Greek or Latin?

If I were asked which, of the Greek and Latin languages, is to be preferred, I would answer neither; my opinion is that they both should be used: Greek for anything that Latin cannot express, or would not offer equivalent expression for, or one less exacting; I would have Greek serve only to fill in the gaps in Latin, and this simply because familiarity with Latin is more widespread: for I concede that if we were to choose on the grounds of richness and abundance, there would be no hesitation. The Greek tongue is infinitely more extensive and expressive than Latin; it has a plethora of terms which bear the evident imprint of onomatopoeia: countless notions which have signs in that tongue have none in Latin, because it appears the Latins did not rise to any level of speculation. The Greeks had burrowed into all the depths of metaphysics of the sciences, the fine arts, logic, and grammar. With their idiom anything can be said; they have all the abstract terms relative to the operations of the understanding: witness Aristotle, Plato, Sextus Empiricus, Apollonius, and all those who wrote on grammar and rhetoric. In Latin one is often hindered by the lack of expressions: it would have taken the Romans several more centuries to integrate abstractions into their language, at least to judge by the progress they made while still under the discipline the Greeks; for in any case a single man of genius can cause ferment among a whole people, abbreviate the centuries of ignorance, and carry knowledge to a point of perfection with a surprising rapidity. But this observation does not efface the truth I am advancing: for if we count the men of genius, and distribute them over the entire span of centuries past, it is evident that there will be few of them in each nation for each century, and that almost none will be found who has not improved the language. Creative men bear this distinctive trait. Since it is not merely by leafing through the writings of their contemporaries that they find the ideas they need to use in their own writings, but sometimes rather by delving deep into themselves, at other times by bursting outside themselves, and studying more attentively and more profoundly the natures about them, they are obliged, especially at the origin of languages, to invent signs to represent exactly and forcefully what they are the first to discover. It is the fire of the imagination and deep contemplation that enrich a language with new expressions; it is keenness of mind and the severity of dialectic that perfects its syntax; it is the flexibility of the speech organs that makes it more supple; it is the ear's sensitivity that makes it harmonious.

Diderot discusses the advantages and disadvantages of using each of these classical languages.