In achieving an impressive degree of mastery over the world about us, the growth of the natural sciences has been characterized by an ever-increasing supplementation of “private operations” (sensing, feeling, inducing, deducing) with “public” ones (control and manipulation of measurable variables). As one result, even our “private” ways of perceiving the world have changed from those of our prescientific ancestors, so that at sunset, we no longer “see” the sun sinking into the sea, but “see” it disappearing beneath the horizon. Such subtle but far-reaching changes have also occurred in our dealings with our hearts, livers, and kidneys, but in dealing with our own and other people’s behaviors, most of us are still content with mentalistic explanations, the terms of which, “private” as they are, remain undefined though they may be quantified in the sense of counting the frequency of their occurrence in one or another situation. This mentalistic orientation has characterized most attempts to describe and explain drug (including opiate) addiction and relapse no less than other forms of deviant human behavior. In consequence, the clinician has tended to accept his patient’s mentalistic interpretation of his addiction and his frequent relapses to drugs as a valid one - for who else would know better what his feelings are than the patient himself? And does not one behave in accordance with one’s feelings? To be sure, the psychoanalysts have often answered both questions in the negative, designating the patient’s verbally expressed feelings as “conscious,” and their own dissenting conscious feelings about the patient’s feelings as “unconscious” ones of the patient. This certainly represents a commendable attempt to break out of the solipsistic straitjacket which, had it been allowed to restrain Columbus, would have left us convinced that the earth is flat because we “see” it that way. Unfortunately, however, the psychoanalyst’s explanations of human behavior, including drug addiction and relapse, are also couched in mentalistic terms and hence cannot be tested for validity in the accepted manner of the natural sciences-i.e., by use of “public” operations, at least directly. Reprinted with permission from Nurcorics, edited by D.I. Wilner and G.G. Kassebaum, New York: McGraw-Hill, 1965, 85-100. Possibly for these reasons, the clinician’s interests in the problem of drug addiction and relapse have been focused on the occurrence of drug-induced “euphoria.” It has been debated whether or not morphine, heroin, and other narcotic drugs (henceforth, morphine will be used as a prototype) produce euphoria in all persons or only in atypical or deviant ones (16, 21), but few have ventured to question the decisive importance of euphoria as the main determinant of the addict’s behavior, both in his initial addiction and in his subsequent relapses- for this is also the addict’s explanation. Likewise in agreement with the addict, clinicians have generally regarded morphine-induced physical dependence merely as an unpleasant complication, serving as a deterrent rather than as a motivating factor in relapse, for who but a masochist would see any virtue in those properties of a drug that produced “the agonies of the damned”