Institutio Oratoria

For just as doctors have to do more than treat the ailments which meet the eye, and need also to discover those which he hid, since their patients often conceal the truth, so the advocate must look out for more points than his client discloses to him. After he considers that he has given a sufficiently patient hearing to the latter's statements, he must assume another character and adopt the rôle of his opponent, urging every conceivable objection that a discussion of the kind which we are considering may permit.