Many physicians distrust philosophical discussions and dismiss them as having no practical value. Nevertheless, if we are to gain further insight into the meaning and limitations of medical diagnosis, we must discard our prejudices and review some of the philosophical foundations on which diagnosis rests. Without doubt the most important philosophical questions for our review involve the theory of universals and the closely related problems of classification, definition, nomenclature, induction, and deduction.
The theory of universals1 attempts to define the relationship between particulars, as found in individual observation, and general ideas or universals. Consideration of the theory of universals is important in many fields, and its particular significance for medicine lies in the way it forces us to focus on a frequent dichotomy in our thought. Every time a physician thinks about a patient or makes a diagnosis, he must consider the patient as an individual and at the