《汉书·志·食货志上》
因此英明的君王界定百姓，就建筑城邑让他们居住，在井田中建屋庐使他们平均，开设市场使他们进行财物流通，设立学校来教育他们；士、农、工、商，四种人有自己的事业。
是以圣王域民，筑城郭以居之；制庐井以均之；开市肆以通之；设庠序以教之；士、农、工、商，四人有业。
Therefore, wise kings define the people, build cities for them to live in, build houses in the fields so that they are evenly distributed, open up markets for them to trade in, and establish schools to educate them; scholars, farmers, craftsmen, and merchants, the four classes of people have their own professions.