A considerable part of man’s waking life is devoted to recollection of things past. Individuals, as is well known from psychotherapeutic encounters, differ in the vividness with which they envision past experiences, in the range of their reminiscences, and in the relative frequency of the recurrence of various images or themes. In the “eidetic” there is the phenomenon of total recall of specific stimuli; in the agitated depression is often seen persistent recall of an event, a derived theme, or a referring symbol. In obsessions there occur the inability to forget, the repeated representation in consciousness of a phrase, an idea, an impulse. Accompanying these memories are varying degrees of affect, measurable along various continua of intensity, pleasure, or displeasure, or of appropriateness. Occasionally one’s feelings about past events are so powerful that there develops an urge to recreate the event, to