An injustice is tolerable only when it is necessary to avoid an even greater injustice.
Ideally a just constitution would be a just procedure arranged to insure a just outcome.
The principles of justice are chosen behind a veil of ignorance.
The strength of the claims of formal justice, of obedience to system, clearly depend upon the substantive justice of institutions and the possibilities of their reform.
There are various ways you might define the common good, but that would be one way you could do it.
At best the principles that economists have supposed the choices of rational individuals to satisfy can be presented as guidelines for us to consider when we make our decisions.