Institutio Oratoria

The task of dealing with the evidence of witnesses present in court is, however, one of great difficulty, and consequently whether defending or impugning them the orator employs a twofold armoury in the shape of a set speech and examination. [*](Interrogatio includes both the examination in chief and cross-examination. ) In set speeches it is usual to begin with observations either on behalf of or against witnesses in general.

In so doing we introduce a commonplace, since one side will contend that there can be no stronger proof than that which rests on human knowledge, while the other, in order to detract from their credibility, will enumerate all the methods by which false evidence is usually given.