Conditional probability and pragmatic conditionals: Dissociating truth and effectiveness

Abstract

Abstract Recent research (e.g., Evans & Over, Citation2004) has provided support for the hypothesis that people evaluate the probability of conditional statements of the form if p then q as the conditional probability of q given p, P(q/p). The present paper extends this approach to pragmatic conditionals in the form of inducements (i.e., promises and threats) and advice (i.e., tips and warnings). In so doing, we demonstrate a distinction between the truth status of these conditionals and their effectiveness as speech acts. Specifically, while probability judgements of the truth of conditional inducements and advice are highly correlated with estimates of P(q/p), their perceived effectiveness in changing behaviour instead varies as a function of the conditional probability of q given not-p, P(q/∼p). Finally, we show that the conditional probability approach can be extended to predicting inference rates on a conditional reasoning task. Notes 1Oaksford and colleagues have recently used a similar method of calculating conditional probabilities from estimates of the four truth-table cases to successfully account for performance on another conditional reasoning task, namely the Wason selection task (e.g., Oaksford & Moussakowski, Citation2004; Oaksford & Wakefield, Citation2003). 2For the interested reader, mean inference rates for each conditional statement are presented in Appendix B. This appendix also shows, for each conditional, the four computed conditional probabilities. 3This pattern was obtained when each inference type was analysed separately, except that for both DA and AC, the valence factor was significant while the interaction did not reach significance. 4Indeed, the correlation between P(q/∼p) and behavioural effectiveness for advice (although non-significant) was in the positive direction. This positive correlation was, however, mostly due to one warning conditional; upon removal of this statement, this correlation was close to zero. 5To deal with the possibility of non-linearity, we applied a square root transformation to the truth variable. However, the correlation between behavioural effectiveness and truth ratings remained unchanged after this transformation. Additional informationNotes on contributorsEyvind Ohm The authors gratefully acknowledge an operating grant from Natural Science and Engineering Research Council of Canada (NSERC). We also would like to thank Jonathan Evans and three anonymous reviewers for their helpful comments on an earlier draft of this paper.