Although Freud viewed symptoms as substitutive satisfactions for the frustrations in life, the mechanism of substitution was not explained. Symptoms are ego alien, can be displaced, and imply the existence of a drive. The search for the hidden substitute is carried out under the economic theory. Using several clinical examples, Reider indicates that the substitution may be either from one symptom to another (ego-dystonic) or from a symptom to behavior (ego-syntonic). The prototype of this kind of displacement to contiguous objects may be the infant's developmental enlargement of its visual scope from its mother's face to other objects. The earliest model of therapy may be the correction by the mother of the infant's experiences of discomfort, the neutralization of excesses or deficiencies by an authority figure. With examples of the treatment of obesity and anorexia nervosa, Reider shows how most instances of symptom substitution involve the turning of a passive phenomenon into an active one, with contiguity or symbolic representation a determinant in the new symptom.