Zeno, a third-century B.C. Greek, cited five qualities of good (more or less formal) speech and writing:
* Language faultless in grammar and free from “careless” vulgarity
* Lucidity – presenting thought so it’s easily understood
* Conciseness – using no more words than necessary
* Appropriateness – using a style akin to the subject
* At least semi-formality, avoiding colloquialism.
As “vices of style” he cited barbarism, violation of good usage (of Greeks of good standing), and solecism, which produces “incongruous” construction. In other words, follow rules and respect tradition.
Note: He was a Stoic, which might explain some of this. Founder of Stoics, in fact. Took life as it comes, knowing better than to get over-excited.