 It is notable that Poulain’s reference to the necessity of getting completely rid of prejudices follows the radical nature of Descartes’ doubt and its emphasis on rejecting everything as false, unless it is entirely indubitable. Poulain is true to Descartes’ terminology also at the end of the cited paragraph, where he refers to certain knowledge as “clear and distinct”. In Principia philosophiae (part I, § 45), Descartes emphasizes that in order to “serve as the basis for a certain and indubitable judgment” a perception needs to “be not merely clear but also distinct” (CSM I, 207; AT VIIIA, 22). By “clear” he means that “it is present and accessible to the attentive mind” and in order to be “distinct” it must, in addition to being clear, be “so sharply separated from all other perceptions that it contains within itself only what is clear” (CSM I, 208; AT VIIIA, 22).