Descartes begins the chapter affirming that the common sense is the same for all. In other words, the reason is naturally
the same for all. The multiplicity of the thought is due to the fact of the choice of the method and of the things that are taken into account. Like Descartes says, it is not enough to have a good spirit, but to have a good method. What differentiates the man of the animals is only the reason. The application of the method allows the gradual increase of the public knowledge. Discartes, the existence must be put to the test and to the judgement of the public opinion. It is convenient tthat all the sciences are examined to know his right value and truth. It is necessary still to know other cultures better to judge the culture in which one lives. Descartes, still of great importance and is able to communicate the discoveries and inventions. The French philosopher remembers still what; when it becomes attached to the custom the reason is neglected. Descartes concludes ; for the study of the method, it left the books and the customs to leave from the person interior.