 Wundt (1888) agrees with Comte and Brentano that observation necessarily involves attention and so often interferes with the process to be observed, if that process is an inner, psychological one. To a much greater extent than Brentano, however, Wundt emphasizes the importance to scientific psychology of direct attention to experience, including planful and controlled variation. The psychological method of “inner perception” is, for Wundt, the method of holding and attentively manipulating a memory image or reproduction of a past psychological process. Although Wundt sees some value in this retrospective method, he thinks it has two crucial shortcomings: First, one can only work with what one remembers of the process in question—the manipulation of a memory-image cannot discover new elements. And second, foreign elements may be unintentionally introduced through association—one might confuse one’s memory of a process with one’s memory of another associated process or object.