foster states that “human beings of sufficient maturity have minds. . . . and some will accept the existence of non-embodied minds, such as those of God, angels, and departed spirits. . . . mentality is not reducible to something else. . . . the mental and the physical realms are ontologically separate. roughly, what this means is that the entities which feature in the one realm are entirely different from those which feature in the other - that the class of mental-realm entities and the class of physical-realm entities do not overlap.”