Copula

copula

Logic the often unexpressed link between the subject and predicate terms of a categorial proposition, as are in all men are mortal

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Copula 

an auxiliary grammatical element of a compound predicate having a weakened lexical meaning and serving to express merely grammatical categories of the predicate, the lexical meaning being expressed by a nonconjugated, usually nominal, element. The verb “to be” is used as a copula in many languages. The presence of a copula may be obligatory, as in English and French; optional, as in Russian and Hungarian; determined by the type of nominal predicate, as in Swahili; or determined by the semantic character of the sentence, as in Khmer. Certain verbs besides “to be” can function as copulas; these verbs, which introduce an additional nuance to the meaning of the elements linked by the verb, include the Russian nachinat’ (“to begin”), stanovit’sia (“to become”), and delat’ (“to do,” “to make”).