Introduction. In modern scientific research, the thought experiment remains relevant in both natural and social sciences. Its use in theoretical legal science is particularly significant, as it compensates for the impossibility of practical verification of hypotheses by real experiment. One of the most striking examples of the application of the thought experiment is Lon Fuller’s “The Case of the Speluncean Explorers”, published in 1949. In the experiment the author simulates a judicial process, imitating a conflict of different approaches to understanding and interpreting law. Theoretical analysis. As part of this thought experiment, Fuller examines the case of the forced murder of a man by a group of speleologists in an emergency situation. The arguments of the five fictional judges demonstrate different doctrinal approaches: formalism, legal process, natural law, legal realism, and an emotional-relativistic approach. This experiment not only raises the question of the nature of justice and moral responsibility, but also reflects the real contradictions in the legal concepts of the mid-20th century. By joining Fuller’s experiment, the reader is forced to solve them independently, which is how the heuristic nature of the methodological tool chosen by the thinker manifests itself. Еmpirical analysis. The authors show that the “The Case of the Speluncean Explorers” is actively used to discuss theoretical and ethical aspects of law. The positions of the judges were analyzed, their strengths and weaknesses were identified. Special attention is paid to the emotional factor that prevents the achievement of a unanimous decision. Results. Fuller’s thought experiment effectively reveals the drama of legal decision-making, stimulates deep reflection on the moral aspects of law, and demonstrates the importance of integrating different approaches for an adequate understanding of the essence of law and justice.