Research into doctoral supervision has increased rapidly over the last decades, yet our understanding of how doctoral students learn scientific thinking from supervision is limited. Most studies are based on interviews with little work being reported that is based on observation of actual supervision. While joint supervision has become widely used, its learning dynamics remains under-researched and this paper aims to address these gaps in research by exploring learning opportunities in doctoral supervision with two supervisors. The study explores how the tensions in scientific discussion between supervisors can become learning opportunities. We combine two different theoretical perspectives, using participation and positioning theory as a sociocultural perspective and variation theory as an individual constructivist perspective on learning. Based on our analysis of a complex episode we suggest that multiple supervisors can add value to supervision through authentic practice of scientific argumentation.