In 1970 Quine proposed what can be considered a challenge to any revisionist attempt in the realm of Logic: if the revisionist does not accept a classical principle, then he must attribute a different meaning to some of the concepts present in the principle. If the revisionist attributes new meanings to some of the concepts present in the classical principle, the revisionist logician and the classical logician are not talking about the same thing. If they are not talking about the same thing, there can be no conflict between them. In a recent paper, Dag Prawitz seems to agree with Quine, when he says: "When the classical and intuitionistic codifications attach different meanings to a constant, we need to use different symbols, and I shall use a subscript c for the classical meaning and i for the intuitionistic. The classical and intuitionistic constants can then have a peaceful coexistence in a language that contains both."

 

But, according to Prawitz, to assert that the classical and the intuitionistic codifications attach different meanings to some constant and to recognize the need to use different symbols corresponding to these different meanings is not a kind of trivial acceptance of Quine's position, for, as Prawitz puts it

"This does not imply that the classical meanings of these constants cannot be explained in the same general way as the intuitionistic meanings of the logical constants have been explained."

 

The aim of the present paper is twofold: [1] to investigate the proof theory for Prawitz' Ecumenical system and [2] to propose a truth-theoretical semantics for which Prawitz' system is sound and complete.