4. What then is this dialectics, knowledge of which must be added
to mathematics? It is a science which makes us capable of reasoning
about each thing, to say what it is, in what it differs from the
others, in what it resembles them, where it is, whether it be one of
the beings, to determine how many veritable beings there are, and
which are the objects that contain nonentity instead of veritable
essence. This science treats also of good and evil; of everything that
is subordinated to (being), the Good, and to its contrary; of the
nature of what is eternal, and transitory. It treats of each matter
scientifically, and not according to mere opinion. Instead of wandering
around the sense-world, it establishes itself in the intelligible
world; it concentrates its whole attention on this world, and after
having saved our soul from deceit, dialectics "pastures our soul in the
meadow of truth,"[347] (as thought Plato). Then it makes use of the
Platonic method of division to discern ideas, to define each object,
to rise to the several kinds of essences[348] (as thought Plato);
then, by thought concatenating all that is thence derived, dialectics
continues its deductions until it has gone through the whole domain
of the intelligible. Then, by reversing, dialectics returns to the
very Principle from which first it had started out.[349] Resting
there, because it is only in the intelligible world that it can find
rest, no longer needing to busy itself with a multitude of objects,
because it has arrived at unity, dialectics considers its logic, which
treats of propositions and arguments. This logic is an art subordinate
to dialectics just as writing is subordinate to thought. In logic,
dialectics recognizes some principles as necessary, and others as
constituting preparatory exercises. Then, along with everything else,
subjecting these principles to its criticism, it declares some of them
useful, and others superfluous, or merely technical.