# Nonfinite verb

Non-finite verbs, are verb forms that do not show tense, person, or number. They include:
* Infinitives (e.g., to go, to see) - They often function as nouns or the base form of a verb
* Gerunds (e.g., going, seeing) - These act as nouns but are derived from verbs
* Participles (e.g., gone, seen) - These can function as adjectives or part of verb tenses (like has gone)
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.

## Examples

In the following sentences, the non-finite verbs are emphasized, while the finite verbs are underlined.
       Verbs appear in almost all sentences.
       This sentence is illustrating finite and non-finite verbs.
       The dog will have to be trained well.
       Tom promised to try to do the work.
       The case has been intensively examined today.
       What did they want to have done about that?
       Someone tried to refuse to accept the offer.
       Coming downstairs, she saw the man running away.
       I am trying to get the tickets.
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.
       a. They laugh a lot. - Finite verb (present tense) in bold
       b. They will laugh a lot. - Non-finite infinitive in bold
       a. Tom tried to help. - Finite verb (past tense) in bold
       b. Tom has tried to help. - Non-finite participle in bold
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.

## Categories
### English

In English, a non-finite verb form may constitute:
* an infinitive verb, including the auxiliary verb have —
   * within a verb phrase that is predicated by a modal verb (e.g., "I could have cried").
   * within a to-infinitive phrase (e.g., "They seem to have moved").
* a participle.
* a gerund.
Each of the non-finite forms appears in a variety of environments.

#### Infinitive

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:
          InfinitiveIntroduced via auxiliary verbIntroduced via causative verbIntroduced via finite verb plus toFunctioning as noun phraseFunctioning as an adjective laughDo not laugh!That made me laugh.I tried not to laugh.To laugh would have been unwise.the reason to laugh leaveThey may leave.We let them leave.They refused to leave.To leave was not an option.the thing to leave behind expandYou should expand the explanation.We had them expand the explanation.We hope to expand the explanation.Our goal is to expand.the effort to expand

#### Participle

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:
          ParticipleProgressive active participleProgressive passive participlePerfect active participlePerfect passive participle fixThe guy is fixing my bike.I saw the guy fixing my bike.He has fixed my bike.My bike was fixed. openThe flower was opening up.I saw the flower opening up.The flower has opened up.The flower has been opened up. supportThe news is supporting the point.She watched the news supporting the point.The news has supported the point.I understood the point supported by the news driveShe is driving our car.I watched her driving our car.She has driven our car.Our car should be driven often.
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).

#### Gerund

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:
          GerundGerund as subjectGerund as objectGerund as object of a preposition solveSolving problems is satisfying.I like solving problems.No one is better at solving problems. jogJogging is boring.He has started jogging.Before jogging, she stretches. eatEating too much made me sick.She avoids eating too much.That prevents you from eating too much. investigateInvestigating the facts won't hurt.We tried investigating the facts.After investigating the facts, we made a decision.
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 verb

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.:
          Modal verb + havestative participlePerfect active participlePerfect passive participle could haveThe guest could have been a bore.The guest could have been boring us .The guest could have been bored. might haveThe dog might have been a surprise.The dog might have been surprising everyone .The dog might have been surprised. should haveOur bid should have been a win.Our bid should have been winning support.Our bid should have been won . would haveTheir troops would have been a loss.Their troops would have been losing ground.Their troops would have been lost.

### Native American languages

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.

### Modern Greek

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.

## Theories of syntax

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.