As M. Say truly remarks, it is on the very elements of our subject that illustration is most usefully bestowed, since the greatest errors which prevail in it may be traced to the want of a thorough mastery over the elementary ideas.

• 正如萨伊先生所指出的，用实例来说明政治经济学的基本原理是非常有用的，因为政治经济学中一些常见的大错误，都可以归因于没有透彻地理解基本概念。