Potentiality refers to an idea sufficiently well known both in physiology and psychology. Thus, in physiology, a serous empty sac is a potential cavity; and, as respects potentiality, in reference to mental phenomena we may conveniently conceive it as parallel to the potentiality of the phenomena of life existing in the germ at the moment of its first detachment from the parent, previous to the commencement of uterine life.