My last post was about the link between the words melancholy and choler, which are based on the Greek word for bile. Melancholy and choler were associated with black bile and yellow bile, respectively, which were two of the four humors in a system of ancient and medieval medicine. The humors were different fluids in the human body, and diseases were believed to arise from imbalances among them.
The English word humor in this sense came from French, which got it from Latin, specifically umor, or body fluid, which is related to the verb umere, or to be moist. The word humor in this sense is related to humid, which also has to do with dampness or moisture. Although the concept of four humors is a thing of the past, we still talk about the vitreous humor (literally glassy fluid), the gel-like substance that fills the eyeball between the lens and the retina.
The system of four humors was embedded in a complex web of associations. Each humor had its season and its organ in the body, and was thought to have attributes described by various permutations of the characteristics hot, cold, wet, and dry. For example, yellow bile, or choler, was thought to be hot, dry, and associated with summer and the spleen. (I haven't been able to find out what it means for a fluid to be dry; perhaps this is some sort of figurative use, as in dry wine, but I don't know.)
This system was intended to provide guidelines for treating illness. It was eventually extended to personality types, or temperaments. Each temperament was seen as a particular blending of the four humors; the word comes from the Latin temperare, meaning to mix. Galen, who devised this system, identified nine temperaments; the four that are the most familiar today are the ones that he called choleric, melancholic, sanguine, and phlegmatic, each associated with one of the humors.
Sanguine comes from the Latin word for blood, sanguis, because the sanguine temperament was believed to result from an excess of blood. A sanguine person is an upbeat happy sort. We still use this word to mean optimistic or cheerful, although we no longer think it has anything to do with a healthy ruddy complexion. You also see this Latin root in sanguinary, which means involving bloodshed or bloodthirsty. I was puzzled by the similarity between these words until I learned how they're connected.
Phlegm is pretty much the phlegm we know, the only one of the humors to have made it down to today under the same name. Oddly enough, phlegm was thought to be cold and moist and associated with winter, but the Greek root from which it originally sprang, phlégma, has to do with inflammation and heat, which I suppose makes sense in the context of upper respiratory illnesses in which fever and phlegm coincide. The phlegmatic temperament was believed to be calm, even stolid or sluggish. The word is still used to describe calm, unemotional people.
In fact, although the humoral system of medicine and the concept of four temperaments have long since been overtaken by more sophisticated approaches1, the names of all four temperaments linger on as adjectives that describe people or attitudes. What is most interesting to me is that although we don't think of optimism in terms of blood any more, or depression or calmness in terms of black bile or phlegm, the link connecting the bitter fluid bile with irritability or anger remains strong. You can talk about the bilious rant you had to listen to, read a comments thread on some news article and marvel at the bile-filled invective, or vent your spleen. (Just don't vent it here, please.)
1 Well, more or less. The idea of four temperaments lives on, in mutated form, in some current personality systems, although psychology has pretty much settled on five aspects of personality known as the Big Five personality traits.↩