A new strategy for clinical decision making--II. The circumscription of non-monotonicity and differential diagnosis for thyroid diseases.

The physician or scientist must contend with multiple interactions in medicine. Differential diagnosis, or the determination of which of two or more diseases a patient is suffering from, arises from the complexity of these interactions. Some of these interactions can mask or inhibit the true diagnosis. These inhibiting factors are called censors. Because of censors, switching points are required in non-monotonic reasoning associated with a differential diagnosis. In order to render these censors--and non-monotonic reasoning--susceptible of computation, they must first be circumscribed. This paper examines circumscription as a form of non-monotonic reasoning augmenting first-order logic through censorship in the diagnosis of thyroid patients. This approach to circumscription is inspired by the influential work of John McCarthy at Stanford University.