What Is an Infinitive?

Infinitives are an important part of grammar. Whether you’re studying for a grammar test in school or a writer looking to learn more about what infinitives are (and their potential capitalization implications), you’ve come to the write place.

What Is an Infinitive: A Description of Infinitives

An infinitive is a form of the word that usually follows another verb, participle (a verb form ending in -ing), or noun. It is generally used as an adjective and as part of gerunds (parts of verbs that look like gerunds but act as adjectives). Infinitives are also used with modal verbs. There are several kinds of infinitives: simple, continuous, perfect, passive, plus some others you might come across if you study grammar and literature very hard.

Infinitives can be difficult to master because there are so many different kinds. The most common kind uses the words “to” and “be” instead of helping (“helping”) words like “will,” “shall,” and “when.” It’s called the to-infinitive.

Overall, an infinitive has a subject and follows the verb “to” plus whatever other verb form (like a participle) or noun it is describing. Here’s an example that uses a gerund:
To see is to believe.
Here, “to see” describes seeing. We can also say that seeing is described by the infinitive “to see”. Notice how easy it was for us to turn this sentence into a question – all we had to do was put in the helping word “that”:
Is it true that to see is to believe?

Infinitive-To-Verb Agreement

Infinitives are just as important as verbs. They’re used with main verbs which they describe. Because of this, you must make them agree (your infinitive’s subject must be the same as the main verb it follows). These are two examples of correct agreement:
  1. To see is better than to hear. – The infinitive sees is describing the verb see; these infinitives match up. Seeing is also correct because the infinitive and its helping verbs match each other.
  2. Telling your friend a secret might make you feel ashamed if she didn’t keep it. – This sentence has three verbs in it, but even though there are lots of them, all three are telling us that someone told something to someone else (we’ll talk about modal verbs like “might” later on in this lesson); what they’re actually doing is telling about the situation that led up to the person feeling ashamed. The infinitives in this sentence match their respective verbs: told, make, and felt.

What Does Infinitive Mean: Infinitives and Direct Objects

Some infinitives have direct objects (subjects of a verb); let’s talk about how those work. Remember when we said that infinitives are always adjectival? That means they can be used as a complement, too (the thing being described by an adjective or complement is called its “complement”).
For example:
That car is what I want to buy.
In this sentence, the car is doing what describes wanting — buying it; you could say that buying it is something that I want to do.
The dog wants me to throw something for it to fetch.
In this sentence, the dog (the subject) is doing what describes wanting; it wants me to do something. The thing that I have to do is shown by the direct object of the infinitive—throw and fetch.

It might be hard to tell whether or not an infinitive has a direct object sometimes, but there are certain clues:

When an adjective modifies a noun right before the infinitive, you can assume that when the noun leaves, its modifier will go with it. This means that if there’s an adjective describing a noun right before an infinitive, then we can say with confidence that the infinitival subject and verb must be in agreement:

I hope to see a blue sky this afternoon.
The adjective “blue” describes the noun “sky”; the infinitive complement is in agreement with its verb, too, so we can safely call it an infinitive. (This sentence has another example of infinitival-to-verb agreement; later on, we’ll talk about how easy and important that kind of agreement is.)
My friend told me to buy a new car.
In this sentence, the noun “car” doesn’t have any adjectives or anything else modifying it after I bought a. Since its direct object (what I’m going to buy) isn’t modified by anything else either, we know for sure it’s an infinitive. (In this sentence, it’s also correct to say that I am going to buy is a direct object; the infinitive and helping verbs, in this case, are still in agreement with each other.)

The first word after an infinitive often forces you into saying that there’s a direct object. Consider these two examples:

I want you to drive me home.
The second word of the second option is “me”; since it follows an infinitive, it must be a direct object. You could easily rewrite this sentence as Your driving me home would make me very happy, but if you wanted to keep the same meaning, then you’d have to use another helping verb (like allow ): To allow me to drive home would make me very happy. (In this sentence, “to allow me” can be considered a noun).

As you’ve probably guessed by now, infinitives come in all shapes and sizes. They’re flexible; they usually take on the verbal characteristics of whatever verb is immediately before them, but they can also show characteristics that don’t match up with their other verbs entirely.

Infinitives as Adjectives

Let’s say we want to describe the noun “gender” as being feminine; then this is what we’d do:
The gender of the president and her advisors was a factor in the vote.
In this sentence, the infinitive “to be a factor” modifies the noun “gender;” however, it doesn’t mean that it’s just describing gender without actually doing anything—no adjectives can do that! Instead, it must have some kind of verbal characteristics, so we could call it an infinitival adjective.

Because an infinitival adjective always describes whatever comes right before it (like other adjectives could), you can see why they’re often called “adjective prepositions.”

Infinitives as Adverbs

What if we want to make an infinitive adverb? In most cases, you turn it into a present participle:
The president can only be impeached by the house of representatives.
Here, the infinitival verb “to be impeachable” is describing the noun “president.” It’s making her reprehensible, so that makes it an adverb. You might think this means “by members of the house,” but infinitives are flexible: because impeachment can only happen while she’s in office (and being impeachable is like attending college), this infinitive describes what happens after the verb vote (“was voted out”).

What Is a Split Infinitive?

If you’ve ever seen a sentence like “to boldly go,” then, in that case, you were looking at a split infinitive. There is no need to wonder about what is a split infinitive, this term refers to the habit some people have who want to place an adverb between the noun and verb of an infinitive; however, as we saw above, this often results in weird word order.
Consider these two examples:
  1. The committee decided not to approve the sale.
  2. The committee decided to not approve the sale.

In both cases, it looks like there are two verbs instead of one! In English grammar, this is called a split infinitive because you’re viewing two parts of speech (the verb and the adjective) that should really be together on their own.

Before we talk about how to avoid split infinitives, let’s first consider our options:

“The committee decided not to approve the sale.”

In this option, they’re a single unit—there’s no place to stick an adverb in between them! This is why it makes sense that many linguists recommend that you avoid split infinitives: if you keep your sentences short and sweet, then there are fewer opportunities for mistakes.

You might be thinking, “I see what you did there,” but just because it’s acceptable doesn’t mean that we have to like it.

After all, who hasn’t heard someone do something like “My dog likes playing fetch with me very much?” We could say “My dog likes to play fetch with me very much?” Both sentences work, but the former usually rolls off the tongue easier. (Note: This sentence does have a split infinitive, but we could also rearrange it to avoid it. For example: “My dog likes playing fetch, and he really enjoys playing with me.”)

Are Infinitives Capitalized in Titles?

You should only capitalize the infinitive word “to” in AP style. All other styles lowercase the infinitive word “to”.

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Capitalize My Title is a dynamic title capitalization tool used to make sure your titles or headlines use proper capitalization rules according to various style guides include APA, AP, MLA, and Chicago. It also counts your words and checks for grammar issues.


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