Everything has a unity between inside and outside. Inevitable is within, liberty is outside of nature. Nature is an object of humans, so nature is both inside and outside of human. The exchange of humans is a natural exchange, an exchange is both inside and outside of human, a inevitable and liberty exchange. The inevitable of nature becomes man's liberty, while the liberty of nature becomes the inevitable of human. Liberty on the inside, inevitable on the outside, humans carry the instincts of a species; Inevitably on the inside, liberty on the outside, human is the truth and creativity. Human liberty has become an inevitable part of society, that is the standard. Slaves to the inevitable of nature and standard of society, people are be liberty and irresponsible, humans have the instincts of a species. Humans having liberty are responsible. Human life is an exchange between inevitable and liberty manifests itself in different means and purposes, making human life a difference between truth and falsehood, just and unjust, good and evil, noble and low, rich and poor.