Institutio Oratoria

Sometimes we shall even have to hoodwink the judge and work upon him by various artifices so that he may think that our aim is other than what it really is. For there are cases when a proposition may be somewhat startling: if the judge foresees this, he will shrink from it in advance, like a patient who catches sight of the surgeon's knife before the operation. On the other hand, if we have given him no preliminary notice and our words take him unawares, without his interest in them having been previously roused by any warning, we shall gain a credence which we should not have secured had we stated that we were going to raise the point.