As Nordenfelt in particular criticizes the definitions of the concepts disease, illness, and sickness presented by Andrew Twaddle (Twaddle, 1994a, 1973, 1979), I will take these definitions as a point of departure and cite them at some length. According to Twaddle, disease is defined in the following way: ‘‘Disease is a health problem that consists of a physiological malfunction that results in an actual or potential reduction in physical capacities and/or a reduced life expectancy’’ (Twaddle, 1994a, p. 8). Ontologically, disease is an organic phenomenon (physiological events) independent of subjective experience and social conventions. Epistemically, it is measurable by objective means (Twaddle, 1994a, p. 9). Illness, on the other hand, is defined as follows: ‘‘Illness is a subjectively interpreted undesirable state of health. It consists of subjective feeling states (e.g., pain, weakness), perceptions of the adequacy of their bodily functioning, and/or feelings of competence’’ (Twaddle, 1994a, p. 10). Ontologically illness, then, is the subjective feeling state of the individual often referred to as symptoms. Epistemically this can only be directly observed by the subject and indirectly accessed through the individual’s reports. Sickness is defined in the following way: ‘‘Sickness is a social identity. It is the poor health or the health problem(s) of an individual defined by others with reference to the social activity of that individual’’ (Twaddle, 1994a, p. 11). Sickness in this sense is a social phenomenon constituting a new set of rights and duties. Ontologically Twaddle conceives of sickness as ‘‘an event located in society . . . defined by participation in the social system’’ (1994a, p. 11). Epistemically, sickness is accessed by ‘‘measuring levels of performance with reference to expected social activities when these levels fail to meet social standards . . .’’ (1994a, p. 11). Furthermore, Twaddle outlines the temporal relationship between disease, illness, and sickness. The paradigm case is when a disease leads to illness, which then results in sickness. Moreover, he gives a relational analysis of the triad in the form of partly overlapping spheres. This relation between the concepts of the triad will be applied in the following analysis.
III. DEFICIENCIES IN TWADDLE’S TRIAD
The conclusion of Nordenfelt’s critical analysis of Twaddle’s triad is that it is inadequate to define and describe the condition of ‘‘un-health’’. Only in the framework of a general theory of health based on a concept of disability can the triad be fruitful (Nordenfelt, 1987, pp. 105–117; 1994, p. 22, 35). Nordenfelt’s critique of Twaddle’s triad can be grouped in three areas of concern, disease, illness, and sickness respectively.