Sustainability, understood as intergenerational social justice, poses a series of theoretical and practical difficulties. Among the former ones, is the problem of thinking about the future as a source of rights and obligations, as well as neoliberal criticism of the concept of social justice. Among the latter ones, is the development of an individualistic and selfish subjectivity that puts the idea of the social contract in crisis. However, this idea is also questioned, from another perspective, by what has been left "outside" the contract: the rest of nature, the domestic space and the non-citizens. Ecological thinking, feminism and recognition question the foundation of the social contract. Their demands can be met by rescuing the concept of fraternity, understood both in its conflictive dimension and in what it implies in the search for harmony.