Kenneth Arrow is a founder of the social choice theory as well as a main developer of modern theories of market economies. Moral obligations and social norms are at the core of Arrow's ethical considerations to understand and overcome his well-known impossibility theorem of preference aggregation. Interestingly, he thinks that moral obligations and social norms are very important to overcome failures of market economies. Also, he proposed some interaction between public policies and evolution of social norms. Here, we can find a consistent and systematic thinking of Arrow's ethical considerations, which might be overlooked in spite of its importance. We believe that Arrow has political philosophy (or a theory of justice), which is quite useful to understand recent developments of behavioral economics and theories of non-market economies. Arrow's thought is totally different from Amartya Sen and John Rawls, which are dominant in modern theories of justice. Arrow's approach can shed some new lights on the subject of social justice.