Theoretical psychology is concerned with theoretical and philosophical aspects of psychology. It is an interdisciplinary field with a wide scope of study. It focuses on combining and incorporating existing and developing theories of psychology non-experimentally. Theoretical psychology originated from the philosophy of science, with logic and rationality at the base of each new idea. It existed before empirical or experimental psychology. Theoretical psychology is an interdisciplinary field involving psychologists specializing in a wide variety of psychological branches. There have been a few prominent pioneers of theoretical psychology such as Wilhelm Wundt, William Jones, Sigmund Freud, and John B. Watson. There has also been a number of notable contributors which include Jerome Kagan, Alan E. Kazdin, Robert Sternberg, Kenneth J. Gergen, and Ulric Neisser. These contributors often publish in a variety of journals including the most prominent for theoretical psychology, the Journal of Theoretical and Philosophical Psychology. Many other organizations are beginning to recognize theoretical psychology as a formal subdivision of psychology.