Wundt defined psychology as a science to be differentiated from philosophy, specifically, German idealism, spiritualism, and metaphysics. His was a "pure" discipline based on experimental methods and natural or social scientific principles. When William James imported Wundtian psychology to the United States, he expanded its theoretical reach but diluted its scientific methods. Unlike Wundt, James established it in academic departments of philosophy and tried to build a bridge between psychology and the nation’s popular obsession with spiritualists. It was left to G. Stanley Hall to create the necessary infrastructure to make psychology a legitimate academic discipline: scientific peer-reviewed journals, a scientific society (i.e., the American Psychological Association), and separate degree-granting academic departments of psychology. Hall was also the first to recognize Freud’s contribution and invited him to give the famous lectures at Clark University, where Hall was president.