Nonfinite verb

Non-finite verbs, are verb forms that do not show tense, person, or number. They include:
Nonfinite verbs are used in constructions where there's no need to express tense directly. They help in creating sentences like "I want to go," where "to go" is nonfinite.
In the English language, a non-finite verb cannot perform action as the main verb of an independent clause. Non-finite verb forms in some other languages include converbs, gerundives and supines. The categories of mood, tense, and or voice may be absent from non-finite verb forms in some languages.
Because English lacks most inflectional morphology, the finite and the non-finite forms of a verb may appear the same in a given context.
In the following sentences, the non-finite verbs are emphasized, while the finite verbs are underlined.
In the above sentences, been, examined and done are past participles, want, have, refuse, accept and get are infinitives, and coming, running and trying are present participles (for alternative terminology, see the sections below).
In languages like English that have little inflectional morphology, certain finite and non-finite forms of a given verb are often identical, e.g.
Despite the fact that the verbs in bold have the same outward appearance, the first in each pair is finite and the second is non-finite. To distinguish the finite and non-finite uses, one has to consider the environments in which they appear. Finite verbs in English usually appear as the leftmost verb in a verb catena. For details of verb inflection in English, see English verbs.
In English, a non-finite verb form may constitute:
Each of the non-finite forms appears in a variety of environments.
The infinitive form of a verb is considered the canonical form listed in dictionaries. English infinitives appear in verb catenae if they are introduced by an auxiliary verb or by a certain limited class of main verbs. They are also often introduced by a main verb followed by the particle to (as illustrated in the examples below). Further, infinitives introduced by to can function as noun phrases or even as modifiers of nouns. The following table illustrates such environments:
English participles can be divided along two lines: according to aspect (progressive vs. perfect/perfective) and voice (active vs. passive). The following table illustrates the distinctions:
Participles appear in a variety of environments. They can appear in periphrastic verb catenae, when they help form the main predicate of a clause, as is illustrated with the trees below. Also, they can appear essentially as an adjective modifying a noun. The form of a given perfect or passive participle is strongly influenced by the status of the verb at hand. The perfect and the passive participles of strong verbs in Germanic languages are irregular (e.g. driven) and must be learned for each verb. The perfect and passive participles of weak verbs, in contrast, are regular and are formed with the suffix -ed (e.g. fixed, supported, opened).
A gerund is a verb form that appears in positions that are usually reserved for nouns. In English, a gerund has the same form as a progressive active participle and so ends in -ing. Gerunds typically appear as subject or object noun phrases or even as the object of a preposition:
Often, distinguishing between a gerund and a progressive active participle is not easy in English, and there is no clear boundary between the two non-finite verb forms.
Auxiliary verbs typically occur as finite verbs, but they also can occur as a participle (e.g. been, being, got, gotten, or getting) or, in the case of have, in a non-finite context as the complement to a modal verb relating to a perfect tense, e.g.:
Some languages, including many Native American languages, form non-finite constructions by using nominalized verbs. Others do not have any non-finite verbs. Where most European and Asian languages use non-finite verbs, Native American languages tend to use ordinary verb forms.
The non-finite verb forms in Modern Greek are identical to the third person of the dependent (or aorist subjunctive) and it is also called the aorist infinitive. It is used with the auxiliary verb έχω (to have) to form the perfect, the pluperfect and the future perfect tenses.
For an overview of dependency grammar structure in modern linguistic analysis, three example sentences are shown. The first sentence, The proposal has been intensively examined, is described as follows.
The three verbs together form a chain, or verb catena (in purple), which functions as the predicate of the sentence. The finite verb has is inflected for person and number, tense, and mood: third person singular, present tense, indicative. The non-finite verbs been and examined are, except for tense, neutral across such categories and are not inflected otherwise. The subject, proposal, is a dependent of the finite verb has, which is the root (highest word) in the verb catena. The non-finite verbs lack a subject dependent.
The second sentence shows the following dependency structure:
The verb catena (in purple) contains four verbs (three of which are non-finite) and the particle to, which introduces the infinitive have. Again, the one finite verb, did, is the root of the entire verb catena and the subject, they, is a dependent of the finite verb.
The third sentence has the following dependency structure:
Here the verb catena contains three main verbs so there are three separate predicates in the verb catena.
The three examples show distinctions between finite and non-finite verbs and the roles of these distinctions in sentence structure. For example, non-finite verbs can be auxiliary verbs or main verbs and they appear as infinitives, participles, gerunds etc.