Brentano clearly asserts, in his Vienna lectures of 1887–1888, that his descriptive psychology is an a priori or “exact” science. Since he rejects Kant's idea of a synthetic a priori, this means that the descriptive psychologist's laws are analytic. My aim in this paper is to clarify and discuss this view. I examine Brentano's epistemology in the Psychology from an Empirical Standpoint and then its later developments. I conclude with a difficulty inherent in Brentano's psychological approach to a priori knowledge.