The Rules for the Direction of the Mind, composed between 1628 and 1629, and published posthumously, constitute the first major philosophical text by Descartes (1596-1650). Through these rules, the author aims to explain the mode of resolution of all the questions that may arise for man, and to manifest the fundamental unity of the spirit, in a way which announces the Discourse of the method (1637). The method is presented as putting natures in order, and the main operations of the mind, intuition and deduction, are exposed. Jointly, Descartes formulates the project of mathesis universalis, this universal science which, as a general science of order and measurement, must make it possible to resolve all questions, and not only those which are mathematizable in the strict sense. So many themes which make the study of the Rules the complement of that of the Discourse on Method.