In the 5th century BC Hippocrates believed that the four elements of nature (earth, water, wind, fire) exist in proportions not only in the world but also in the human body, and correspond to specific functions:
- The earth is dry and cold, and corresponds to black bile
- The water is wet and cold, and represents the phlegm
- The air is wet and warm, and corresponds to the blood
- The fire is dry and warm, and corresponds to the yellow bile
When in harmony, man is a perfectly harmonious individual.
Generally, however, one of the four elements of nature dominates and affects the character, health, and body shape.
Thus, the four types of people emerge:
- The earth (black bile) forms the melancholic
- the water (phlegm) the phlegmatic
- the air (blood) the bloody
- and the fire (yellow bile) the choleric.
So, according to Hippocrates:
- the melancholic has a tendency to be sad and depressed for the slightest hindrance he/she has
- the phlegmatic is usually apathetic, calm, and generally introverted
- the bloody is optimistic and intelligent, and hardly spoils his/her mood
- the choleric is irritable and dynamic.
Aristotle, in his Natural philosophy, attempted to analyze the character classes based on external characteristics but takes a great deal of account the race of individuals. The physiognomy was adopted by almost all peoples, but it has enjoyed a special performance in China. But there the elements are not four but five (fire, earth, water, metal, wood), so the same applies to human categories.