Initial teacher education in Western societies is shaped by a market-oriented view of education that fosters relationships based on convenience and self-interest. As teacher educators, we seek to promote a communitarian ethics grounded in responsibility, commitment, and care for others. In this context, this article examines how such ethics emerge in an activity that encourages forms of relating different from market logic. Based on a dialectical-materialist analysis of an episode involving four pre-service teachers and a teacher educator solving a task on equivalence and fraction ordering, we identified dialectical opposites that express the unity of contradictory features of communitarian ethics. The results show that this ethics emerged from the way participants dealt with features such as relinquishment of voice, exclusion, and lack of empathy.