Institutio Oratoria

If, however, we test such corrupt eloquence by the touchstone of a critical taste, as, for example, we test inferior dyes with sulphur, it will lay aside the false brilliance that deceived the eye and fade to a pallor almost too repulsive to describe. Such passages shine only in the absence of the sunlight, just as certain tiny insects seem transformed in the darkness to little flames of fire. Finally, while many approve of things that are bad, no one disapproves of that which is good.