It is easy to find things that
are hidden if the hiding place is pointed out and
marked; similarly if we wish to track down some
argument we ought to know the places or topics:
for that is the name given by Aristotle to the
"regions", as it were, from which
arguments are drawn. Accordingly, we may define a
topic as the region of an argument, and an
argument as a course of reasoning which firmly
establishes a matter about which there is some
doubt.