The feasibility constraint on the concept of justice

There is a widespread belief that, conceptually, justice cannot require what we cannot achieve. This belief is sometimes used by defenders of so-called 'non-ideal theories of justice' to criticise so-called 'ideal theories of justice'. I refer to this claim as 'the feasibility constraint on the concept of justice' and argue against it. I point to its various implausible implications and contend that a willingness to apply the label 'unjust' to some regrettable situations that we cannot fix is going to enhance the action-guiding potential of a conception of justice, by providing an aspirational ideal. This is possible on the condition that, at all times, we cannot specify with certainty the limits of what is feasible for us collectively. The rejection of the feasibility constraint entails that there can be injustice without perpetrators; this is a theoretical price worth paying.