Dialogical history of a logical fallacy spontaneously produced during a predictive medicine consultation. Role of the causal connective Puisque in a discussion

•A case study of conditional reasoning and logical fallacy in a dialogue.•Emergence and failure to resolve a fallacy in a dialogue of genetic counseling.•The pivotal role of the connector puisque in a discussion.

This article presents the dialogical history of the production and the contesting of logical fallacies in a natural dialogue stemming from a Genetic Counseling for Predictive Testing consultation. These logical fallacies are errors in reasoning that are well-known in psychology and rhetoric: « affirming the consequent » and « negating the antecedent ». The authors construct a formal model of this dialogue which explains why the fallacy appears and why corrective attempts ultimately fail. They show that the causal connective puisque is an essential operator of the studied dialogue.