which are hidden is easy,
if the place where they are hidden is pointed out and clearly marked;
so, when we wish to examine any argument, we ought to know the
topics,--for so they are called by Aristotle, being, as it were,
seats from which arguments are derived. Therefore we may give as a
definition, that a topic is the seat of an argument, and that an
argument is a reason which causes men to believe a thing which would
otherwise be doubtful. But of those topics in which arguments are
contained, some dwell on that particular point which is the subject of
discussion; some are derived from external circumstances. When derived
from the subject itself, they proceed at times from it taken as a
whole, at times from its parts, at times from some sign, and at others
from things which are disposed in some manner or other towards the
subject under discussion; but those topics are derived from external
circumstances which are at a distance and far removed from the same
subject.

But a definition is employed with reference to the entire matter under
discussion which unfolds the matter which is the subject of inquiry as
if it had been previously enveloped in mystery. The formula of that
argument is of this sort: "Civil law is equity established among men
who belong to the same city, for the purpose of insuring each man in
the possession of his property and rights: and the knowledge of this
equity is useful: therefore the knowledge of civil law is useful."
Then comes the enumeration of the parts, which is dealt with in this
manner: "If a slave has not been declared free either by the censor,
or by the praetor's rod, or by the will of his master, he is not free:
but none of those things is the case: therefore he is not free." Then
comes the sign; when some argument is derived from the meaning of a
word, in this way:--As the Aelian Sentian law orders an assiduus[63] to
support an assiduus, it orders a rich man to support a rich man, for a
rich man is an assiduus, called so, as Aelius says, from _asse dando_.

III. Arguments are also derived from things which bear some kind of
relation to that which is the object of discussion. But this kind is
distributed under many heads; for we call some connected with one
another either by nature, or by their form, or by their resemblance to
one another, or by their differences, or by their contrariety to
one another, or by adjuncts, or by their antecedents, or by their
consequents, or by what i