Learnings: The Four Humours
The humour blood was connected to the element air; blood was thought to control someone's happiness and cheerfulness.
Yellow bile was connected to fire; it drove a person's anger and impulsiveness.
Black bile was connected to earth; it brought out melancholy and anxiety.
Last but not least, phlegm, connected to water, was responsible for self-control and apathy.
A person's humours could influnce their mood and behavior. Sad all the time? They might have too much black bile. Angry at the slightest thing? Too much yellow bile.
The theory of the Four Humours shows how medieval scholars saw the world as deeply interconnected. As seen in this 15th-century diagram, these thinkers understood humans to be a microcosm of the entire universe; every element in existence could be observed within a single human being.