This is a facepalm “Duh” moment, I hear this criticism all the time but it does not mean that “logic” depends on “set theory”. There is a confusion here between what can be STATED and what can be KNOWN. The criticism only has any force if you think that all “logical truths” ought to be recognizable so that they can be effectively enumerated. But the critics don’t mind that for any effective enumeration of theorems of arithmetic, there are true statements about integers that won’t be included—we can’t KNOW all the true facts about integers, so the criticism of second-order logic boils down to saying that you don’t like using the word “logic” to be applied to any system powerful enough to EXPRESS quantified statements about the integers, but only to systems weak enough that all their consequences can be enumerated.
This demand is unreasonable. Even if logic is only about “correct reasoning”, the usual framework given by SOL does not presume any dubious principles of reasoning and ZF proves its consistency. The existence of propositions which are not deductively settled by that framework but which can be given mathematical interpretations means nothing more than that our repertoire of “techniques of correct reasoning”, which has grown over the centuries, isn’t necessarily finalized.
This is a facepalm “Duh” moment, I hear this criticism all the time but it does not mean that “logic” depends on “set theory”. There is a confusion here between what can be STATED and what can be KNOWN. The criticism only has any force if you think that all “logical truths” ought to be recognizable so that they can be effectively enumerated. But the critics don’t mind that for any effective enumeration of theorems of arithmetic, there are true statements about integers that won’t be included—we can’t KNOW all the true facts about integers, so the criticism of second-order logic boils down to saying that you don’t like using the word “logic” to be applied to any system powerful enough to EXPRESS quantified statements about the integers, but only to systems weak enough that all their consequences can be enumerated.
This demand is unreasonable. Even if logic is only about “correct reasoning”, the usual framework given by SOL does not presume any dubious principles of reasoning and ZF proves its consistency. The existence of propositions which are not deductively settled by that framework but which can be given mathematical interpretations means nothing more than that our repertoire of “techniques of correct reasoning”, which has grown over the centuries, isn’t necessarily finalized.