The dominating model of social justice in democratic countries can be characterized by a combination of equality of opportunities and merit. But how can its internal validity be guaranteed as equality is grounded on a principle of identity between retributions, and merit on a principle of proportionality between contribution and retribution ? If we look at the data from two international surveys (EVS, 1999 ; ISSP - Social inequalities, 1999), we can also observe that the model has a strong external validity. The wide consensus over items related to the reduction of inequalities and to the recognition of merit makes it possible to identify a cumulative conception of social justice. The model therefore appears to be congruent with an extended conception of justice : fairness can be introduced as a counterclaim, compensating for the dysfunctional consequences of a meritocratical allocation of resources.