Institutio Oratoria

Still, even in the case of witnesses whose evidence is consistent, we must be on our guard against treachery. For such witnesses are often put up by one's opponent and, after promising to say everything that will help our case, give answers of exactly the opposite character and carry more weight by the admission of facts which tell against us than they would have done had they disproved them.

We must therefore discover what motives they have for doing our opponent a hurt, and the fact that they were once his enemies will not suffice our purpose: we must find out whether they have ceased to be ill-disposed to him or whether they desire by means of their evidence to effect a reconciliation with him, in order to assure ourselves that they have not been bribed or repented of

For experience shows that they are more likely to repent of their purpose, their promises are less to be relied on, and, if they do keep their promise, their evidence is easier to refute.

Witnesses appearing in answer to a subpoena may be divided into two classes: those who desire to harm the accused, and those who do not. The accuser sometimes is aware of their disposition, sometimes unaware. For the moment let us assume that he is aware of their disposition, although I must point out that in either case the utmost skill is required in their examination.

For if an advocate is producing a witness who is desirous of harming the accused, he must avoid letting this desire become apparent, and must not at once proceed to question him on the point at issue. On the contrary this point must be approached by a circuitous route in such a manner as to make it seem that the statement which the witness is really desirous of making has been forced from him. Again lie should not press the witness too much, for fear he should impair his credit by the glibness with which lie answers every question, but should draw from him just so much as may seem reasonable to elicit from a single witness.