<論文>双子地球通信

Abstract

双子地球の思考実験によるヒラリー・パトナムの議論では，「私は水が飲みたい」という私の思考の意味は，私の心的内容だけでは決まらず，私の置かれている外部環境をも参照されなければならないとされる．本稿では双子地球という概念装置自体への批判は差し控えるものの，双子地球の思考実験から意味の外在主義を導くパトナムの議論が妥当でないことが示される．というのも，パトナムの双子地球論証はそれ自身地球語で書かれざるをえないにもかかわらず，その点に無自覚であるからだ．本稿は，双子地球を用いた議論からは，意味の外在主義は肯定も否定もされないのだということを論ずる．

When I think, “I want to drink water, ” how is the meaning of what I thought determined? It is natural to believe that the meaning of what I say is determined only by my mind. However, a strong argument against this theory exists in Hilary Putnam's Twin-Earth argument. Putnam advocates for “semantic externalism” using this argument. According to semantic externalism, “water” in my mind cannot be determined solely by my mental state ; my external environment also determines its meaning. Semantic externalism has several adverse consequences. For example, if one's mind alone does not determine what one is thinking, one may not know what one is thinking. Thus, semantic externalism is a serious issue. This study argues that the Twin-Earth argument developed by Putnam is incorrect because the idea of a “twin earth” contains a claim inconsistent with semantic externalism. However, this does not imply that the Twin-Earth concept itself is inappropriate. In this case any argument that uses it would be invalid. Thus, we explain that the notion of the Twin-Earth is consistent with the practice of reading. By reworking the Twin-Earth argument, we demonstrate that it cannot be used to derive semantic externalism. However, this study aims not to argue for a particular theory of meaning but rather to point out that any argument for a theory of meaning must be made using language.