Abstract

In The Logical Basis of Metaphysics, Dummett articulates and develops his “fundamental assumption” that the introduction rules for a logical constant determine its meaning. According to Dummett, logical laws in harmony with the introduction rules are justified, while logical laws not in harmony with the introduction rules are unjustified. This powerful picture enables Dummett to criticise certain aspects of our linguistic practice, such as the Law of Excluded Middle and the metaphysics of realism he believes it embodies, as not remaining responsible to the meanings of the logical constants. Against Dummett's fundamental assumption, I bring to bear what in the Tractatus Wittgenstein describes as his “fundamental thought” that the logical constants do not represent. Properly understood, Wittgenstein's point is that since the logical constants may be eliminated from the propositional signs of a fully precise logical notation, the constants do not express meanings to which our use of expressions containing the constants is responsible. I then apply Wittgenstein's fundamental thought to Dummett's proof‐theoretic notation to show that far from determining the meanings of the logical constants, the introduction rules merely allow the constants to be edited from certain inferences, leaving Dummett with no semantic kernel with which to criticise other sentences or inferences featuring the constants. Thus, his picture of what it is to make clear the working of our language collapses.