Question

Beliefs

The strongest and most widespread belief was that of the four
and four
elements. The humours are
and the seat of all these fluids was thought to be
the liver. The four humours are blood, phlegm, yellow bile, and black bile.
Blood meant that -
Phlegm meant that -
Yellow bile meant that -
Black bile meant that -

Answer 1

At some point people believed that the production of certain bodily fluids or Humours could determine human behavior. Those humours are:

Blood ⇒ Sanguine

Blood represented a sanguine nature which means that the person goo-natured, energetic and positive. They are optimistic about life and so can rarely be depressed.

Phlegm ⇒ Phlegmatic.

Phlegm represented introverts as they referred to reserved and calm people.

Yellow bile ⇒ Choleric.

Yellow bile came to represent bad and ill tempered people who were prone to anger and aggression.

Black bile ⇒ Melancholic

Black bile was for people who were depressed and generally sad about life.