René Descartes (1596-1650) is synonymous with the beginning of modern philosophy. His methodical doubt calls into question all certainties while aiming to ensure the certainty of one's own existence. Undoubtedly, Descartes' positions cannot be presented as the current state of philosophical reflection. On the other hand, one cannot avoid engaging with elements of Cartesian argumentation. In addition to methodical doubt and epistemology, these include innate ideas and the mind-body dualism. Prechtl reconstructs the doubt of knowledge in a clear and comprehensible manner.