This article analyses the most fundamental aspects of the theory of knowledge presented in the course dictated in 1689 by Friar Juan de Fuica (OFM) at San Diego de Alcala College, Santiago de Chile. First, we present a brief description of the Philosophical Commentaries of the Friar, volume that includes the Commentaries On the soul on which we focus our study. Second, we analyze the ad mentem Scoti doctrine of knowledge presented in this unreleased manuscript, which is an exclusive testimony of philosophy teachings at that time. The main contribution of this paper is to turn visible a part of the colonial philosophical heritage of the country, which will make possible new research in this philosophical area.