In things equal to one another, in this way:—­“For as a place without a harbour cannot be safe for ships, so a mind without integrity cannot be trustworthy for a man’s friends.”  In those things which fall under the same principle a probable argument is considered in this way:—­“For if it be not discreditable to the Rhodians to let out their port dues, then it is not discreditable even to Hermacreon to rent them.”  Then these arguments are true, in this manner:—­“Since there is a scar, there has been a wound.”  Then they are probable, in in this way:—­“If there was a great deal of dust on his shoes, he must have come off a journey.”  But (in order that we may arrange this matter in certain definite divisions) every probable argument which is assumed for the purpose of discussion, is either a proof, or something credible, or something already determined; or something which may be compared with something else.

That is a proof which falls under some particular sense, and which indicates something which appears to have proceeded from it, which either existed previously, or was in the thing itself, or has ensued since, and, nevertheless, requires the evidence of testimony, and a more authoritative confirmation,—­as blood, flight, dust, paleness, and other tokens like these.  That is a credible statement which, without any witness being heard, is confirmed in the opinion of the hearer; in this way:—­There is no one who does not wish his children to be free from injury, and happy.  A case decided beforehand, is a matter approved of by the assent, or authority, or judgment of some person or persons.  It is seen in three kinds of decision;—­the religious one, the common one, the one depending on sanction.  That is a religious one, which men on their oaths have decided in accordance with the laws.  That is a common one, which all men have almost in a body approved of and adopted; in this manner:—­“That all men should rise up on the appearance of their elders; That all men should pity suppliants.”  That depends on sanction, which, as it was a doubtful point what ought to be considered its character, men have established of their own authority; as, for instance, the conduct of the father of Gracchus, whom the Roman people made consul after his censorship, because he had done nothing in his censorship without the knowledge of his colleague.

But that is a decision admitting of comparisons, which in a multitude of different circumstances contains some principle which is alike in all.  Its parts are three,—­representation, collation, example.  A Representation is a statement demonstrating some resemblance of bodies or natures; Collation is a statement comparing one thing with another, because of their likeness to one another; Example is that which confirms or invalidates a case by some authority, or by what has happened to some man, or under some especial circumstances.  Instances of these things, and descriptions of them, will be given amid the precepts for oratory.