Let’s examine social justice in the context of equal participation with a special attention on people with disability! The enquiry embedded in negative initial conditions, as in real life people with disability have initial disadvantages, follows a thought experiment about the original position with a specific aim: how can we change a situation that represents an obviously discriminative system towards people with disability through universal rules, and make it justful without decision makers themselves becoming maintainers of this system’s discrimination towards people with disability? The argumentation of the thought experiment is built on theories of John Rawls and Martha C. Nussbaum, such as the set-up conditions of the original position, rational self-interest, universal rules on the one hand, and capability, dependency, individual peculiarities and outer conditions on the other hand. Furthermore, more authors are lined up on behalf of several social disciplines to enrich the argumentation with new perspectives on the social environment of disability. The thought experiment was tested in 32 test groups with 421 participants between December 2018 and April 2023. As test results show, Rawlsian rational self-interest and the veil of ignorance contribute less to ensure equal participation for people with disability than the solution of Martha Nussbaum’s approach that takes notice of human conditions, relations and social diversity.