In linguistics, conjugation (/ˌkɒndʒʊˈɡeɪʃən/^[1][2]) is the creation of derived forms of a verb from its principal parts by inflection (alteration of form according to rules of grammar). For instance, the verb break can be conjugated to form the words break, breaks, broke, broken and breaking. While English has a relatively simple conjugation, other languages such as French and Arabic or Spanish are more complex, with each verb having dozens of conjugated forms. Some languages such as Georgian and Basque have highly complex conjugation systems with hundreds of possible conjugations for every verb.

Verbs may inflect for grammatical categories such as person, number, gender, case, tense, aspect, mood, voice, possession, definiteness, politeness, causativity, clusivity, interrogatives, transitivity, valency, polarity, telicity, volition, mirativity, evidentiality, animacy, associativity,^[3] pluractionality, and reciprocity. Verbs may also be affected by agreement, polypersonal agreement, incorporation, noun class, noun classifiers, and verb classifiers.^[4] Agglutinative and polysynthetic languages tend to have the most complex conjugations, albeit some fusional languages such as Archi can also have extremely complex conjugation. Typically the principal parts are the root and/or several modifications of it (stems). All the different forms of the same verb constitute a lexeme, and the canonical form of the verb that is conventionally used to represent that lexeme (as seen in dictionary entries) is called a lemma.

The term conjugation is applied only to the inflection of verbs, and not of other parts of speech (inflection of nouns and adjectives is known as declension)^{[citation needed]}. Also it is often restricted to denoting the formation of finite forms of a verb – these may be referred to as conjugated forms, as opposed to non-finite forms, such as the infinitive or gerund, which tend not to be marked for most of the grammatical categories^{[citation needed]}.

Conjugation is also the traditional name for a group of verbs that share a similar conjugation pattern in a particular language (a verb class). For example, Latin is said to have four conjugations of verbs. This means that any regular Latin verb can be conjugated in any person, number, tense, mood, and voice by knowing which of the four conjugation groups it belongs to, and its principal parts. A verb that does not follow all of the standard conjugation patterns of the language is said to be an irregular verb. The system of all conjugated variants of a particular verb or class of verbs is called a verb paradigm; this may be presented in the form of a conjugation table.

Verbal agreement, or concord, is a morpho-syntactic construct in which properties of the subject and/or objects of a verb are indicated by the verb form. Verbs are then said to agree with their subjects (resp. objects).

Many English verbs exhibit subject agreement of the following sort: whereas I go, you go, we go, they go are all grammatical in standard English, he go is not (except in the subjunctive, as "They requested that he go with them"). Instead, a special form of the verb to go has to be used to produce he goes. On the other hand I goes, you goes etc. are not grammatical in standard English. (Things are different in some English dialects that lack agreement.) A few English verbs have no special forms that indicate subject agreement (I may, you may, he may), and the verb to be has an additional form am that can only be used with the pronoun I as the subject.

Verbs in written French exhibit more intensive agreement morphology than English verbs: je suis (I am), tu es ("you are", singular informal), elle est (she is), nous sommes (we are), vous êtes ("you are", plural), ils sont (they are). Historically, English used to have a similar verbal paradigm. Some historic verb forms are used by Shakespeare as slightly archaic or more formal variants (I do, thou dost, he doth, typically used by nobility) of the modern forms.

Some languages with verbal agreement can leave certain subjects implicit when the subject is fully determined by the verb form. In Spanish, for instance, subject pronouns do not need to be explicitly present, but in French, its close relative, they are obligatory. The Spanish equivalent to the French je suis (I am) can be simply soy (lit. "am"). The pronoun yo (I) in the explicit form yo soy is used only for emphasis or to clear ambiguity in complex texts.

Some languages have a richer agreement system in which verbs agree also with some or all of their objects. Ubykh exhibits verbal agreement for the subject, direct object, indirect object, benefaction and ablative objects (a.w3.s.xe.n.t'u.n, you gave it to him for me).

Basque can show agreement not only for subject, direct object and indirect object but it also can exhibit agreement for the listener as the implicit benefactor: autoa ekarri digute means "they brought us the car" (neuter agreement for the listener), but autoa ekarri ziguten means "they brought us the car" (agreement for feminine singular listener).

Languages with a rich agreement morphology facilitate relatively free word order without leading to increased ambiguity. The canonical word order in Basque is subject–object–verb, but all permutations of subject, verb and object are permitted.

These common grammatical categories affect how verbs can be conjugated:

• Finite verb forms:
  • Grammatical person
  • Grammatical number
  • Grammatical gender
  • Grammatical tense
  • Grammatical aspect
  • Grammatical mood
  • Grammatical voice
• Non-finite verb forms.

Here are other factors that may affect conjugation:

• Degree of formality (see T–V distinction, Honorific speech in Japanese, Korean speech levels)
• Clusivity (of personal pronouns)
• Transitivity
• Valency

Indo-European languages usually inflect verbs for several grammatical categories in complex paradigms, although some, like English, have simplified verb conjugation to a large extent. Below is the conjugation of the verb to be in the present tense (of the infinitive, if it exists, and indicative moods), in English, German, Yiddish, Dutch, Afrikaans, Icelandic, Faroese, Swedish, Norwegian, Latvian, Bulgarian, Serbo-Croatian, Polish, Slovenian, Macedonian, Urdu or Hindi, Persian, Latin, French, Italian, Spanish, Portuguese, Russian, Albanian, Armenian, Irish, Ukrainian, Ancient Attic Greek and Modern Greek. This is usually the most irregular verb. The similarities in corresponding verb forms may be noticed. Some of the conjugations may be disused, like the English thou-form, or have additional meanings, like the English you-form, which can also stand for second person singular or be impersonal.

¹ Archaic, poetical; used only with the pronoun 'thou'.

² In Flemish dialects.

³ In the bokmål written standard.

⁴ In the nynorsk written standard. vera and vere are both alternate forms.

⁵ Archaic

⁶ Attic.

⁷ 'eínai' is only used as a noun ("being, existence").

⁸ Ptc: qenë.

⁹ In the Tosk and Geg dialects, respectively.

¹⁰ Existential: هست (hæst) has another meaning. Usage of (æ) is considered to be colloquial, now. See, Indo-European copula

¹¹ With the Singular they 3rd person pronoun.

¹² Bengali verbs are further conjugated according to formality. There are three verb forms for 2nd person pronouns: হও (hôo, familiar), হোস (hoś, very familiar) and হন (hôn, polite). Also two forms for 3rd person pronouns: হয় (hôy, familiar) and হন (hôn, polite). Plural verb forms are exact same as singular.

¹³ Valencian.

¹⁴ Western varieties only.

• Agreement (linguistics)
• Declension (nouns, adjectives, etc.)
• Inflection
• Redundancy (linguistics)
• Screeve
• Strong inflection
• Verb
• Verb argument
• Volition (linguistics)
• Weak inflection