The long lasting tradition linking the cosmos and the analogical microcosm of man, which founded the medical practice of Hippocrates or Galen and their followers, was still alive when Shakespeare started writing for the stage.
According to this cosmo-physiology, continued in Burton’s Anatomy of Melancholy, the four humours were to the human microcosm what the four elements were to the cosmos. This implied that each individual could be ruled by a dominant passion following the material combinations of humours into a prevailing "temper". Yet another tradition, also inherited from the classic world, and which conflicted with the material determinism of the humours, posed freedom of choice as necessary to the control over passion and therefore to the foundation of ethics. Galen’s answer to the challenge was a subtle psychosomatic approach positing that psychic freedom was dependent on a thorough knowledge of the somatic determinism of the humours.
This conflicting relation between the humours and the control of passions is also central to the representation of characters on stage: mimesis or the imitation of the motivations in men’s actions aims at catharsis, i.e. the effects of humours shown there might or should suggest the cure to overcome the passions that originate in them. On the Elizabethan stage, the "characters" (a word also used by Galen in his psychosomatic approach) partake of a typology of "humours" (dominant in satirical comedies). These characters may also prove victims of the passions that these humours occasion, and become tragic heroes as, blindly or bravely, they try to fight them back. Richard III, "determined to be a villain" by physical determinism, is compelled to psychic cruelty; Falstaff is swayed by the Moon to steal; and both are linked to the typology of medieval Vice, whereas Prince Hall, who emerges as the future Sun King from the "moist humours" of the clouds, and gaining drier humours, finds the way to become "temperate" like his father, Henry IV, in complete contrast to Hotspur, overcome by an excess of bile, whether dry and hot (choler) or cold and moist (melancholy), unable to strike a balance. Hamlet himself is both a melancholy "humour" and a tragic hero who discovers patience and masters his passions in the end. Echoes of this complex relation between the humours and the passions can be found throughout Burton’s Anatomy of Melancholy, showing the lasting psychosomatic or "humorous" approach to the passions. However, in a play like Othello, although strikingly relying on the convulsive "passion" of jealousy, Shakespeare seems to be breaking new grounds regarding dramatic characterisation and the representation of the passions: he manages to dissociate the "humour" predisposing to a "passion" only the better to isolate its pure mechanism. Othello, a man who comes from a dry climate and is free, as such, of all alienating "humours", once artificially moved to jealousy, could betray all the visible signs of this passion; whereas the only real "humour" in the tragedy is Iago, jealous from birth (at least from his very first words in the tragedy), his motiveless but unavoidable jealousy creating his "motiveless malignity". Only Iago’s stagecraft, no longer of devilish origin as in the case of Richard III, motivates the tragedy: the hypocrite actor, "honest, honest Iago", allows Shakespeare to experiment on stage the effects of pure passion, freed from the archaic determinism of the humours. With Othello, Shakespeare seems to point at further developments in characterisation and at new stage techniques, paving the way for the emancipation of new aesthetics.