Gustav Fechner
Fechner, along with Wilhelm Wundt and Hermann von Helmholtz, is recognized as one of the founders of modern experimental psychology. His clearest contribution was the demonstration that because the mind was susceptible to measurement and mathematical treatment, psychology had the potential to become a quantified science. Theorists such as Immanuel Kant had long stated that this was impossible, and that therefore, a science of psychology was also impossible.
John Dewey
In 1984, the American Psychological Association announced that Lillian Moller Gilbreth (1878–1972) had become the first psychologist to be commemorated on a United States postage stamp. However, psychologists Gary Brucato Jr. and John D. Hogan later made the case that this distinction actually belonged to John Dewey, who had been celebrated on an American stamp 17 years earlier. While some psychology historians consider Dewey more of a philosopher than a bona fide psychologist, the authors noted that Dewey was a founding member of the A.P.A., served as the A.P.A.'s eighth president in 1899, and was the author of an 1896 article on the reflex arc which is now considered a basis of American functional psychology.