It is, however, the evidence that gives the greatest trouble to advocates. Evidence may be given either in writing or orally by witnesses present in court. Documentary evidence is easier to dispose of. For it is likely that the deponent was less ashamed of himself in the presence of a small number of witnesses, and his absence from court is attacked as indicating a lack of confidence. If we cannot call the character of the deponent in question, we may attack the witnesses to his signature.

Further there is always a certain tacit prejudice against documentary evidence, since no one can be forced to give such evidence save of his own free will, whereby he shows that he harbours unfriendly feelings towards the person against whom he bears witness. On the other hand an advocate should be chary of denying that a friend may give true evidence against a friend or an enemy against an enemy, provided they are persons of unimpeachable credit. But the subject admits of copious discussion, from whichever side it be regarded.

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.

The next procedure is the common practice of making a special attack, which all the same involves impugning the validity of evidence given by large numbers of persons. We know, for instance, that the evidence of entire nations e.g. in cases of extortion, where a whole province might give evidence against the accused. and whole classes of evidence have been disposed of by advocates. For example, in the case of hearsay evidence, it will be urged that those who produce such evidence are not really witnesses, but are merely reporting the words of unsworn persons, while in cases of extortion, those who swear that they paid certain sums to the accused are to be regarded not as witnesses, but as parties to the suit.

Sometimes however the advocate will direct his speech against single individuals. Such a form of attack may be found in many speeches, sometimes embedded in the speech for the defence and sometimes published separately like the speech against the evidence of Vatinius. Vatinius had appeared as a witness against Sestius, who was defended by Cicero.