This thesis, whose theme is " Reason and morality in Descartes", examines the split operated by man in the being which is in itself unique and rational. Indeed, our primary apprehension of being presents it in the form of multiplicity. Based on Cartesian rationalism, our work shows that reason is a principle of unity that exists in the world. From this point of view, natural morality is but the exemplary manifestation of this divine reason. Because of the unity that characterizes him, the educated man can be understood as one who does not separate essential values; rational activity and moral reason, operational knowledge and education, individualization and socialization. This is why education, whether it is called rationalisation or moralisation, can be thought of as a global success of man as soon as the different values are not perceived by him as dualities, but rather as ways of being of the one reason whose recurrence we have underlined in Descartes and which constitutes inhis philosophy the foundation of morality.