Abstract

According to S. Kripke, an expression is rigid provided it refers to the same object in all possible worlds in which the object exists. On the other hand, H. Putnam claims that an expression is rigid provided it refers to the same object in all possible worlds in which it refers to anything at all. The paper shows that the two notions of rigidity are not equivalent because Putnam's rigidity is much broader than Kripke's; unlike Putnam's rigidity, Kripke's is interwoven with essentialism; and identity statements between rigid designators in Putnam's sense need not be necessarily true.