Arguing for Frege’s Fundamental Principle

Saul Kripke’s puzzle about belief demonstrates the lack of soundness of the traditional argument for the Fregean fundamental principle that the sentences ‘S believes that a is F’ and ‘S believes that b is F’ can differ in truth value even if a =b. This principle is a crucial premise in the traditional Fregean argument for the existence of semantically relevant senses, individuative elements of beliefs that are sensitive to our varying conceptions of what the beliefs are about. Joseph Owens has offered a new argument for this fundamental principle, one that is not subject to Kripke’s criticisms. I argue that even though Owens’ argument avoids Kripke’s criticisms, it has other flaws.