As to the misconceptions: In the first place, the existence of "undecidable propositions" or "unsolvable problems" has only remote connections with the failure of excluded middle. More precisely, from the fact that a certain problem is unsolvable, one cannot infer that the affirmative and negative answers to that problem are both incorrect. Both Gödel's and Church's theorems were originally proved for systems with the excluded middle, i.e. for systems in which 'p or not p' is provable for every proposition 'p'; (...) though in the light of Gödel's theorem there are propositions 'p' such that neither 'p' nor 'not p' is provable in those systems. Careful distinction should be made between the following locutions. (shrink)

Our first aim is to make the study of informal notions of proof plausible. Put differently, since the raison d'étre of anything like existing proof theory seems to rest on such notions, the aim is nothing else but to make a case for proof theory; ...

A notation for the language of physics is given, and a system of axioms constructed. It is argued that from the standpoint of a 'realistic' ontology our method is preferable to Carnap's 'coordinate languages.' The primitive ideas are the part-whole relation μ and the set H of coordinate systems. Only such statements are intended in the axioms as are non-controversial; i.e. no open cosmological questions are prejudged.

CONSIDER A NON EMPTY BUT OTHERWISE ARBITRARY SET OF\nPROPERTIES CALLED OBSERVATION-PROPERTIES (O-PROPERTIES).\nCALL A PROPERTY P A MEANINGFUL PROPERTY (M-PROPERTY) IF IT\nIS EQUIVALENT TO A (FINITE OR INFINITE) DISJUNCTION OF\nO-PROPERTIES--I.E., A NECESSARY AND SUFFICIENT CONDITION\nFOR P IS THAT AT LEAST ONE OBSERVATION-PROPERTY IN A\nCERTAIN SET O(P) BE TRUE. OBVIOUSLY THE CONJUNCTION AND\nDISJUNCTION OF TWO M-PROPERTIES IS AN M-PROPERTY; IN\nGENERAL THE NEGATION OF AN M-PROPERTY IS NOT AN M-PROPERTY.\nHOWEVER WE CAN DEFINE THE PSEUDO NEGATION OF AN M-PROPERTY\nP AS THE POSSESSION OF SOME (...) O-PROPERTY INCOMPATIBLE WITH P.\nTHE ALGEBRA OF DISJUNCTION, CONJUNCTION AND PSEUDO NEGATION\nOF M-PROPERTIES TURNS OUT TO START IN THE SAME RELATION TO\nBOOLEAN ALGEBRA AS INTUITIONISTIC LOGIC (NOT 3-VALUED\nLOGIC) DOES TO CLASSICAL LOGIC, AND SUGGESTS THEREFORE THAT\nINTUITIONISTIC RATHER THAN 3-VALUED LOGIC IS THE\nAPPROPRIATE FORMALISM TO DEAL WITH THE PARADOXES OF THE\nBALD MAN, THE HEAP, ETC. (shrink)