Thanks for the info.
I will look for what Plato had to say on the subject as well.
I'm looking for an explicit quotation about this from a relatively foundational linguistic. I'm not strictly looking to track the academic history of the idea, but rather to "go to the source" for what may become an epigraph or opening citation in the text. It's about why I'm doing this, not that I'm strictly following that line of research (I do, however, agree with that much though!).