Any comprehensive sociology is based on the idea of universal human rationality. Its analyzes are usually based on ordinary psychology. This article defends the idea that this is not sufficient, especially when it comes to the area of belief. Indeed, rationality is limited in three ways (in dimension, representation and cognition) that must be used by the comprehensive method. If one considers sociology as a discipline that examines the hybridization of both social variables and mental invariants, the latter invariants stern not only from instrumental rationality or logical consistency, but can also be based on shared cognitive heuristics.