The argumentative theory of reasoning suggests that the main function of human reasoning is to argue: to find arguments to convince others, and to evaluate others' arguments to be convinced when warranted. Support for this theory has come so far from reviewing work in several domains of psychology. Here I will present novel experimental evidence supporting the theory's predictions: 1) argumentative competence is universal and early developing; 2) the improvement of performance in group discussion stems from sound argumentative competence; 3) there is an asymmetry in the way people evaluate their own and other people's arguments.