) are infinitives. In English, an infinitive is identical to the simple or basic form of the verb you will find if you look one up in our dictionary. Eat, sleep, play, and go are examples of infinitives. As you might know, the first person singular present tense also typically resembles the base form of the verb, as in the sentence I sleep.
So, how do we actually use infinitives? Well, infinitives are not often used by themselves. In most sentences, an infinitive will follow a modal verb in a verb phrase as in can leave or must buy or it will follow a function word, almost always to, as in the famous “To be or not to be” from Shakespeare’s Hamlet. When an infinitive is used with a function word and other words, we refer to this as an infinitive phrase. This can be confusing, as many English speakers will also refer to infinitive phrases such as to run or to move as simply “infinitives.”
Infinitives are derived from verbs and can act as verbs when used with an auxiliary verb (helping verb) in a sentence. For example, the following sentences use infinitives with modal verbs:
- I can play three different instruments.
- You must give me the money you owe me.
- My sisters and I would watch cartoons every Saturday when we were kids.
Is this the only way we can use infinitives? Not by a long shot! Let’s look at the different types of infinitives to see how useful they can be.
Get some help learning more about auxiliary verbs in this closer look at them.
Types of infinitives
Infinitives and infinitive phrases come in several different types, and they all have their specific uses in sentences.
Nominal infinitives
In grammar, the word nominal means that something can function as a noun in a sentence. Like gerunds, infinitive phrases can function as a noun in a sentence or clause. This means that infinitive phrases can be subjects, direct objects, or objects of prepositions. For example:
- Subject: To play professional baseball is my son’s dream.
- Direct object: All of my friends want to go to the concert.
- Object of a preposition: We had no choice but to obey.
Adverbial infinitives
The word adverbial means that something can function as an adverb. Adverbs modify verbs, adjectives, and clauses. So, adverbial infinitive phrases can also be used to modify these things. For example:
- She agreed to negotiate. (Modifies the verb agreed)
- The movie was too quiet to hear. (Modifies the adjective quiet)
- To find change on the beach, you will need a metal detector. (Modifies the main clause)
Adjectival infinitives
As you might guess, the word adjectival means something can function as an adjective. Adjectives modify nouns and pronouns, so adjectival infinitive phrases are—you guessed it!—used to modify nouns and pronouns:
- When it comes to romance, Juan is the guy to ask. (To ask modifies the noun guy)
- It is for me to know and for you to find out. (To know modifies the pronoun me and to find out modifies the pronoun you)
Bare infinitives
Sometimes, the word to is omitted from an infinitive phrase. When it is, we refer to this as a bare infinitive. Often, bare infinitives make a sentence look less awkward than if the word to was present:
- Captain Hook made Peter Pan walk the plank.
- Our mean teacher let us sweat a little before reading the exam results.
- Everyone wanted to hear her sing songs from her new album.
Infinitives in the passive voice
It is possible to put infinitives in the passive voice. When we use the passive voice, the subject has something happen to it rather than perform an action itself. To use an infinitive in the passive voice, we use the verb be followed by a past participle of a verb. For example:
- There is work to be done.
- The fish need to be fed and the cats have to be let out.
Infinitives in the present perfect tense
It is possible to use an infinitive phrase in the present perfect tense. To do so, we use the verb have with the past participle of a verb:
- It would have been nice to have talked to Ashley before she left for college.
- Based on the fossil record, it would’ve been impossible for cavemen to have ridden dinosaurs.
Dip into all the present tenses, including the present perfect, with this article.
What are split infinitives? Rules and best practices
Although it may frustrate your English teacher, it is possible to split up an infinitive with the word to in an infinitive phrase in order to put a modifier in between. We refer to these split infinitives as … split infinitives. A famous example of this is found in the opening of Star Trek, which states the crew has a mission “to boldly go where no man has gone before.” In most cases, the modifier that splits the infinitive is an adverb. Because many sentences would sound awkward if the adverb followed the entire infinitive phrase, we often split an infinitive to make a more natural sounding sentence. You can see this in the following two sentences:
- Henry tried and failed to walk his big clumsy dog Rufus slowly down the street.
- Henry tried and failed to slowly walk his big clumsy dog Rufus down the street.
Both of these sentences are grammatically correct and have the same meaning, but the second sentence splits the infinitive to move the adverb toward the beginning of the sentence. As a result, the second sentence is a little easier to read and understand.
You can learn more about split infinitives in our more detailed exploration of them.
Infinitives vs. prepositional phrases
In many sentences, an infinitive is accompanied by the word to. If you see the word to followed by the base form of a verb, you are almost always dealing with an infinitive phrase.
However, not every phrase that begins with to is an infinitive phrase. To is also a commonly used preposition, which means it can also be used to begin prepositional phrases. When used in a prepositional phrase, to is followed by a noun, pronoun, noun phrase, a word acting as a noun, and any other modifiers. You’ll notice that a preposition phrase doesn’t include a verb or word acting as a verb, which is the key to differentiating it from an infinitive phrase. The following sentences show this difference between infinitive phrases and prepositional phrases:
- Infinitive phrase: It is time to eat lunch. (To is followed by an infinitive, not a noun)
- Prepositional phrase: Bring my lunch to me. (To is followed by a pronoun)
However, there are two things you should watch out for:
1. When used as a preposition, to can be followed by a gerund. A gerund looks like a verb, but it is used as a noun. Gerunds also always end in -ing, which infinitives never do.
- They resorted to burning furniture for warmth. (Burning is a gerund that begins a gerund phrase)
2. It is possible for long prepositional phrases to have infinitive phrases within them.
- She gave the letter to the man who knew how to dance the fandango.
In the sentence above, the verb gave is modified by a long prepositional phrase that begins with to the man and has an infinitive phrase within it. Remember, infinitive phrases can modify nouns, adjectives, and adverbs. But wait, there’s more! A noun within an infinitive phrase can also be modified by a prepositional phrase, too. This can possibly lead to extraordinary long (and silly) sentences involving many subordinate prepositional phrases that modify nouns within infinitive phrases:
- I brought the package to the woman who asked to use the bathroom to the left of the table of the chef that learned to make desserts by watching fancy cooks who went to French culinary schools to learn their trade.
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