Institutio Oratoria

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.