An infinitive is the unmarked base form of the verb, that which is used after a modal auxiliary and is the form of the verb listed in a dictionary entry. An infinitive phrase is an infinitive verb (usually) preceded by the infinitive marker TO (which is the KEY MARKER) and can include the subject or the complements (or both) of the verb from which it is derived.

You should be able to locate an infinitive phrase. The marker for an infinitive phrase is:

to + verb (in its base form)

An infinitive phrase can function as nominal, adjectival, or adverbial:

To wait seemed foolish when decisive action was required. (subject)

Everyone wanted to go. (direct object)

His ambition is to fly. (subject complement)

He lacked the strength to resist. (adjectival)

We must study to learn. (adverbial)

You should be able to identify all infinitive phrases you see in a sentence:

People were amused to watch the monkeys climbing in the trees.

to watch the monkeys

You should be able to identify the function of an infinitive phrase:

He even found a place on the board to put his flyer.

To put his flyer = Adjectival infinitive, modifying place

As with prepositional phrases, identifying the function of non-finite verb phrases begins with proximity: who is the phrase hanging out with? A non-finite verb phrase will be nominal if it fills a noun role (subject, direct object, object of the preposition). A non-finite verb phrase will most often be adjectival if it follows immediately after a noun. And a non-finite verb phrase will most often be adverbial if it provides extra information about time or place, but the key tests for determining if non-finite verb phrases are adverbial are always movement and deletion.

You should be able to combine sentences to create your own infinitive phrases:

I expect SOMETHING.  The hybrid car will use less gasoline.

I expect the hybrid car to use less gasoline.

NOTE: While it is not a common practice, keep in mind that an infinitive phrase does not require the infinitive marker TO, so you might suspect an infinitive without the marker if a base verb does not have a subject and it is functioning as a modifier. Again, the key is to recognize a verb in its base form, then determining if it has a subject and is serving as the action of that subject. If not, suspect an infinitive phrase with a deleted TO.

Finally, you should be able to distinguish between the preposition TO and the infinitive marker TO. If you are still having trouble, review the discussion in the prepositional phrase page.

To test your understanding of the concepts discussed on this page, begin with the link below for an example practice exercise:

INFINITIVE PHRASE SAMPLE EXERCISE

For a bit more of a challenge, analyze the following sentence from The Wonderful Wizard of Oz for infinitive phrases.

When Dorothy was standing in the doorway, she could see nothing but the great gray prairie on every side. The sun had baked the plowed land into a gray mass, with little cracks running through it. Even the grass was not green, for the sun has been burning the tops of the long blades for decades, until they were the same gray color to be seen everywhere.

To review your answers to these two samples, check the INFINITIVE PHRASE SAMPLES ANALYSES page.