 That thesis was later integrated into Husserl’s first published monograph, Philosophy of Arithmetic, which appeared in 1891. In this work, Husserl combined his mathematical, psychological and philosophical competencies to attempt a psychological foundation of arithmetic (see Willard 1984, pp. 38–118; Bell 1990, pp. 31–84). The book was, however, criticized for its underlying psychologism in a review by Gottlob Frege. It seems that Husserl took that criticism very seriously (see Føllesdal 1958), although it is far from clear that the author of Philosophy of Arithmetic regards logic as a branch of psychology, as “strong psychologism” (Mohanty 1982, p. 20) has it. In any case, Husserl sharply attacked that kind of psychologism (raising about eighteen objections in total; see Soldati 1994, pp. 117 ff) and developed the philosophical method he is nowadays famous for: phenomenology.