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.
Applied psychology
The founder of applied psychology was Hugo Münsterberg. He came to America (Harvard) from Germany (Berlin, Laboratory of Stern), invited by William James, and, like many aspiring psychologists during the late 19th century, originally studied philosophy. Münsterberg had many interests in the field of psychology such as purposive psychology, social psychology and forensic psychology. In 1907 he wrote several magazine articles concerning legal aspects of testimony, confessions and courtroom procedures, which eventually developed into his book, "On the Witness Stand". The following year the Division of Applied Psychology was adjoined to the Harvard Psychological Laboratory. Within 9 years he had contributed eight books in English, applying psychology to education, industrial efficiency, business and teaching. Eventually Hugo Münsterberg and his contributions would define him as the creator of applied psychology. In 1920, the International Association of Applied Psychology (IAAP) was founded, as the first international scholarly society within the field of psychology.