During recent years, the neurosciences have entered into a dialogue with psychoanalysis, which has opened new perspectives for their integration. Despite these developments, reservations remain concerning the reducing effects of the neurosciences by overtly or covertly hiding the core elements of psychoanalysis. However, Freud made an explicit parallel between psychoanalysis and physics in their relationship with the unknown reality, and in their task of filling in gaps in knowledge. Freud's epistemological view implies that the relationship with the unknown reality unites rather than separates psychoanalysis from other sciences. On the other hand, in the clinical realm, Freud emphasized the autonomy of psychoanalysis. Instead of offering causal explanations, the value of the neurosciences to psychoanalysis depends on how well the knowledge derived from them can be integrated in psychoanalysis and given a clinical meaning. The primacy of clinical relevance also pertains to the findings of empirical outcome research.