Straddling the natural sciences in its use of observational method and the humanities through its object of study, psychoanalysis is concerned with types of evidence that are beyond the scope of philosophical cogitation. Not surprisingly, most philosophers have not welcomed the newcomer’s implicit challenge to cherished methodological and conceptual premises. Freud sketches the impact of his young discipline on philosophy in a short seminal paper, ‘A diffi culty in the path of psycho-analysis’ (1917b), while Bion (1962) traces a complex philosophical history for issues of mental growth. Drawing a distinction between the Aristotelian and the Galilean conceptions of science strikes me as a prerequisite for any understanding of the way in which philosophers and scientists view psychoanalysis.