International audienceWhat does “reasoning” mean? What is its purpose? And, how does it function? This chapter defines reasoning and the distinction between deductive and inductive reasoning. Secondly, the argumentative theory of reasoning proposed by Mercier and Sperber (2011) is presented to understand the purpose of the reasoning. This theory postulates that its function is to convince others and to evaluate information received when someone tries to convince another. Thirdly, the authors focus on the intervention model of reasoning developed by Evans (2011) to try to understand how the reasoning functions. This model is derived from dual-process theories and proposes a distinction between two types of processing in reasoning. The last p...