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.
Psychology
Psychology was a popular topic in Enlightenment Europe. In Germany, Gottfried Wilhelm Leibniz (1646–1716) applied his principles of calculus to the mind, arguing that mental activity took place on an indivisible continuum—most notably, that among an infinity of human perceptions and desires, the difference between conscious and unconscious awareness is only a matter of degree. Christian Wolff identified psychology as its own science, writing "Psychologia empirica" in 1732 and "Psychologia rationalis" in 1734. This notion advanced further under Immanuel Kant, who established the idea of anthropology, with psychology as an important subdivision. However, Kant explicitly and notoriously rejected the idea of experimental psychology, writing that "the empirical doctrine of the soul can also never approach chemistry even as a systematic art of analysis or experimental doctrine, for in it the manifold of inner observation can be separated only by mere division in thought, and cannot then be held separate and recombined at will (but still less does another thinking subject suffer himself to be experimented upon to suit our purpose), and even observation by itself already changes and displaces the state of the observed object." Having consulted philosophers Hegel and Herbart, in 1825 the Prussian state established psychology as a mandatory discipline in its rapidly expanding and highly influential educational system. However, this discipline did not yet embrace experimentation. In England, early psychology involved phrenology and the response to social problems including alcoholism, violence, and the country's well-populated mental asylums.