ABSTRACT
The study of conditionals has always been a prominent part of the psychology of reasoning, as can be seen from the first introduction to the subject (Wason & Johnson-Laird, 1972) to the most recent (Manktelow, 2012), and understandably so. There is a philosophical view that a conditional, if p, then q, is nothing but an “inference ticket” for inferring q from p (Bennett, 2003, pp. 118-119). A conditional is seen as essentially an inference, and every inference can be expressed as a conditional. This suggestive “inference ticket” idea is far from a full theory, but conditionals and inferences are clearly so closely related that the psychology of reasoning could almost be thought of as equivalent to the psychology of conditionals. In this chapter, we will cover the discovery, by Wason (1966), of a most important fact about ordinary people’s evaluations of natural language indicative conditionals. They do not classify these conditionals as only true or false, but think of them as sometimes having a third value of some kind. We will explain what has become of this finding in the contemporary psychology of reasoning, and make recommendations for how it should be developed in the future.
