Hermann Ebbinghaus

"The constant flux and caprice of mental events do not admit of the establishment of stable experimental conditions."

"What is true is alas not new, the new not true."

"Ideas 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."

"Natural science served as - if we overlook the hasty identification of mind and matter which had its origin in natural science - as a shining and fruitful example to psychology."

"The foreseeing of our attention is the will to give attention, is voluntary attention."

"Mental events, it is said, are not passive happenings but the acts of a subject."

"No 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. But if he chances to set out purposely to learn it backwards, he will probably accomplish this in noticeably shorter time than was the case in the previous learning in the customary order."

"Psychology has a long past, yet its real history is short. For thousands of years it has existed and has been growing older ; but in the earlier part of this period it cannot boast of any continuous progress toward a riper and richer development. In the fourth century before our era that giant thinker, Aristotle, built it up into an edifice comparing very favorably with any other science of that time. But this edifice stood without undergoing any noteworthy changes or extensions, well into the eighteenth or even the nineteenth century. Only in recent times do we find an advance, at first slow but later increasing in rapidity, in the development of psychology."

"Popular thought, supported by desires common to all human beings, readily accepts the view that mind is essentially different from matter, that its laws are in every respect different from the laws of material nature, and that the brain, being a part of the material nature, is simply the special tool used by the mind in its intercourse with nature."

"Language is a system of conventional signs that can be voluntarily produced at any time."

"Mental states of every kind — sensations, feelings, images— which were at one time present in consciousness and then have disappeared from it — have not with their disappearance absolutely ceased to exist. Although the inwardly - turned look may no longer be able to find them, nevertheless they have not been utterly destroyed and annulled, but in a certain manner they, continue to exist, stored up to speak, in the memory."

"A poem is learned by heart and then not again repeated. We will suppose that after a half year it has been forgotten: no effort of recollection is able to call it back again into consciousness."