  Since logic, viewed as the universal instrument for distinguishing between the true and the false, differs according to the objects to which it is applied and the ends for which it is used, its nature depends on the realm of possible objects and ends. Rhetoric and poetics are special cases because they deal not with knowledge but with the political disciplines in so far as they are concerned with the good of the people. Sophistical syllogistic is another special case, because it is directed towards deception and prefers to use falsehood as its material. Dialectic and demonstration, however, are directed towards the expression of truth. Dialectic is aimed at the production of opinion, and deals with probable and contingent material; demonstration is dedicated to the acquisition of truth, and so it is exclusively occupied with necessary, true objects (Kessler 1998, p. 837).