上句见：Day317
The Story of Philosophy《哲学的故事》第1章Plato第6节VI. The Psychological Problem第3段第1句：

Human behavior, says Plato, flows from three main sources: desire, emotion, and knowledge. Desire, appetite, impulse, instinct — these are one; emotion, spirit, ambition, courage — these are one; knowledge, thought, intellect, reason — these are one. Desire has its seat in the loins; it is 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.
浙江大学译本：柏拉图认为，人之行为有三种根源：欲望、情感和知识。

解析

1、Human behavior, says Plato, flows from three main sources: desire, emotion, and knowledge.
柏拉图认为；人之行为主要源自三种：欲望、情感和知识。
flow from: to be a natural result of something源自；由……引起
A Jedi's strength flows from the Force.绝地武士的力量来源于原力。《电影世界深度游》

这段开始讲柏拉图有名的“灵魂论”。这句开始定基调，或是准则，人的行为是有哪三种决定的。我们接下来可以关注柏拉图如何基于这个来解决问题。

柏拉图认为；人之行为主要源自三种：欲望、情感和知识。