抽象允许一种自由，而具象有时无法做到。

人是万物的尺度：对于存在的事物，它们存在；对于不存在的事物，它们不存在。

经验只是我们给错误取的名字。

To every action there is always opposed an equal reaction； or， the mutual actions of two bodies upon each other are always equal， and directed to contrary parts.