In 1897, Külpe published a handbook called Introduction to Philosophy. This book was a guide to both past and present philosophy at the time, and a basic text for German university students of not just general philosophy, but psychology, logic, ethics, and aesthetics as well. In the book, Külpe also looks at the relations of the body and the mind, and in doing so, takes a dualistic position. Külpe also gives a clearly describes the relationship between physical and psychical, or in other words natural science and psychology. He identifies the possibility of what he refers to as a mind substance. He theorized that both matter and mind are abstractions from thought experience. He believed that if matter required the idea of substance, why would mind not require substance as well. The book is less than 350 pages and went through seven editions and four translations, including into English by W.B. Pillsbury and Titchener under the title Introduction to Philosophy.