The human soul is declared to be simple. If it be simple, then all human faculties have the same nature.

If all human faculties have the same nature, the intellectual faculties have the same nature as, for instance, the motive faculties.

If this be so, the other faculties vary in the same way as the intellectual; and it is as idiotic to hold that a man can be good or bad, at will, or that he can be clever or stupid, a genius or an idiot at pleasure.