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.
History of psychology
Early psychology was regarded as the study of the soul (in the Christian sense of the term). The modern philosophical form of psychology was heavily influenced by the works of René Descartes (1596–1650), and the debates that he generated, of which the most relevant were the objections to his "Meditations on First Philosophy" (1641), published with the text. Also important to the later development of psychology were his "Passions of the Soul" (1649) and "Treatise on Man" (completed in 1632 but, along with the rest of "The World", withheld from publication after Descartes heard of the Catholic Church's condemnation of Galileo; it was eventually published posthumously, in 1664).