A little amazingness I was reading last night!! Its Plato's allegory of the chariot. All these questions we tend to figure out, they've been study for so long, its just a matter of digging a bit into history! Enjoy!
Plato, in his dialogue, Phaedrus (sections 246a - 254e), uses the Chariot Allegory to explain his view of the human soul. He does this in the dialogue through the character of Socrates, who uses it in a discussion of the merit of Love as "divine madness".
Plato paints the picture of a Charioteer driving a chariot pulled by two horses. One horse is white and long necked, well bred, well behaved, and runs without a whip. The other is black and short-necked, badly bred, troublesome.
The Charioteer represents intellect, reason, or the part of the soul that must guide the soul to truth; the white horse represents rational or moral impulse or the positive part of passionate nature (e.g., righteous indignation); the black horse represents the soul's irrational passions, appetites, or concupiscent nature. The Charioteer directs the entire chariot/soul, trying to stop the horses from going different ways, and to proceed towards enlightenment.