in no way define it. She stated that even though the self was indefinable, it was "a totality, one of many characters... a unique being in the sense that I am I and you are you ..." In a time when there were several schools of thought, Calkins established the school of self-psychology. This became quite unpopular and controversial as many psychologists did not feel the self or soul was relevant. At the time, the main schools of psychology were structuralism and functionalism, which were quite competitive with one another; statements made by one school could expect a strong rebuttal from the other. Self-psychology was influenced by William James' theory of the idea of multiple selves (including the material self, social self, and spiritual self), and a particular interest to Calkin's, Josiah Royce's theory that humans define themselves through interpersonal communication. She spent a great deal of time working with the system of self-psychology, critically examining the self from both philosophical and psychological viewpoints. Over her many years of study, Calkins wrote many books and articles on the topic of self-psychology. Over the years she spent working on the system, it was widely unpopular, which is why she is less often remembered for her work relating to it. Despite its lack of appreciation, Calkin's refused to lose interest in the subject, which is described as "the science of conscious selves." By way of studying self-psychology, she was able to form descriptions of the self, such as the self that remains the same, the self that is changed, the unique self, and a few other descriptions. She would go on to discuss self-psychology during the entirety of her career, mentioning it in some of her books, one of which is A First Book in Psychology. Her reasoning for self-psychology being so unpopular was a notion that "one is so constantly aware of one's self that one might understandably overlook it when reporting on a sensational experience," and adding that it led to a lack of reference to the self in introspective studies. She also suggested that the system was not well taken by fellow psychologists or scientists, one of which being confusion over the self's relationship with the soul, which she discusses in her article, "The Case of Self Against Soul" in 1917. In this article, she explains that our soul should be considered life itself. She would take to theoretical