Illusions in reasoning about consistency

Reasoners succumb to predictable illusions in evaluating whether sets of as sertions are consistent. We report two studies of this computationally intr actable task of "satisfiability." The results show that as the number of po ssibilities compatible with the assertions increases, the difficulty of the task increases, and that reasoners represent what is true according to ass ertions, not what is false. This procedure avoids overloading memory, but i t yields illusions of consistency and of inconsistency. These illusions mod ify our picture of human rationality.