To understand the role of psychology as science according Edith Stein, we have to clarify the main features of her philosophical anthropology. Through the phenomenological analysis of the lived experiences she discovers the complex structure of the human being: the bodily, the psychic, and the spiritual life. The psychic level is ruled by causality, but it is different from the causality that we find in the nature, because it is not deterministic. In the psyche there is also an implicit motivation, but the explicit one is present in the spiritual life. For this reason, according to her, psychology, even if it is the science of the psyche, cannot avoid dealing with the spiritual aspect of the human being. Stein’s position is very important in order to grasp the limits of a psychology that follows the model of natural sciences.