The field of didactics in Swedish social science and civics is narrow, with particularly few studies based in the practise of social science and civics. The study aims to present more knowledge about what the ability to reason about justice in civics consists of, and how it is constituted in and by the practise of civics education. The study is based upon empirical data from seven interviews and three Learning Studies (Pang & Marton, 2003; Pang & Lo, 2011) about justice in civics. The study examines a learning object – the ability to reason about justice in civics – with the use of a phenomenographic approach. The ability to reason about justice is explored through analysing both students’ conceptions of justice, and students’ conceptions of what it is to reason in civic. These conceptions are related to each other and to the practise of civics, focusing on communicative actions that enables students to distinguish critical aspects of the ability to reason about justice. This can be described as an alternative way to examine an object of learning in its different aspects and in relation to how it is constituted in the educational social science/civics practise.