Can psychiatric disorders be conceptualized as "harmful dysfunctions" (J. C. Wakefield, 1992a, 1992b, 1999; S. O. Lilienfeld & L. Marino, 1995)? Wakefield's (1992a) central concept of disorder as "harmful dysfunction" is discussed by placing it in the context of a complementary discussion of disease, illness, the sick role, and evolution (D. F. Klein, 1978). S. O. Lilienfeld and L. Marino (1995) contended that proper biological function cannot be determined. This argument obscures the key significance of involuntary impairment of evolved functions. The claim that the Roschian concept has no counterpart in reality is incorrect and does not support the conclusion that dysfunctions are irreducibly evaluative and therefore arbitrary. J. C. Wakefield's (1999) views in this area are supplemented. The role of monothetic and polythetic categorization, extremal terms, and the concept of normality in nosology is considered. This analysis refutes the implication that deviance and illness are equivalent. The resolution of this debate is practically relevant to emphasizing areas of research investment, such as therapeutics.