Memory illusion, or paramnesia, consists in the illusory opinion of having experienced, seen, or heard something, although there has been no such experience, vision, or sound. It is the more important in criminal law because it enters unobtrusively and unnoticed into the circle of observation, and not directly by means of a demonstrated mistake. Hence, it is the more difficult to discover and has a disturbing influence which makes it very hard to perceive the mistakes that have occurred in consequence of it. It may be that Leibnitz meant paramnesia with his “perceptiones insensibiles.” Later, Lichtenberg must have had it in mind when he repeatedly asserted that he must have been in the world once before, inasmuch as many things seemed to him so familiar, although, at the time, he had not yet experienced them. Later on, Jessen concerned himself with the question, and Sander[231] asserts him to have been the first. According to Jessen, everybody is familiar with the phenomenon in which the sudden impression occurs, that what is experienced has already been met with before so that the future might be predicted. Langwieser asserts that one always has the sensation that the event occurred a long time ago, and Dr. Karl Neuhoff finds that his sensation is accompanied with unrest and contraction. The same thing is discussed by many other authors.[232] Various explanations have been offered. Wigand and Maudsley think they see in paramnesia a simultaneous functioning of both relations. Anje believes that illusory memory depends on the differentiation which sometimes occurs between perception and coming-into-consciousness. According to Külpe, these are the things that Plato interpreted in his doctrine of pre-existence. Sully,[233] in his book on illusions, has examined the problem most thoroughly and he draws simple conclusions. He finds that vivacious children often think they have experienced what is told them. This, however, is retained in the memory of the adult, who continues to think that he has actually experienced it. The same thing is true when children have intensely desired anything. Thus the child-stories given us by Rousseau, Goethe, and De Quincey, must come from the airy regions of the dream life or from waking revery, and Dickens has dealt with this dream life in “David Copperfield.” Sully adds, that we also generate illusions of memory when we assign to experiences false dates, and believe ourselves to have felt, as children, something we experienced later and merely set back into our childhood. So again, he reduces much supposed to have been heard, to things that have been read. Novels may make such an impression that what has been read or described there appears to have been really experienced. A name or region then seems to be familiar because we have read of something similar.