Alexander L. Gungov
St. Kliment Ohridski University of Sofia
15 bul. Tsar Osvoboditel, 1504 Sofi a Center, Sofia, Bulgaria

Examining diagnostics in logical terms, attention is usually paid to the interaction between deductive and inductive reasoning. This article discusses Ch.S. Peirce’s theory of abductive inference in the clinical diagnosis. The process of diagnostics is seen as a logical transition from the effect (patient’s symptoms and signs) to the cause (the current health disorder), which is the direction common to abductive reasoning. For Peirce, abduction is performed through transposition of the conclusion and the major premise in the categorical syllogism or, in his later writings, of the result and the rule. An emphasis is put on the ampliative leap from the premise (individual clinical signs and symptoms) to the conclusion (particular diagnosis) abduction features; the universal rule (the nosologial unit) meditates between the individual clinical picture and the particular patient’s diagnosis.

The abductive inference draws on Kantian view on reflective judgment and G.B. Vico’s ideas about imaginative universals. Reflective judgment aims at identifying a concept for some sensible data, whereas imaginative universals are not rational concepts but contain general characteristics like the regular concepts; formation of an imaginative universal resembles giving a diagnosis where is performed an imagination driven combination of general elements of the relevant nosological unit and individual clinical signs and symptoms. Attention is also paid to the principles of coherence and teleology in performing an abductive inference in diagnostics as well as to the dual criterion of its truthfulness based both on coherence and correspondence. Examples from various medical fields are offered to illustrate the validity of the above logical claims in clinical practice.

Keywords: clinical reasoning, the ampliative leap, clinical diagnosis, logical inferences in diagnostics