|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.|
Books on Amazon
Copula/Frege: E.g. "The sky is blue." - contrast: Equation: "The number of Jupiter’s moons equals four." - The four contains nothing of Jupiter and Moon.
Equal Sign/"="/Frege/(s): links objects, not concepts or predicates with properties. - By contrast, Copula/(s): links an object with a concept.
The copula does not express identity: "sky = blue", but a simple "is". (The predicate is enclosed) - right: "The sky is a blue thing": "A is a B". (> indefinite article).
Die Grundlagen der Arithmetik Stuttgart 1987
Funktion, Begriff, Bedeutung Göttingen 1994
Logische Untersuchungen Göttingen 1993