The schoolboy doesn't force himself to learn his vocabularies and rules altogether at night, but knows that he must impress them again in the morning. - Hermann Ebbinghaus

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

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.

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.