[2] Elocutio or style is the third of the five canons of classical rhetoric (the others being inventio, dispositio, memoria, and pronuntiatio) that concern the craft and delivery of speeches and writing.
First, there was the level of style; plain (attenuata or subtile), middle (mediocris or robusta), or high (florida or gravis).
For instance, Quintilian in his Institutio Oratoria deemed the plain style suitable for instruction, the middle for moving oration, and the high for charming discourse.
The ancient authors agreed that the four ingredients necessary to achieve good style included correctness, clearness, appropriateness, and ornament.
[5] Sometimes translated as "purity", correctness meant that rhetors should use words that were current and adhered to the grammatical rules of whatever language they wrote.