Suppose that 2 competing norms. N-1 and N-2, can be identified such that a given person's response can be interpreted as correct according to N-1 but incorrect according to N-2. Which of these two norms, if any. should one use to interpret such a response? In this article, we seek to address this fundamental problem by studying individual variation in the interpretation of conditionals by establishing individual profiles of the participants based on their case judgments and reflective attitudes. To investigate participants' reflective attitudes, we introduce a new experimental paradigm called the storekeeping task. As a case study, we identify the participants who follow the suppositional theory of conditionals (N-1) versus inferentialism (N-2) and investigate to what extent internally consistent competence models can be reconstructed for the participants on this basis. After extensive empirical investigations, an apparent reasoning error with and-to-if inferences was found in 1 of these 2 groups. The implications of this case study for debates on the proper role of normative considerations in psychology are discussed.