Institutio Oratoria

But eloquence cannot be confined even to these three forms of style. For just as the third style is intermediate between the grand and the plain style, so each of these three are separated by interspaces

For there are styles fuller or plainer than the plain, and gentler or more vehement than the vehement, while the gentler style itself may either rise to greater force or sink to milder tones. Thus we may discover almost countless species of styles, each differing from the other by some fine shade of difference. We may draw a parallel from the winds. It is generally accepted that there are four blowing from the four quarters of the globe, but we find there are also a large number of winds which he between these, called by a variety of names, and in certain cases confined to certain districts and river valleys.