Humours 
 
Historical Background
The theory of humours originated in the ancient world.  The great 2nd century A.D. Roman physician Galen established a system that combined elements of anatomy, psychology, astrology, pharmacology, and just about every other area of knowledge to which the ancients had access. Little about the system had changed by Shakespeare’s time almost fifteen centuries later. The most famous treatment of the theory of humours in English was Robert Burton’s The Anatomy of Melancholy, and while this book did not appear until 1621 — five years after Shakespeare’s death — in truth it merely summarized material that was available in other sources, albeit in a more entertaining and comprehensive form than it had appeared before.
 
The Basics
The four humours were literally bodily fluids, but were associated with personality traits, which is why we still talk about someone being “good-humoured.” Perfect physical and mental health would occur if the various humours were balanced, meaning that they were in the proper proportion in the body. However, no one was ever thought to be perfectly balanced. Minor imbalances were associated with personality traits, whereas severe imbalances led to bodily illnesses and personality disorders. An excess of a humour could be treated by decreasing the amount of that humour in the system, for example by bleeding, diuretics, laxatives, or enemas.
 
Connections
This table shows some of the associations given to the humours
 
Humour
Blood
Phlegm or Pituita
Yellow Bile
Black Bile
Character Type
Sanguine
Phlegmatic
Choleric
Melancholic
Element
Air
Water
Fire
Earth
Planet (or luminary)
Jupiter
Moon
Mars
Saturn
Astrological Signs
Gemini, Libra, Aquarius
Cancer, Scorpio, Pisces
Aries, Leo, Sagittarius
Taurus, Virgo, Capricorn
Wind/Direction
South
East
West
North
Temperature/Moisture
Hot and Moist
Cold and Moist
Hot and Dry
Cold and Dry
Season
Spring
Winter
Summer
Autumn
Phase of Life
Adolescence
Childhood (also senility)
Adulthood
Old Age
Appearance
Large-framed, with a pink or red complexion
Fleshy and fair
Slim, wiry, red-haired
Slim, fair, not muscular
Appearance if out of balance
Fat, with a florid complexion
Fat and pale
Thin, color rises when angry
Thin, pale
Character Traits
Optimistic, cheerful, fun-loving, generous, amorous
Emotional, mild, passive, sensitive, intuitive
Ambitious, energetic, direct
Thoughtful, introspective, reflective
Character Traits if out of balance
Irresponsible, gluttonous, inebriate, lusty
Lazy, vulnerable, cowardly, excessively emotional
Violent, hot-tempered, unscrupulous, vengeful
Depressive, narcissistic, self-loathing

Yellow bile includes gall and urine; think of how we associate an easily annoyed or angered character as being “pissed-off” or “pissy.” Black bile includes feces, but also clotted blood.
Note that combination characters also exist.  For example, someone can be choleric-melancholic, or sanguine-choleric, and so on. In each case, that person would combine the qualities of both humours.
 
Shakespeare’s Characters

Many of Shakespeare’s characters recognizably represent a specific humour. Falstaff is the most famous sanguine character in literature.  Hamlet, of course, is the melancholy Dane. Laertes is obviously choleric, while he associates his sister Ophelia with “too much of water” — suggesting she is phlegmatic. Shakespeare also uses the references to humours for comedic effect. For example, after the play within the play, Guildenstern tells Hamlet that the King “Is in his retirement marvelous distempered.” Hamlet asks, “With drink?” (clearly playing dumb in order to make a pointed insult about Claudius, whom he considers a drunk), and Guildenstern replies, “No, my lord, with choler.” Hamlet then suggests Guildenstern should be giving this information to the king’s doctor, “for for me to put him to his purgation would no doubt plunge him into more choler”  (III.ii.327-34). The phrase “put him to his purgation” would, in this case, refer to catheterizing him (in Elizabethan times, this would involve inserting a thin metal rod up the urethra in order to relieve pressure in the bladder) which Hamlet says would certainly make him angrier. No doubt!