Metaphysical dissolution takes the form of a double-aspect theory whereby some sort of transcendental reality is perceived by the subject in two distinct aspects as the mental and the physical. More specifically, some proponents of an identity hypothesis have accepted a behaviourist account of mental phenomena other than sensations. The hypothesis purports or promises to satisfy both of the criteria for a solution to the mental–physical puzzle, because it is both metaphysically conservative and true to experience in so far as it is nonreductionist with respect to phenomena. The Cartesian dualist model of persons and their behavior can be taken in toto as the root metaphysical model of the prevailing orthodoxy. The Cartesian dichotomy between mind and body as immaterial and material substances poses the problem of their relation or interaction. Reasons for considering a mind–brain identity theory have been offered, based primarily upon developments in the life sciences which support the physicalist alternative to the orthodox model.