The causes of inequality are many and varied, and may be broadly grouped into three factors. The first is social condition or family background. In China, for example, someone born and bred in the city usually earns a higher income and enjoys better social services. The second is aptitude. The cleverer or stronger ones usually earn more and enjoy better conditions than the lesser endowed. The final one is ambition and diligence. All things being equal, someone who aims higher and works harder often earns more.

　　虽然导致不平等的原因很多，但我们可以大体上把它们分为三类。一类是社会条件或家庭出身，例如在中国，与出生于贫困农村的人们相比，一个出生在大城市的人通常拥有更多的收入和更好的社会处境。另外一类是自然天赋，有些人天生聪明或健壮，有些人则天生愚笨或孱弱，前者一般也会比后者拥有更多的收入并处于更好的状况。最后一类是抱负和努力程度，在其他条件相同的情况下，更有抱负和更努力的人们通常也会有更多的收入。