The Dennes Room

Event Detail

Fri Apr 2, 2010
60 Evans Hall, 4:10–6 PM
Logic Colloquium
Seth Yalcin (UC Berkeley)
Modus Tollens Denied

I present and defend a number of counterexamples to Modus Tollens, construing Modus Tollens as a pattern of inference expressible in ordinary language. I ask what these counterexamples teach us about the meaning of conditional sentences and about the concept of logical consequence appropriate to understanding natural language inference. Since under classical assumptions, Modus Tollens can be proved from Modus Ponens, I ask in particular whether we should abandon Modus Ponens (as Vann McGee has independently argued we should), or give up aspects of the classical reasoning that allows us to prove Modus Tollens from Modus Ponens. I develop the latter approach.