Probabilities, Indicatives, and Relevance

This chapter combines topic-sensitivity and probabilities to provide an account of the acceptability conditions of (simple) indicative conditionals, i.e. indicatives with no further indicatives embedded in the antecedent or consequent. The account is in the spirit of the so-called Adams’ Thesis, in that the acceptability of a simple indicative is tied to the corresponding conditional probability; and in line with the Ramsey Test, whereby we assess conditionals by evaluating the consequent on the supposition of the antecedent. But it fixes the empirical and theoretical shortcomings of Adams’ Thesis by adding a relevance constraint for acceptability, where relevance is understood, again, as topic-sensitivity: we accept a simple indicative ‘If φ, then ψ’ to the extent that p(ψ|φ), the conditional probability of ψ given φ, is high, provided ψ is fully on-topic with respect to the topic of φ, plus that of background assumptions which matter for getting the consequent. The chapter presents a probabilistic logic for simple indicatives in terms of Popper functions, arguing that its (in)validities are both plausible and in line with empirical results on how people reason with conditionals.