The object of this essay is to examine Amartia Sen’s approach to the justification of substantive rights pointed out in the third chapter of ‘Development as Freedom’ and his critique of the priority of formal freedoms in rawlsian theory. He points out a conflict between liberties (formal freedoms) and freedoms (material freedoms). This opposition will be confronted with Herbert Hart’s polemic in the third part of ‘Essays in Jurisprudence and philosophy’, where he points out a problem of Rawls’ formulation in not reconciling the admission of private property as a basic freedom with the principle of maximum equal freedom. The problem is whether the Sen model better addresses this issue. Our positive hypothesis. By establishing a small number of basic freedoms, Rawls treated the right as a mere formal guarantee. Consequently, the right to private ownership of large portions of land and the extensive control by private individuals over the financial system and over major industrial, commercial, and service goods, in the absence of any greater or consistent justification, end up envisioned by something equivalent to a self-justified natural right. As Marx said, it is not scientifically possible to conceal the original fact of the conquest of private property by covering it up under the diaphanous cloak of natural law, inasmuch as, to oppose the ‘natural right of a few’ it would be enough for the previously dispossessed majority to gather sufficient strength to impose a ‘natural right’ of the reconquest of usurpation. As for the method, it is an exclusively bibliographical research, which can be based, in a merely incidental way, on empirical data.