Institutio Oratoria

If we advise, warn, promise or console, it will be grave and dignified, modest if we express fear or shame, bold in exhortation, precise in argument, full of modulations, suggestive of tears and designedly muffled in appeals for pity, whereas in digression it will be full and flowing, and will have all the resonance that is characteristic of confidence; in exposition of facts or conversations it will be even and pitched half-way betwixt high and low.

But it will be raised to express violent emotion, and sink when our words are of a calmer nature, rising and falling according to the demands of its theme. However, for the moment I will defer speaking of the variations in tone required by different topics, and will proceed first to the discussion of gesture which conforms to the voice, and like it, obeys the impulse of the mind. Its importance in oratory is sufficiently clear from the fact that there are many things which it can express without the assistance of words.