Institutio Oratoria
Quintilian
Quintilian. Institutio Oratoria, Volume 1-4. Butler, Harold Edgeworth, translator. Cambridge, Mass; London: Harvard University Press, William Heinemann Ltd., 1920-1922.
those who testify of their own free will and those who are summoned to attend in the public courts of whom the former are available to either party, the latter solely to the accusers, we must distinguish between the duties of the advocate who produces witnesses and the advocate who refutes them.
He who produces a voluntary witness is in a
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position to know what he is likely to say: consequently the task of examining him would seem to be rendered easier. But even here such cases make a great demand on the acumen and watchfulness of the advocate, who must see that his witness is neither timid, inconsistent nor imprudent.