Memorable Passages-11: From THE STORY OF PHILOSOPHY by Will Durant

Human behavior, says Plato, flows from three main sources: desire, emotion, and knowledge. ... Desire has its  seat in the loins.  It is a bursting reservoir of energy, fundamentally sexual.  Emotion has its seat in the heart, in the flow and force of the blood;  it is the organic resonance of experience and desire.  Knowledge has its seat in the head; it is the eye of desire, and can become the pilot of the soul.

These powers and qualities are all in all men, but in diverse degrees....

And last are the few whose delight is in meditation and undrestanding; who yearn not for goods, nor for victory, but for knowledge; who leave both market and battlefield to lose themselves in the quiet clarity of secluded thought; whose will is a light rather than a fire, whose haven is not power but truth; these are the men of wisdom, who stand aside unused by the world.

Now just as effective individual action implies that desire, though warmed with emotion, is guided by knowledge, so in the perfect state, the individual forces would produce but they would not rule; the military forces would protect but they would not rule; the forces of knowledge and science and philosophy would be nourished and protected, and they would rule.  Unguided by knowledge, the people are a multitude without order; like desires in disarray: the people need the guidance of philosophers as desires need the enlightenment of knowledge.  "Ruin comes when the trader, whose heart, is lifted up by wealth, becomes ruler";  or when the general uses his army to establish a military dictatorship.  The producer is at his best in the economic field, the warrior is at his best in battle; they are both at their worst in public office; and in their crude hands politics submerges statesmanship.  For statesmanship is a science and an art; one must have lived for it and been long prepared.  Only a philosopher-king is fit to guide a nation.  "Until philosophers are kings, or the kings and princes of this world have the spirit and power of philosophy, and wisdom and political leadership meet in the same man, ... cities will never cease from ill, nor the human race".   This is the keystone of the arch of Plator's thought.

- From THE STORY OF PHILOSOPHY by WILL DURANT (The Lives and Opinions of the Greater Philosophers)

Chapter I : PLATO

Section VI : THE PSYCHOLOGICAL PROBLEM  - Pages 22-23