 Prawitz (1985; 2005) argues that  any formally suitable introduction rule can fix the meaning for a logical constant. On Prawitz’s view, the lesson we learn from Prior is that we cannot also stipulate an elimination rule, but must justify any proposed elimination rule by showing that there is a procedure for rearranging any direct proof of the premises of the elimination rule into a direct proof of the conclusion. Thus, we can stipulate the introduction rule for “tonk”, but must then content ourselves with the strongest elimination rule for which such a procedure is available: