Institutio Oratoria

If the whole of rhetoric could be thus embodied in one compact code, it would be an easy task of little compass: but most rules are liable to be altered by the nature of the case, circumstances of time and place, and by hard necessity itself. Consequently the all-important gift for an orator is a wise adaptability since he is called upon to meet the most varied emergencies.

What if you should instruct a general, as often as he marshals his troops for battle, to draw up his front in line, advance his wings to left and right, and station his cavalry to protect his flank? This will perhaps be the best plan, if circumstances allow. But it may have to be modified owing to the nature of the ground, if, for instance, he is confronted by a mountain, if a river bars his advance, or his movements are hampered by hills, woods or broken country.

Or again it may be modified by the character of the enemy or the nature of the crisis by which he is faced. On one occasion he will fight in line, on another in column, on one he will use his auxiliary troops, on another his legionaries; while occasionally a feint of flight may win the day. So, too, with the rules of oratory.