Jean-Étienne Esquirol, working in the tradition of Philippe Pinel, helped formalize one of the most enduring distinctions in psychiatry: the difference between hallucinations and illusions, a concept that remains foundational to accurate diagnosis today. Misunderstanding this distinction can contribute to misclassification of perceptual experiences, inappropriate treatment, and missed underlying causes, particularly delirium, substance- or medication-related states, neurologic conditions, and se