The criticism of the illumination theory of Henry of Ghent can be seen as the basis of the epistemology of John Duns Scotus. From this criticism it follows, that the human reason can come to an unquestionable and necessary truth without the God’s influence, as it is with the first principles, the knowledge from experience and the knowledge of the inner acts of the soul. As for the first principles, Scotus says, that their unquestionability and evidence are based on semantic compatibility of the terms, which are constitutive of these principles. In the second sphere, made of the knowledge from experience, Scotus explains his theory of induction. The necessary knowledge can be deduced from observation, by elimination of causes and by the determination of unambiguous cause of the observed phenomenon. Scotus sees the third field of the true knowledge, i. e. the inner acts of the soul, as necessary true and evident on the basis of intuitive knowledge. Scotus’ criticism of the illumination theory shows his confidence in the power of human reason as well as his optimism regarding the possibility to reach true knowledge in natural way.