chapter  Chapter Three
30 Pages

Suppositional reasoning: if and or

WithJonathan St B. T. Evans

Hypothetical thinking involves the imagination of possibilities and, according to the theory advanced here, typically consists of singular mental simulations. In this chapter, I will focus on the thinking in which a person introduces a temporary belief or supposition as the foundation of such a mental simulation. Such suppositional reasoning is most often stimulated in natural language exchanges by conditional statements (or conditionals for short) that have the form “if p then q”. For example, a statement such as “if you want to impress the boss you should arrive early in the mornings” is intended to make the listener reflect upon their behaviour and consider the benefits (and costs) of changing it. Such conditional thinking based on a single supposition is very natural, according to hypothetical thinking theory. Much more difficult are tasks requiring more than one simulation based upon different suppositions as some use of the disjunctive form “p or q” require. Hence, psychological studies of reasoning with both “if” and “or” will be examined in this chapter.