Every proposition consists of three parts: the Subject, the Predicate, and the copula.
"A System Of Logic, Ratiocinative And Inductive (Vol. 1 of 2)"
John Stuart Mill
The copula is the sign denoting that there is an affirmation or denial; and thereby enabling the hearer or reader to distinguish a proposition from any other kind of discourse.
"A System Of Logic, Ratiocinative And Inductive (Vol. 1 of 2)"
John Stuart Mill
Dismissing, for the present, the copula, of which more will be said hereafter, every proposition, then, consists of at least two names; brings together two names, in a particular manner.
"A System Of Logic, Ratiocinative And Inductive (Vol. 1 of 2)"
John Stuart Mill