Counterfactual Diagnosis: Bridging Disease and Illness Through Two-Level Reasoning

This essay introduces a new way to connect biological explanations of illness with patient experience using counterfactual reasoning. Building on Boorse's theory of disease and phenomenology, the author offers a two-level diagnostic model. At the objective level, clinicians use counterfactuals to understand causes. At the subjective level, patients describe their illness by imagining what their life would be like if they weren't sick. By showing that both clinicians and patients use "what-if" thinking-though in different ways-the model suggests a shared logical structure between clinical evidence and personal experience. This method keeps diagnosis evidence-based while also taking the patient's story seriously. The result is an approach that may help address both the biological causes and the life changes illness brings and provide tools for a more thoughtful and patient-centered approach to diagnosis.