An infinitive is the most basic form of a verb. You’ll usually see it with the word to, as in to eat or to think. An infinitive phrase is an infinitive plus complements and modifiers. To eat vegetables daily and to think about a solution are infinitive phrases. While infinitives themselves are verbs, infinitive phrases can be used as nouns, adjectives, or adverbs.
Adverbial infinitive phrases can modify verbs, adjectives, or adverbs. For example: “Lily was ready to go to the movies.” You could just say “Lily was ready,” and it would make perfect sense. But what was she ready for? That’s where the infinitive phrase, to go to the movies, comes in. It modifies the main adjective ready, providing more detail.
You might also see an adverbial infinitive at the beginning of a sentence, as in “To make a long story short, we decided to go to the party.”
The word nominal means something can act as a noun in a sentence. Nominal infinitive phrases can be the subject of a sentence, the direct object, or the object of a preposition. For example, “To visit Italy had been her dream for years.” Here, the infinitive phrase to visit Italy functions as a noun, and is the subject of the sentence.
An adjectival infinitive phrase modifies a noun or pronoun. In other words, it acts like an adjective. For example: “As long as she’s here, I’ll always have a friend to talk to me.” The infinitive phrase to talk to me modifies (or describes) the noun friend.
You can form the passive voice by combining an infinitive with be and a participle. For example: “The clothes need to be washed.” The passive voice describes something happening to a noun (a person place or thing), rather than the noun itself doing something.
Infinitives also appear in perfect tenses, where they’re used with have and a participle. For example: “I would’ve liked to have left the park much earlier.” To have left is a present perfect infinitive.
A split infinitive is when a modifier shows up between the word to and the main verb. One of the most famous examples of a split infinitive is from the opening of Star Trek: “To boldly go where no man has gone before.” Here, the infinitive is to go. The word boldly appears in the middle of it, “splitting” it.
Not everyone okay with split infinitives. So in formal writing, it’s best to avoid them. Some grammarians do agree that split infinitives are acceptable under certain circumstances. They suggest that the modifier should appear where it makes the most sense or has the strongest impact.
While the word to is the general marker of an infinitive, it’s sometimes omitted. For example, “Rip Van Winkle did nothing but fish all day without a murmur.” This sentence is understandable without the word to before the verb fish. Infinitives without to are called bare infinitives.
Not every phrase that begins with to is an infinitive phrase. The word to is a preposition, and can also begin prepositional phrases. For example, “He sent a letter to his parents.” Here, to begins a prepositional phrase, not an infinitive phrase.
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