Every theory of love, from Plato down, teaches that each individual loves in the other sex what he lacks in himself.

Hall is best remembered for his contributions to psychology for his support of applied psychology and his success in advising many doctoral students who have made great contributions to psychology. Darwin's theory of evolution and Ernst Haeckel's recapitulation theory were large influences on Hall's career. Hall also coined the technical words describing types of tickling: knismesis or feather-like tickling; and gargalesis for the harder laughter inducing type.

Granville Stanley Hall (February 1 1844 – April 24 1924) was a pioneering American psychologist and educator. Hall was the first president of the American Psychological Association and the first president of Clark University.