Verb

A verb, from the Latin verbum meaning word, is a word (part of speech) that in syntax conveys an action (bring, read, walk, run, learn), or a state of being (be, exist, stand). In the usual description of English, the basic form, with or without the particle to, is the infinitive. In many languages, verbs are inflected (modified in form) to encode tense, aspect, mood and voice. A verb may also agree with the person, gender, and/or number of some of its arguments, such as its subject, or object.

Agreement
In languages where the verb is inflected, it often agrees with its primary argument (the subject) in person, number and/or gender. With the exception of the verb to be, English shows distinctive agreement only in the third person singular, present tense form of verbs, which is marked by adding "-s" (I walk, he walks) or "-es" (he fishes). The rest of the persons are not distinguished in the verb (I walk, you walk, they walk, etc.).

Latin and the Romance languages inflect verbs for tense–aspect–mood and they agree in person and number (but not in gender, as for example in Polish) with the subject. Japanese, like many languages with SOV word order, inflects verbs for tense/mood/aspect as well as other categories such as negation, but shows absolutely no agreement with the subject - it is a strictly dependent-marking language. On the other hand, Basque, Georgian, and some other languages, have polypersonal agreement: the verb agrees with the subject, the direct object and even the secondary object if present, a greater degree of head-marking than is found in most European languages.

Valency
The number of arguments that a verb takes is called its valency or valence. Verbs can be classified according to their valency: Weather verbs are often impersonal (subjectless, or avalent) in null-subject languages like Spanish, where the verb llueve means "It rains". In English, they require a dummy pronoun, and therefore formally have a valency of 1.
 * Avalent (valency = 0): the verb has neither a subject nor an object. Zero valency does not occur in English; in some languages such as Mandarin Chinese, weather verbs like snow(s) take no subject or object.
 * Intransitive (valency = 1, monovalent): the verb only has a subject. For example: "he runs", "it falls".
 * Transitive (valency = 2, divalent): the verb has a subject and a direct object. For example: "she eats fish", "we hunt nothing".
 * Ditransitive (valency = 3, trivalent): the verb has a subject, a direct object, and an indirect object. For example: "He gives her a flower."

Intransitive and transitive verbs are the most common, but the impersonal and objective verbs are somewhat different from the norm. In the objective the verb takes an object but no subject; the nonreferent subject in some uses may be marked in the verb by an incorporated dummy pronoun similar to that used with the English weather verbs. Impersonal verbs in null subject languages take neither subject nor object, as is true of other verbs, but again the verb may show incorporated dummy pronouns despite the lack of subject and object phrases. Tlingit lacks a ditransitive, so the indirect object is described by a separate, extraposed clause.

English verbs are often flexible with regard to valency. A transitive verb can often drop its object and become intransitive; or an intransitive verb can take an object and become transitive. For example, the verb move has no grammatical object in he moves (though in this case, the subject itself may be an implied object, also expressible explicitly as in he moves himself); but in he moves the car, the subject and object are distinct and the verb has a different valency.

In many languages other than English, such valency changes are not possible; the verb must instead be inflected in order to change the valency.

Tense, aspect, and modality


Depending on the language, verbs may express grammatical tense, aspect, or modality. Grammatical tense is the use of auxiliary verbs or inflections to convey whether the action or state is before, simultaneous with, or after some reference point. The reference point could be the time of utterance, in which case the verb expresses absolute tense, or it could be a past, present, or future time of reference previously established in the sentence, in which case the verb expresses relative tense.

Aspect expresses how the action or state occurs through time. Important examples include:
 * perfective aspect, in which the action is viewed in its entirety though completion (as in "I saw the car")
 * imperfective aspect, in which the action is viewed as ongoing; in some languages a verb could express imperfective aspect more narrowly as:
 * habitual aspect, in which the action occurs repeatedly (as in "I used to go there every day"), or
 * continuous aspect, in which the action occurs without pause; continuous aspect can be further subdivided into
 * stative aspect, in which the situation is a fixed, unevolving state (as in "I know French"), and
 * progressive aspect, in which the situation continuously evolves (as in "I am running")
 * perfect, which combines elements of both aspect and tense, and in which both a prior event and the state resulting from it are expressed (as in "I have studied well")

Aspect can either be lexical, in which case the aspect is embedded in the verb's meaning (as in "the sun shines", where "shines" is lexically stative); or it can be grammatically expressed, as in "I am running".

Modality expresses the speaker's attitude toward the action or state given by the verb, especially with regard to degree of necessity, obligation, or permission ("You must go", "You should go", "You may go"), determination or willingness ("I will do this no matter what"), degree of probability ("It must be raining by now", "It may be raining", "It might be raining"), or ability ("I can speak French"). All languages can express modality with adverbs, but some also use verbal forms as in the given examples. If the verbal expression of modality involves the use of an auxiliary verb, that auxiliary is called a modal verb. If the verbal expression of modality involves inflection, we have the special case of mood; moods include the indicative (as in "I am there"), the subjunctive (as in "I wish I were there"), and the imperative ("Be there!").

Voice
The voice of a verb expresses whether the subject of the verb is performing the action of the verb or whether the action is being performed on the subject. The two most common voices are the active voice (as in "I saw the car") and the passive voice (as in "The car was seen by me" or simply "The car was seen").

Most languages have a number of verbal nouns that describe the action of the verb.

In the Indo-European languages, verbal adjectives are generally called participles. English has an active participle, also called a present participle; and a passive participle, also called a past participle. The active participle of break is breaking, and the passive participle is broken. Other languages have attributive verb forms with tense and aspect. This is especially common among verb-final languages, where attributive verb phrases act as relative clauses.

Verbs in various languages

 * Ancient Greek verbs
 * Basque verbs
 * Bulgarian verbs
 * Chinese verbs
 * English verbs
 * Finnish verb conjugation
 * French verbs
 * German verbs
 * Germanic verbs
 * Hebrew verb conjugation
 * Hungarian verbs
 * Ilokano verbs
 * Irish verbs
 * Italian verbs
 * Japanese consonant and vowel verbs
 * Japanese verb conjugations
 * Korean verbs
 * Latin verbs
 * Persian verbs
 * Portuguese verb conjugation
 * Proto-Indo-European verb
 * Romance verbs
 * Romanian verbs
 * Sanskrit verbs
 * Sesotho verbs
 * Slovene verbs
 * Spanish verbs
 * Tigrinya verbs

Grammar

 * Auxiliary verb
 * Grammar
 * Grammatical aspect
 * Grammatical mood
 * Grammatical tense
 * Grammatical voice
 * Performative utterance
 * Phrasal verb
 * Phrase structure rules
 * Sentence (linguistics)
 * Syntax
 * Tense–aspect–mood
 * Transitivity (grammatical category)
 * Verb argument
 * Verb framing
 * Verbification
 * Verb phrase

Other

 * Le Train de Nulle Part: A 233-page book without a single verb.
 * Oh, with the verbing!