Rene Descartes is an outstanding mathematician, physicist and physiologist. To this day, we use the mathematical symbolism he created, and his coordinate system reflects the intuitive idea of modern man about infinite space. But first of all, Descartes is a philosopher who proposed the method of radical doubt to solve the question of knowing the world. In "Rules for the Direction of the Mind" he attempts to prove that the result of any scientific endeavor is a particular direction of the mind, and indicates the way to achieve true knowledge. In the treatise “Principles of Philosophy,” Descartes tries to comprehend knowledge as such, questioning everything, and formulate the laws of physics. The texts are provided with detailed comments and explanations. The publishing layout of the book is saved in PDF A4 format.