On the Source of Human Irrationality

Reasoning and decision making are error prone. This is often attributed to a fast, phylogenetically old System 1. It is striking, however, that perceptuo-motor decision making in humans and animals is rational. These results are consistent with perceptuo-motor strategies emerging in Bayesian brain theory that also appear in human data selection. People seem to have access, although limited, to unconscious generative models that can generalise to explain other verbal reasoning results. Error does not emerge predominantly from System 1, but rather seems to emerge from the later evolved System 2 that involves working memory and language. However language also sows the seeds of error correction by moving reasoning into the social domain. This reversal of roles suggests key areas of theoretical integration and new empirical directions.