On deliberation in the public debate, Rawls’ approach known as "justice as fairness" has been much more commented that the "difference principle" emerged from there as a major result: even though based on an equal initial position, "justice as fairness" paradoxically justifies an essential benchmark in the debate on inequalities. Indeed, the "difference principle" compresses many issues: distinguishing between naturel and social matters which both contribute to inequalities, defining a level of permitted inequalities we should have to tolerate not as just but effective ones, preserving market incentives in so far they contribute to value creation, which has later to be redistributed. The paper explores all these questions, that concern the philosophical-economic rationality of the principle and its political-societal applicability as well. In conclusion, its contribution to the debate on inequalities, which is beyond all doubt, seems rather economic than philosophical and is based on a liberal presupposition, which is rarely identified and recognised.