Verbs which have the past or the present form are called FINITE verbs. Verbs in any other form (infinitive, -ing, or -ed) are called NONFINITE verbs. This means that verbs with tense are finite, and verbs without tense are nonfinite. The distinction between finite and nonfinite verbs is a very important one in grammar, since it affects how verbs behave in sentences.
A nonfinite verb is any of several verb forms that are not finite verbs; that is, they cannot serve as the root of an independent clause. Nonfinite verbs found in English typically are infinitives, participles and gerunds. (They sometimes are called verbals—although that term has traditionally applied only to participles and gerunds.) Additional nonfinite forms found in some other languages include converbs, gerundives and supines.
Nonfinite verbs typically are not inflected by grammatical tense; and they present little inflection for other grammatical categories as well. Generally, they also lack a subject dependent. One or more nonfinite verbs may be associated with a finite verb in a finite clause, composing the elements of a verb catena, or verb chain.
Because English to a large extent lacks inflectional morphology, the finite and nonfinite forms of a verb may appear the same in a given context. In such a case, the environment surrounding the verb must be examined to determine whether it is finite or nonfinite.
English has three kinds of nonfinite verbs: infinitives, participles, and gerunds
Each of these nonfinite forms appears in a variety of environments.
A finite verb is a form of a verb that has a subject (expressed or implied) and can function as the root of an independent clause; an independent clause can, in turn, stand alone as a complete sentence. In many languages, finite verbs are the locus of grammatical information of gender, person, number, tense, aspect, mood, and/or voice. In elementary level, finite verb is the verb in a sentence which determines the tense. Finite verbs are distinguished from non-finite verbs, such as infinitives, participles, etc., which generally mark these grammatical categories to a lesser degree or not at all, and which appear below the finite verb in the hierarchy of syntactic structure.
In many languages (including English), there can be just one finite verb at the root of each clause (unless the finite verbs are coordinated), whereas the number of non-finite verbs can reach up to five or six, or even more, e.g.
He was believed to have been told to have himself examined.
Finite verbs can appear in dependent clauses as well as independent ones:
John said that he enjoyed reading.
Most types of verbs can appear in finite or non-finite form (and sometimes these forms may be identical): for example, the English verb go has the finite forms go, goes, and went, and the non-finite forms go, going and gone. The English modal verbs (can, could, will, etc.) are defective and lack non-finite forms.
A finite verb is generally expected to have a subject, as it does in all the examples above, although null-subject languages allow the subject to be omitted. For example, in the Latin sentence cogito ergo sum ("I think therefore I am") the finite verbs cogito and sum appear without an explicit subject – the subject is understood to be the first-person personal pronoun, and this information is marked by the way the verbs are inflected. In English, finite verbs lacking subjects are normal in imperative sentences: Come over here! Don't look at him!
English is an analytic language (old English is frequently presented as a synthetic language), which means it has limited ability to express these categories by verb inflection, and often conveys such information periphrastically, using auxiliary verbs. In a sentence such as
Sam laughs a lot. the verb form agrees in person (3rd) and number (singular) with the subject, by means of the -s ending, and this form also indicates tense (present), aspect ("simple"), mood (indicative) and voice (active). However most combinations of these categories need to be expressed using auxiliaries:
Sam will have been examined by this afternoon.
Here the auxiliaries will, have and been express respectively future time, perfect aspect and passive voice. (See English verb forms.) Highly inflected languages like Latin and Russian, however, frequently express most or even all of these categories in one finite verb.
