In his works he analysed, creating the unique and unprecedented genre of "biological essays", the great human passions through historical characters, and their psychic and physiopathologic features: shyness in his book Amiel, resentment in Tiberio, power in The Count-Duke of Olivares, intrigue and treason in politics in Antonio Pérez (one of the makers of the Spanish "black legend"), the "donjuanism" in Don Juan, etc.
