As Adanson says, the system is like 'the trial and error method in mathematics': it is the result of a decision, but it must be absolutely coherent; the method, on the other hand, is a given arrangement of objects or facts grouped together according to certain given conventions or resemblances, which one expresses by a general notion applicable to all those objects, without, however, regarding that fundamental notion or principle as absolute or invariable, or as so general that it cannot suffer any exception. .