The aim of the present work is to demonstrate that physicalism and a priori knowledge are epistemologically incompatible. The possibility of a priori knowledge on physicalism will be considered in the light of Edmund Gettier’s insight regarding knowledge. In the end, it becomes apparent that physicalism entails an unavoidable disconnect between a priori beliefs and their justificatory grounds; thus precluding the possibility of a priori knowledge. Consequently, a priori knowledge and physicalism are epistemologically incompatible.