Institutio Oratoria
Quintilian
Quintilian. Institutio Oratoria, Volume 1-4. Butler, Harold Edgeworth, translator. Cambridge, Mass; London: Harvard University Press, William Heinemann Ltd., 1920-1922.
But the thing itself has an extraordinarily powerful effect in oratory. For the nature of the speech that we have composed within our minds is not so important as the manner in which we produce it, since the emotion of each member of our audience will depend on the impression made upon his hearing. Consequently, no proof, at least if it be one devised by the orator himself, will ever be so secure as not to lose its force
For when we have done all this, we may still account ourselves only too fortunate if we have succeeded in communicating the fire of our passion to the judge: consequently, we can have no hope of moving him if we speak with languor and indifference, nor of preventing him from yielding to the narcotic influence of our own yawns.
A proof of this is given by actors in the theatre. For they add so much to the charm even of the greatest poets, that the verse moves us far more when heard than when read, while they succeed in securing a hearing even for the most worthless authors, with the result that they repeatedly win a welcome on the stage that is denied them in the library.
Now if delivery can count for so much in themes which we know to be fictitious and devoid of reality, as to arouse our anger, our tears or our anxiety, how much greater must its effect be when we actually believe what we hear? For my own part I would not hesitate to assert that a mediocre speech supported by all the power of delivery will be more impressive than the best speech unaccompanied by such power.