H. P. Grice on the ratio essendi, the ratio cognosendi, the ratio fiendi and the ratio volendi

It is known that Schopenhauer opposed Hegel and Idealism and his first fight against it was with his degree thesis On the Fourfold Root of the Principle of Sufficient Reason: very briefly, he thought that explaining a phenomenon meant relating it to something else therefore when we relate it to a principle of sufficient reason.  The first principle is the “ratio essendi”, therefore what makes something what it is: for instance the ratio essendi of a triangle is 3 sides, 3 angles with a internal sum of angles of 180 degrees and so on. This principle is used for mathematics.  The second principle is the “ratio cognoscendi” which has to do with the relation reason-consequence, applicable to logic: “if it rains therefore the floor is wet”.  The third principle is the “ratio fiendi”, the causes, therefore why something happens: this is applicable to natural sciences like physics.  The fourth and last principle is the “ratio volendi” and has to do with psychology which associates motivation-behaviour and justifies a certain individual behaviour of someone.