Russia,according to Mr.Medvedev, must move from an economy based on natural resources to innovation and high tech, which will require democratization.

VOA: standard.2009.11.12

But he says, "Others believe that the distinction between master and slave is not natural, " but is based on force or coercion."

但他还说：，“有些人却不认为,介于主奴间的区别是自然的，而是基于武力或威吓的缘故“

耶鲁公开课 - 政治哲学导论课程节选

That was the natural thing to do given the character of life, which was based upon farming, if you leave you lose your farm, and based upon the difficulty of transportation.

生活的意义就是定居一处,种田养家,离开了这片土地,就失去了食物的来源,另外,古时的交通非常落后

耶鲁公开课 - 古希腊历史简介课程节选