Rawls theory of justice:

Rawls'  most famous work,  A  Theory  of  Justice  (1871),  provides an introduction to this  body  of  thought as well  as some of  its  implications for ethics. Like  many  philosophers  before him,  Rawls focused  upon  justice because of its substantive importance for organizing and governing society. The problem, however, involves defining what that term means theoretically (i.e.,  speculatively about organising and governing society)  and  practically (i.e.,  the consequences for people and their lives).

Generally speaking, justice can be defined in one of two ways. One definition emphasises an individual's merit or  lack of  it. According to this definition, each individual must be treated exactly as one deserves. This "meri{  theory" of  justice, reflecting utilitarian ethics, uses  merit  to determine just  how individual members of society will be rewarded or punished based solely upon whether one's conduct is useful or harmful to a society. The "need  theory" of justice, who assumes that individual members of the society should help those other members who are most  in need  so  as to  redress their disadvantages, reflects the influence of  natural  \law  theory.  In  this  view,  "doing good" dictates that every member of  society recognise that  need  entitles the most disadvantaged  to  some sort  of  special  consideration and that the more advantaged must compensate  the  disadvantaged with the  goal  of  bringing them up to an acceptable level of advantage.

Attempting to balance the demands  posed  by  these  rival  theories, Rawls maintained that inequalities  in  society can only  be  justified if  they  produce increased benefits for the entire society and only  if those previously the most disadvantaged members  of  society are  no  worse  off  as  a result of  any inequality.  An  inequality, then,  is justified if it contributes to social utility, as the merit theory asserts. But, at the same time, Rawls asserted, priority must be  given  to the needs of  the  least advantaged, as the needs theory asserts.

Thus, differential rewards are allowed to the advantaged members of society but  not  because  of  any  merit  on  their part. These rewards are tolerated because  they  provide an incentive for  the advantaged, which ultimately will prove  beneficial  to  society  (e.g.,  taxing  the  advantaged with the  goal  of redistributing the wealth to provide for the least advantaged).