[lucifer]

It is a disservice to Plato to assume he lacks the ability to make a distinction between a (written) correspondence and text.

Plato's statement here is likely more subtle than superficially apparent. Specifically, note that he refers comparatively to painting, which (certainly in his day) required a subject (whether mental or natural).

"[W]riting shares a strange feature with painting", in that dimensions are collapsed; the subject is 'framed'; and viewer perspective (e.g. "if anyone asks them anything") is rendered irrelevant and "continues to signify just that very same thing forever".