Developed by ancient Greek thinkers in the 5th century BCE, the theory of the four humors continued to develop during the ...

Throughout human history, people have tried to classify each other by describing personality types. The ancient Greeks described the four humors, a theory that personality results from a mixture of ...

Galen, a Greek physician, is born. He develops the theory of the four "humors": blood, phlegm, yellow bile and black bile. Good health is thought to result from a balance of the humors ...

This is true no matter the arena or walk of life. When our knowledge of the human body extended no further than the four humors, any barber could apply medicinal leeches or perform annual bleedings.