[Formal thinking, logical-discursive operations and schizophrenia: experimental study of a clinical case]

This study, based on a single case experimental design, examined logical reasoning in a schizophrenic meeting the DSM-III criteria. The quantitative assessment carried out by 32 psychiatrists on a rating scale for logical thinking disorders (nine items, six points) of the retranscribed clinical interview showed 1. that the assessments varied in a statistically significant way according to items and psychiatrists, and that these variations were independent of their degree of experience--the correlations between the different items of the rating scale proved to be weak and not significantly different from zero; and 2. the study of the most contradictory statements carried out by a logician using reasoning analysis procedures concluded that there were in fact logical relationships between the subjects the schizophrenic talked about. The results are discussed in relation to the methodology of assessing formal thought in schizophrenia.