From the time of the ancient Greeks, philosophers had been fascinated by the basic question of the nature of matter. Empedocles suggested that all matter was made up of four basic "roots" or elements (earth, air, fire, and water) and two basic forces, harmony and discord. Later writers, including Aristotle, argued that the four elements themselves expressed combinations of more basic qualities: hot, cold, dry, and moist.

The planets shared the same four primary qualities as all created matter: hot, cold, dry, moist. Thus in the illustration of the spheres, each planet has its combination; the problem of dealing with seven known planets and only four qualities was solved thus:

Saturn cold and dry
Jupiter hot and moist
Mars hot and dry (extreme)
The Sun hot and dry (moderate)
Venus cold and moist (extreme)
Mercury hot with hot, cold with cold, etc.
The Moon cold and moist (moderate)

Gendered planets

A further neat division was made between the male and the female. The male's natural temperament was hot and dry (Mars, warlike, in extreme; the sun, in moderation); the female was cold and moist (Venus or the moon).