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). 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.
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.
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, Bosnian, Serbian, 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.
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, she go is not (except in the subjunctive, as "They requested that she go with them"). Instead, a special form of the verb to go has to be used to produce she 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, she may), and the verb to be has an additional form am that can only be used with the pronoun I as the subject.