ON THE MENTAL REPRESENTATION OF CONDITIONAL SENTENCES

Four experiments are reported which attempt to externalize subjects' m ental representation of conditional sentences, using novel research me thods. In Experiment 1, subjects were shown arrays of coloured shapes and asked to rate the degree to which they appeared to be true of cond itional statements such as ''If the figure is green then it is a trian gle''. The arrays contained different distributions of the four logica lly possible cases in which the antecedent or consequent is true or fa lse: TT, TF, FT, and FF. For example, a blue triangle would be FT for the conditional quoted above. In Experiments 2 to 4, subjects were abl e to construct their own arrays to make conditionals either true or fa lse with any distribution of the four cases they wished to choose. The presence and absence of negative components was varied, as was the fa rm of the conditional, being either ''if then'' as above or ''only if' ': ''The figure is green only if it is a triangle''. The first finding was that subjects represent conditionals in fuzzy way: conditionals t hat include some counter-example TF cases (Experiment 1) may be rated as true, and such cases are often included when subjects construct an array to make the rule true (Experiments 2 to 4). Other findings inclu ded a strong tendency to include psychologically irrelevant FT and FF cases in constructed arrays, presumably to show that conditional state ments only apply some of the time. A tendency to construct cases in li ne with the ''matching bias'' reported on analogous tasks in the liter ature was found, but only in Experiment 4, where the number of symbols available to construct each case was controlled. The findings are dis cussed in relation to the major contemporary theories of conditional r easoning based upon inference rules and mental models, neither of whic h can account for all the results.