Definition

Abstract

Names of diseases appear, at first sight, to refer to agents causing illness; but analysis of the ways in which they are used in medical discourse shows that they have several different sorts of factual implication. Thus the medical concept ‘a disease’ is logically heterogeneous, though this is not generally recognized (Scadding, 1959, 1963, 1972, 1981b; Campbell et al., 1979). Historically, this heterogeneity has arisen because the characteristics by which individual diseases have been defined have in many instances been changed, explicitly or implicitly, with advances in knowledge. At first, diseases could be characterized only by a distinctive combination of symptoms and signs, and thus were definable only in clinical-descriptive or syndromal terms. If a disease so defined were found to be associated with a specifiable disorder of structure or function, it tended to be redefined in terms of this new knowledge, sometimes with a new name. And when a cause of disease has been identified, causation generally displaces all other criteria as the basis of definition. Consequently, current nosology includes diseases defined in several different ways: by clinical description, by specified disorders of structure or of function, and by cause.