From the Wikipedia article on Vilfredo Pareto, his sociological schema for human behavior –

Pareto used his time at Céligny to write his Trattato di sociologia generale, which was finally published, after wartime delays, in 1916. This was his great sociological masterpiece. He explains how human action can be neatly reduced to residue and derivation. People act on the basis of non-logical sentiments (residues) and invent justifications for them afterwards (derivations). The derivation is thus just the content and form of the ideology itself. But the residues are the real underlying problem, the particular cause of the squabbles that leads to the “circulation of élites”. The underlying residue, he thought, was the only proper object of sociological enquiry.

Residues are non-logical sentiments, rooted in the basic aspirations and drives of people. He identifies six classes of residues, all of which are present but unevenly distributed across people — so the population is always a heterogeneous, differentiated mass of different psychic-types. The most important residues are Class I the “instinct for combining” (innovation) and Class II, the “persistence of aggregates” (conservation). Class I types rule by guile, and are calculating, materialistic and innovating. Class II types rule by force and are more bureaucratic, idealistic and conservative.
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