Ernst Brücke was one of the most influential figures in Sigmund Freud’s life and his work. Freud studied under him around six years during his student years and he never turned his back to Brücke’s fundamental teachings. Brücke was a member of a strictly materialist and reductionist movement called the School of Helmholtz. This school gave impetus for modern psychologist such as Wundt and Pavlov, also. In this article, we will interpret how this physiological movement influenced a psychological theory and how their teachings and understanding of science embedded to psychoanalysis. For this purpose, we will focus on the relationship between Brücke and Freud and we will demonstrate where are these influences appears in Freud’s psychoanalytical theory. Despite the common practice of evaluating Project for a Scientific Psychology as a last attempt of Freud’s physiological side, we will take Freud’s ontology and epistemology as a product of his interaction with Ernst Brücke. For this purpose, we will apply the methodology of Randall Collins, the so-called sociology of philosophy. This method will allow us to analyze personal contacts between master and pupil and the results of this interaction.