The people who built the idea and when: Hippocrates and Galen, Avicenna, Hildegard of Bingen, the School of Salerno, and where the four humors began.
Robert Burton spent thirty years on a thousand pages about his own black bile, and wrote plainly that he wrote of melancholy by being busy to avoid melancholy. It is the largest book anyone produced inside the humoral system.
Vesalius could not find Galen's anatomy in a human body in 1543, and Harvey showed that blood circulates in 1628. Physicians went on bleeding patients for another two hundred years, and the reason why is the interesting part.
On a Greek island around the fifth century BC, and in Rome six centuries later, two physicians who never met gave us the language of temperament we still use.
A teenage boy in Bukhara talks his way into a royal library, then grows up to write the medical book that Europe and the Islamic world studied for six hundred years.
In 1798 Kant kept the four temperaments and threw out the fluids underneath them. Wundt and then Eysenck turned what he left behind into two crossed axes, which is how Galen's four names ended up on a modern personality diagram.
From Hippocrates to Avicenna to the Renaissance: how a theory of bodily fluids became a lasting map of human character.
On the Tyrrhenian coast south of Naples, a town of doctors became the first medical school in western Europe, the place where Galen's humors came home to the Latin world.
One of the few women whose scientific voice survives from the twelfth century, Hildegard of Bingen wrote about the four humors and bound them to her own greening vision of body, soul, and world.