Series of syllables which have been learned by heart, forgotten, and learned anew must be similar as to their inner conditions at the times when they can be recited.
Hermann EbbinghausIdeas which have been developed simultaneously or in immediate succession in the same mind mutually reproduce each other, and do this with greater ease in the direction of the original succession and with a certainty proportional to the frequency with which they were together
Hermann EbbinghausNo matter how thoroughly a person may have learned the Greek alphabet, he will never be in a condition to repeat it backwards without further training.
Hermann Ebbinghaus