- #36
nomadreid
Gold Member
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- 229
It has always seemed to me that a rule of inference occupied a funny place somewhere between semantics and higher-level syntax , between model and theory.
On one hand, it refers to the truth values of statements, hence attached to the semantics of the theory.
On the other hand, it is equivalent to a higher-order statement quantifying over the sentences of the theory, with the truth values now being constants in a corresponding higher-order theory.
So, clearly not belonging to the theory but also not belonging to an interpretation in the sense of sets which satisfy sentences, it seems to inhabit a third level somewhere.
I haven't come to terms with where that third level belongs. Just saying that it is metalogical seems to be hand-waving.
On one hand, it refers to the truth values of statements, hence attached to the semantics of the theory.
On the other hand, it is equivalent to a higher-order statement quantifying over the sentences of the theory, with the truth values now being constants in a corresponding higher-order theory.
So, clearly not belonging to the theory but also not belonging to an interpretation in the sense of sets which satisfy sentences, it seems to inhabit a third level somewhere.
I haven't come to terms with where that third level belongs. Just saying that it is metalogical seems to be hand-waving.