IS

Is is the third-person singular present tense form of the English verb be. It functions as a copular or auxiliary verb, linking a subject to a subject complement (such as a noun, pronoun, or adjective) or helping form verb tenses. In simple clauses, it expresses identity, property, or class membership: "The cat is hungry." It is used with he, she, it, or singular nouns. The other present-tense forms are am and are.

Etymology: Is originated in Old English as is, from Proto-Germanic *ist-, related to the German ist, Dutch is, and to the Indo-European cognates Latin est and Greek esti. The common root is reconstructed in Proto-Indo-European as *h₁és-ti, meaning "is" or "exists."

Grammar and usage: As a copula, "is" does not convey lexical action but links the subject with a predicate, such as an adjective, noun phrase, or clause. It can also function as an auxiliary in continuous (present progressive) constructions: "She is running." In passive voice, "is" combines with a past participle: "The song is sung every night." It participates in existential "There is/There are" constructions to indicate existence.

Other notes: Contractions "it's" for "it is" or "it has" are common; negation is formed with "isn't" or "is not"; questions are formed by inversion: "Is she coming?" The form "is" is part of a larger be-verb system with irregular forms (am, is, are; was, were; been; being).