noun, adjective, and adverb
AdVerb
To help you
It is certainly unusual for an infinitive verb to be used as the predicate of a sentence, but in English all sorts of improbable constructions do come up. There is a line in Shakespeare that comes to mind: "To sleep, perchance to dream." As a grammarian I might try to expand the sentence by putting in the parts that are only implied: I am going to sleep and perchance I am also going to dream. In the expanded version, the predicate is going, which is not an infinitive. Even so, as originally written the line consists pretty much only of infinitive verbs.
Replace the present tense form of the verb by the verb phrase "will [or shall] + [infinitive form of the verb]".
An infinitive phrase. An infinitive phrase is a noun phrase with an infinitive as its head. Unlike the other noun phrases, however, an infinitive phrase can also function as an adjective or an adverb.
"To run" is an infinitive because it is the base form of the verb without any tense or subject attached to it. Infinitives are commonly used after certain verbs or as subjects, complements, or objects in a sentence.
The infinitive phrase here is "to watch".
An infinitive phrase will start with the base form of a verb (e.g., to eat, to run) and function as a noun, adjective, or adverb. A prepositional phrase will begin with a preposition (e.g., in, on, at) followed by a noun or pronoun, and it functions as an adjective or adverb to describe a noun or verb.
"To join the circus" is the infinitive phrase.
"To join the circus" is the infinitive phrase.
"To join the circus" is the infinitive phrase.
The infinitive phrase is "to join the circus" (an adverbial phrase).
An infinitive phrase will begin with an infinitive [to + simple form of the verb]. It will include objects and/or modifiers.
Infinitive
"to finish your test" is the infinitive phrase.
The infinitive phrase plays the role of an adverb in this sentence. It tells why you met at the park. In the sentence "You met at the park to run", "to run" is the infinitive phrase.