The paper provides a reconstruction of the notion of genetic phenomenology while trying to demonstrate that its elaboration leads Husserl to dismiss de facto the main motivation of his idealism—namely the idea that at the basis of constitution is an immanent and formless stuff shaped or animated by subjective acts. Indeed genetic analysis shows that the original stuff of constitution consists of sensuous contents structured according to a material lawfulness grounded on their peculiarity. By affecting the subject, such contents motivate the performing of intentional acts and are the genuine motor of constitution. The genetic ground of apperceptions is thus material content.