Vilfredo Pareto, the élite theorist and the leader of the “political realism” school, considered the human society as a system in equilibrium. Consequently according to him, men had to search for the life forces that constitute it, separate it and at last reassemble it. They are the manifestation of the individual instincts or feelings, classified by Pareto as “remnants”, “derivations” and “derivate” and so on, expressions of “social heterogeneity”, that is expressions of antithesis and separation between the élites and the masses. The “remnants theory” has always been the vexata quaestio of the interprets of Pareto. This essay gives a psychological interpretation of this theory, despite the several scholars from McDougall onwards who stated that Pareto didn’t know the psychology at all.