A non-finite verb (sometimes called a verbal) is any of several verb forms that are not finite verbs; that is, they cannot serve as the root of an independent clause. The non-finite verb forms found in English are infinitives, participles and gerunds; additional such forms found in some other languages include gerundives and supines. Non-finite verbs are typically not inflected for tense, and compared with finite verbs usually display less inflection for other grammatical categories as well. They also typically lack a subject dependent. A typical finite clause is based on a single finite verb, but it may in addition contain one or more non-finite verbs, building a verb catena with the finite verb.
Since English lacks inflectional morphology to a large extent, the finite and non-finite forms of a given verb are often identical. In such cases, one has to examine the environment in which the verb appears to know whether it is finite or non-finite.
The following sentences each contain one finite verb (underlined) and multiple non-finite verbs (bolded):
- The proposal 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.
In the above sentences, been, examined and done are past participles, want, have, refuse and accept are infinitives, and coming and running 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.
Types of non-finite verbs 
English has three kinds of non-finite verbs:
Each of these non-finite forms appears in a variety of environments.
The infinitive of a verb is considered the "base" form; it is the form that is listed in dictionaries. Infinitives in English appear in verb catenae where they are introduced by an auxiliary verb or by a certain limited class of main verbs. They are also often frequently introduced by a main verb followed by the particle to (as illustrated in the trees below). Further, infinitives introduced by to can function as noun phrases, or even as modifiers of nouns. The following table illustrates these environments:
Infinitive Introduced by a (modal) auxiliary verb Introduced by a main verb Introduced by a main verb plus to Functioning as noun phrase Functioning as the modifier of a noun laugh Do not laugh! That made me laugh. I tried not to laugh. To laugh would have been unwise. the reason to laugh leave They may leave. We let them leave. They refused to leave. To leave was not an option. the thing to leave behind expand You should expand the explanation. We had them expand the explanation. We hope to expand the explanation. To expand the explanation would have been folly. the effort to expand
Infinitive Progressive active participle Perfect active participle Passive participle fix The guy is fixing my bike. He has fixed my bike My bike was fixed. open the flower opening up The flower has opened up. The flower has been opened up. support the news supporting the point The news has supported the point. the point supported by the news drive She is 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, in which case they help form the main predicate of a clause (as illustrated with the trees above), or 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 passive participles of strong verbs in Germanic languages are irregular (e.g. driven); their form is idiosyncratic. The perfect and passive participles of weak verbs, in contrast, are regular; they 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 (see above), ending in -ing. Gerunds typically appear as subject or object noun phrases, or even as the object of a preposition:
Infinitive Gerund as subject Gerund as object Gerund as object of a preposition solve Solving problems is satisfying. I like solving problems. No one is better at solving problems. jog Jogging is boring. He has started jogging. Before jogging, she stretches. eat Eating too much made me sick. She avoids eating too much. That prevents you from eating too much. investigate Investigating 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; the line between the two non-finite verb forms is not clear.
Non-finite verbs in other languages 
Some languages, including many Native American languages, form non-finite constructions using nominalized verbs. Others do not have any non-finite verbs; where most European or Asian languages use non-finite verbs, they use ordinary verb forms.
Non-finite verb form in Modern Greek 
The Modern Greek non-finite verb form is 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, pluperfect and future perfect tenses.
Non-finite verbs in theories of syntax 
On a dependency grammar account of sentence structure, the first of the example sentences given earlier ("The proposal has been intensively examined today") receives the following analysis:
The three verbs together form a verb catena (in purple). This verb catena functions as the matrix predicate of the sentence. The finite verb has is inflected for person (3rd person), number (singular), tense (present), and mood (indicative). The non-finite verbs are not inflected in this sense; they are neutral with respect to these categories. The subject is a dependent of the finite verb, whereby the non-finite verbs lack a subject dependent. The finite verb is the root (highest word) in its verb catena. The second sentence has the following dependency structure:
The verb catena in this case (in purple) contains four verbs and the particle to. The particle to always introduces an infinitive. Three of the four verbs are non-finite verbs. The one finite verb is again necessarily the root of the entire verb catena. The subject is again dependent of the finite verb. The third sentence has the following dependency structure:
The verb catena in this sentence contains three main verbs, which means there are three separate predicates in this one verb catena (each of which can be negated). The three examples demonstrate the key distinction between finite and non-finite verbs and the role that the distinction plays in sentence structure. Non-finite verbs can be auxiliary verbs or main verbs and they appear as infinitives or participles or gerunds or etc.
- Concerning the lack of inflection for these grammatical categories, see for instance Radford (1997:508f.), Tallerman (1998:68), and Finch (2000:92f.).
- Concerning the fact that the left-most verb is the finite verb, see Tallerman (1998:65).
- Mithun, Marianne. 1999. The languages of native America. Cambridge: Cambridge University Press.
- Dodds, J. 2006. The ready reference handbook, 4th Edition. Pearson Education, Inc.. ISBN 0-321-33069-2
- Finch, G. 2000. Linguistic terms and concepts. New York: St. Martin's Press.
- Radford, A. 1997. Syntactic theory and the structure of English: A minimalist approach. Cambridge, UK: Cambridge University Press.
- Rozakis, L. 2003. The complete idiot's guide to grammar and style, 2nd Edition. Alpha. ISBN
- Tallerman, M. 1998. Understanding syntax. London: Arnold.
See also 
- Grammatical conjugation
- Lexical category
- Verb phrase
- Verbal noun
- Balancing and deranking
- Owl Online Writing Lab: Verbals: Gerunds, Participles, and Infinitives