Abstract

There are largely separate psychological literatures on logical reasoning and on decision making. This division has limited psychological theories in both areas, and particularly held up the study of ordinary deductive reasoning. People do not ordinarily reason from a restricted set of arbitrary assumptions taken, in effect, to be certainly true. Much more often, they try to perform inferences from all their relevant beliefs, holding few of these with absolute confidence, or they perform inferences from statements made to them, and treat few of these as absolutely reliable. They recognise that their premises have some degree of probability or uncertainty, and they consequently have more or less confidence in them. This affects their confidence in, and probability judgements about, their conclusions. People also face the problem of getting evidence to assess how probable or uncertain their premises are, and this calls for further probability judgements, as well as utility judgements and decision making. Much better understanding of people's deductive reasoning in realistic contexts will be achieved by integrating research on it with research on decision making and probability and utility judgments.