Institutio Oratoria

Consequently, all I can do is now and hereafter to show what should be done or avoided in each particular case, with a view thereby to guide the judgment. What use then is it for me to lay down general rules to the effect that we should not attempt impossibilities, that we should avoid whatever contradicts our case or is common to both, and shun all incorrectness or obscurity of style? In all these cases it is common sense that must decide, and common sense cannot be taught.