In psychiatric research a patient's rationalizing is often considered as a logical process, belonging to higher order functions, and measurable through strategizing, planning and certain aspects of IQ. However, it seems that the concept of rationality has more nuances in it self. We wish to introduce the distinction of a logical deductive rationality vs. a more fluid, inductive, ecologically and experientially bounded rationality. We postulate this as being highly relevant, when testing for characteristics of rationality in schizophrenia.

Our central hypothesis about schizophrenic rationality or reasoning is that it differs from that of healthy controls. We hypothesize that testing rationality in a new way, using our distinction of the rationality-concept, will shed some light on cognitive aspects of the phenomenologically described schizophrenic perplexity or “loss of common sense” as the central autistic feature of the illness.

The basis for the idea and development of the test, are the empirical findings by Kahnemann & Tversky and the Max Planck group led by Gerd Gigerenzer. One of their central explanatory models of healthy rationalizing is that people naturally take ecological and experiential information into account, and one of the core features of the schizophrenia might be that it does not happen sufficiently.

We aim to test if people with schizophrenia (n = 30) have a deficit of practical, milieu-bounded, “common sense” rationality, and preservation or accentuation of theoretical rationality, which, compared to healthy controls (n = 30), could help explaining the autistic “loss of common sense”.