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Meta language / Prior: Problem: "I say something wrong" cannot be the only thing I say - then a meta language is necessary, otherwise follows an absurdity: I could choose a short time interval in which I could say nothing else - also: the language in which the theorems are expressed, can not be the same as the language used in some other opportunities to do so -a hierarchy is possible without meta language : e.g. "N": "something that Prior says between t and t is not the case": then: N is a true sentence if and only if ... something is not the case - ((s) without quotation marks) - e.g. VsMeta language. "I’ll be damned if grass is pink."- ((s) quasi-"operator") - Prior: "isolation" through "I’ll be" - solution: meta-part of the language (isolated), no complete meta language.
Objects of thought Oxford 1971
Arthur N. Prior
Papers on Time and Tense 2nd Edition Oxford 2003