Letters 114.13

Moreover, style has no fixed laws; it is changed by the usage of the people, never the same for any length of time. Many orators hark back to earlier epochs for their vocabulary, speaking in the language of the Twelve Tables. Gracchus, Crassus, and Curio, in their eyes, are too refined and too modern; so back to Appius and Coruncanius! Conversely, certain men, in their endeavour to maintain nothing but well-worn and common usages, fall into a humdrum style.

Seneca, Letters to Lucilius 114.13, translated by Richard Mott Gummere