Workshop on Modus Ponens

Dates: May 26-27 2016

 

• Justin Bledin (Johns Hopkins) • Modus Ponens Defended (Again)
  Abstract

  In a 2015 paper, I defended modus ponens for the indicative conditional against three attacks by McGee [1985], Kolodny and MacFarlane [2010], and Willer [2010]. In this talk, I present an updated version of part of this defense.

• John Cantwell (KTH Royal Institute of Technology) • The logic of the indicative conditional
  Abstract

  A global expressivist analysis of the indicative conditional is sketched alongside a model-theoretical semantics that takes `truth relative to an assumption' to be the core semantic notion. The semantic analysis - a semantic rendition of the Ramsey Test -- is originally due to McGee and is reminiscent of Kratzer's semantics for the indicative conditional. The resulting logic does not validate modus ponens. It is argued that although a conditional expresses the same proposition when evaluated categorically and when evaluated relative to an assumption, its truth value can change within the context of an assumption, and this is what explains the failure of modus ponens.

• Nate Charlow (Toronto) • Another Counterexample to Modus Ponens
  Abstract

  If Modus Ponens Is Valid, You Should Take Up Smoking

• Vladan Djordjevic (Belgrade) • Assumptions, Hypotheses and Antecedents
  Abstract

  The distinction between the three notions from the title is about the difference between arguments and conditionals (premises and antecedents) and about a further difference between two kinds of arguments (two kinds of premises - assumptions and hypotheses). The difference is easily made in artificial languages, and we are familiar with it from our first logic courses (although not necessarily under those names, since there is no standard terminology for the distinction). I will claim that there are ordinary language counterparts of the three notions, and I will propose definitions for them in pragmatic terms. Then I will apply the definitions to try to explain away some philosophical problems or paradoxes: the direct argument, a standard argument for fatalism, McGee's counterexample to modus ponens, the Ramsey+Moore=Good argument, the miner's paradox, and a recent counterexample to modus tollens.

• Alex Silk (Michigan) • Cancelled
• Una Stojnic (Rutgers) • One's Modus Ponens: Modality, Coherence and Logic
  Abstract

  Recently, there has been a shift away from traditional truth-conditional accounts of meaning towards non-truth-conditional ones, e.g., expressivism, relativism and certain forms of dynamic semantics. Fueling this trend is some puzzling behavior of modal discourse. One particularly surprising manifestation of such behavior is the alleged failure of some of the most entrenched classical rules of inference; viz., modus ponens and modus tollens. These revisionary, non-truth-conditional accounts tout these failures, and the alleged tension between the behavior of modal vocabulary and classical logic, as data in support of their departure from tradition, since the revisionary semantics invalidate some of these patterns. I, instead, offer a semantics for modality with the resources to accommodate the puzzling data while preserving classical logic, thus affirming the tradition that modals express ordinary truth-conditional content. My account shows that the real lesson of the apparent counterexamples is not the one the critics draw, but rather one they missed: namely, that there are linguistic mechanisms, reflected in the logical form, that affect the interpretation of modal language in a context in a systematic and precise way, which have to be captured by any adequate semantic account of the interaction between discourse context and modal vocabulary. The semantic theory I develop specifies these mechanisms and captures precisely how they affect the interpretation of modals in a context, and do so in a way that both explains the appearance of the putative counterexamples and preserves classical logic.