In this article we analyze the theories of Hobbes contractualism, which postulates that human beings must comply with minimum agreed duties, and Rawls social justice, which imposes the duty of mutual aid. The above with the purpose of demonstrating how solidarity, as a way of adhering to the causes of others, stands as a concept that justifies the JDLS. This work is developed thanks to an analytical and interpretative methodology of the mentioned philosophical currents and it was found that these theoretical perspectives coincide in relation to the need for the members of a state to help each other. These findings suggest that solidarity is, precisely, one of the justifying reasons for this democratic judgment, since the adherence to the causes of others that this implies, means care on the part of the other members of society and implies that the citizenship, in that care action, perform certain actions related to that JDLS.