How did Romance speakers eventually recognize that their everyday speech differed from Classical Latin?

The realization that everyday speech had diverged from Classical Latin was not a sudden event but a gradual process of linguistic drift. While some scholars suggest this awareness emerged as early as the 5th century due to social disruptions, the most significant evidence for this recognition appears in the 9th century.1

This shift in consciousness was largely catalyzed by the Carolingian Renaissance, an intellectual movement led by Charlemagne. Concerned that contemporary Latin usage had fallen short of classical standards, Charlemagne and scholars like Alcuin of York sought to revive "purer" Latin for administration and the church. As this standardized, classical form of Latin was re-established, it became increasingly obvious that the vernacular spoken by the people was a distinct language.23

This distinction was formally acknowledged in 813, when the Council of Tours decreed that sermons should be delivered in rusticam Romanam linguam ("the rustic Roman language") to ensure they remained intelligible to the congregation. Thus, the effort to restore Classical Latin effectively highlighted the gap between it and the evolving vernaculars.21