|Copula: a copula is a connection of the subject with a predicate within a sentence or statement. E.g. the sky is blue. The copula is not the same as the "is" of identity.|
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A) Identity: e.g. "Cicero is Tullius"
B) Predication: e.g. "Cicero is a Roman".
Stabilizing function: the difference consists in the different stabilization functions of the lowest type of "is" not in a different lexicon sense.
R. G. Millikan
Language, Thought, and Other Biological Categories: New Foundations for Realism Cambridge 1987