In his Tetrasomia, or Doctrine of the Four Elements, Empedocles described these elements not only as physical manifestations or material substances, but also as spiritual essences. He associated these elements with four Greek gods and goddesses - air with Zeus, earth with Hera, fire with Hades, and water with Nestis (believed to be Persephone):
Now hear the fourfold roots of everything: Enlivening Hera, Hades, shining Zeus And Nestis, moistening mortal springs with tears.
Empedocles explained that there are two great living forces in the universe, which he called Love (Philotês) and Strife (Neikos) and assigned to Aphrodite and Ares. According to Hesiod, the Goddess Love and the God Strife, offspring of Night (Nux), were ancient deities, predating the Olympians. The original Greek golden age was the Reign of Aphrodite, when all things were united and Love permeated the length and breadth of the well-rounded cosmic sphere. But Strife, as the River Styx surrounding the Sphere, broke its Unity, and cleaved the One into Many. It divided the four elements, which ever since combine and separate under the opposing actions of Love and Strife to produce the changing world with its manifold objects and qualities. As Heraclitus said, "Through Strife all things come into being." Empedocles said that Strife also divided the one immortal soul of Love into many individual souls, each comprising both Love and Strife in some proportion; these immortal souls are reborn time and again into mortal bodies, which are animated by mortal souls compounded from the four elements.
Another Greek philosopher/scientist who subscribed to the idea of four personality types was the physician Hippocrates. Rather than consider them to be "roots" or elements, he viewed them as bodily fluids or humors. Fire is akin to his conceptualization of blood (active, enthusiastic), earth to phlegm (apathetic and sluggish), air to yellow bile (irritable, changeable), and water to black bile (sad, brooding).
