Speaker: Franz Berto (University of St Andrews)
Date and Time: Thursday, May 22nd 2025, 16:30-18:00
Venue: ILLC Seminar Room F1.15, Science Park 107 and online.
Title: Counterfactual Supposition.
Abstract. The promising idea behind the Ramsey Test is that we assess ‘A > B’, where ‘>’ is some conditional operator, by judging the believability or likelihood of B on the supposition A. Lewis and Gärdenfors taught us that the Test clashes with AGM-style qualitative belief revision as well as Bayesian conditionalization for credences. But it has been long been spotted that AGM and conditionalization can govern indicative supposition (What is the case if A is the case?), not subjunctive or counterfactual supposition (What would be/have been the case if A was/had been the case?). And if, as has also been proposed, the latter is governed by (a) KGM (Katsuno-Grahne-Mendelzon)-style belief revision (which can be recaptured in modal-epistemic logic) in a qualitative setting, and (b) Lewisian imaging for credences – then everything falls into place: we have Ramsey Tests mapping the standard Lewis-Stalnaker variably strict counterfactual conditional to such revision procedures (a) and (b). Moreover, as shown in this talk, (a) and (b) are essentially the same procedure, declined in a qualitative and probabilistic setting respectively. And this neat package is evidence that we assess counterfactuals by subjunctive supposition, in a perfectly consistent way.