| Abstract: | A radical metaphysical theory typically comes packaged with a semantic theory that reconciles those radical claims with common sense. The metaphysical theory says what things exist and what their natures are, while the semantic theory specifies, in terms of these things, how we are to interpret everyday language. Thus may we “think with the learned, and speak with the vulgar.” This semantic accommodation of common sense, however, can end up undermining the very theory it is designed to protect. This paper is a case study, showing in detail how one popular version of temporal parts theory is self‐undermining. This raises the specter that the problem generalizes to other metaphysical theories. The traditional flavor of temporal parts theory, Worm Theory, claims that everyday objects are four‐dimensional space‐time worms. An alternative flavor, Slice Theory, claims that objects are not space‐time worms but are instead momentary slices of these worms. The differences, we find, are not nearly as great as advertised. In fact, the differences in the two metaphysical theories are entirely masked by compensating differences in the accompanying semantic theories. As a result, the two theories generate exactly the same truth conditions. Common sense says that I was born years ago. Slice Theory adopts a semantic theory that accommodates such claims, but in doing so, it also endorses the claim that I, like other everyday objects, persist and thus do not exist for a mere moment. That is, the metaphysical claims constitutive of Slice Theory are denied by the very semantic theory Slice Theory adopts to accommodate common sense. Slice Theory thus undermines itself. |
