 According to Ramus, there are always three essential aspects of every art which need to be considered: nature, principles and practice (exercitatio). It was the third element, practice, which was essential, for it was through practice that one demonstrated that the art and its principles were correct. If they were correct, the art was useful and constructed according to nature. All three elements were thus closely connected, and Ramus often presented the various arts by setting out their three main parts (as, for instance, in the Dialecticae institutiones).