The scope that theoretical psychology covers is vast. Professionals have the opportunity to use this method of seeking out theoretical knowledge to begin research in a variety of subjects. This allows for a great deal of knowledge to be explored by means of inference rather than seeking out tangible data to draw ideas. Theoretical psychology is an interdisciplinary field involving psychologists specializing in cognitive psychology, social psychology, developmental psychology, personality psychology, clinical psychology, perceptual psychology, neuropsychology, biological psychology, evolutionary psychology, historical psychology, economic psychology, political psychology, and critical psychology. It is important to acknowledge these fields do not discount empiricism, but rather explore new ideas with a theoretical approach first. Pioneers A brief history into the field of theoretical psychology includes some prominent pioneers. To begin, Wilhelm Wundt (1874) originally worked as a professor of philosophy. His focus was on the subjective study of an individual's consciousness, he believed that this was a key factor to the field of psychology. This aspect of psychology was unable to be shown with a large amount of empirical evidence, but remained a theory throughout the history of Psychology. Next, William James (1890) worked as a psychologist and a philosopher. His career focused around the idea of free will, which is theoretical in nature. He also assisted in forming the James-Lange theory of emotion, which is based upon many theoretical factors. Sigmund Freud (1905) was also an important pioneer for theoretical psychology. Freud founded the psychoanalytic theory of psychology. He did not rely on empirical data when making his theories, but instead looked for philosophical explanations. Freud often shared his view that he did not need empirical evidence for his theory, because he simply knew it is true. Another pioneer was John B. Watson (1913). Watson founded the theory of behaviorism in psychology through the article "Psychology as a Behaviorist Views It". Although Behaviorism has a strong emphasis on empirical psychology, forming the methods cannot be empirically tested, and is therefore considered theoretical psychology. Notable contributors There are some notable individuals that have, and continue to make a large impact on theoretical psychology. Jerome Kagan's (1971) work on personality traits and aging, emotion, and temperament could be considered theoretical psychology due to Kagen dedicating much of his work to psychology constructs, specifically to the developmental psychology. As a science gains new empirical procedures it also generates new information. Donald Meichenbaum (1977) had work that