Ramsey’s Test, Adams’ Thesis, and Left-Nested Conditionals Richard Dietz Institute of Philosophy, University of Leuven richard.dietz@hiw.kuleuven.be Igor Douven Institute of Philosophy, University of Leuven igor.douven@hiw.kuleuven.be Abstract Adams famously suggested that the acceptability of any indicative conditional whose antecedent and consequent are both factive sentences amounts to the subjective conditional probability of the consequent given the antecedent. The received view has it that this thesis offers an adequate partial explication of Ram- sey’s test, which characterizes graded acceptability for conditionals in terms of hypothetical updates on the antecedent. Some results in van Fraassen [1976] may raise hope that this explicatory approach to Ramsey’s test is extendible to left- nested conditionals, that is, conditionals whose antecedent is itself conditional in form. We argue that this interpretation of van Fraassen’s results is to be re- jected. Specifically, we provide an argument from material inadequacy against a generalization of Adams’ thesis for left-nested conditionals. Ernest Adams’ well-known thesis on the acceptability of conditionals says that the de- gree of acceptability for a given conditional amounts to the corresponding conditional probability of the consequent given the antecedent. 1 Notwithstanding the open ques- tion of whether ordinary speakers’ normative assessments lend evidential support to the thesis, it seems to still be common ground in the philosophical community that it provides an adequate explication of Ramsey’s test, which gives an informal char- acterization of acceptability for conditionals. Even that granted, it is to be stressed that Adams’ thesis provides at best only a partial account of graded acceptability for conditionals. For it concerns only simple conditionals, that is, conditionals whose an- tecedent and consequent are factive sentences, that is, sentences which are atoms or obtainable from atoms by means of Boolean connectives. Some results in van Fraassen [1976] may raise hope that Adams’ explicatory approach is extendible to instances of Ramsey’s test for left-nested conditionals, that is, conditionals whose antecedent is itself conditional in form. We argue that this interpretation of van Fraassen’s results is to be rejected. In particular, we show that, first, whatever type of probabilism for languages with a conditional that one may plausibly consider, conditional probability 1 For simplicity, in what follows we omit reference to utterances of sentences and just refer to sen- tences. Unless specified otherwise, we refer to indicative conditionals throughout as conditionals 1