What was the main language of learning and the Church in Western Europe for much of the Middle Ages?

The story behind the answer

It was the shared scholarly and ecclesiastical language of Western Christendom. Clergy conducted liturgy and wrote theology, canon law, and philosophy in it; monasteries and cathedral schools taught it and copied manuscripts; and the first universities used it as their medium of instruction. This continuity stemmed from the Western Roman Empire’s legacy and efforts like Charlemagne’s reforms, which promoted standardized education and script.

While vernaculars such as Old English and Old French grew for everyday use, cross-regional scholarship—from England to Italy—relied on a common tongue. Greek, by contrast, was far less known in the Latin West until renewed contact and translations (often via Arabic) during the 12th-century renaissance. Even late into the Middle Ages, major works, from the Vulgate Bible to scholastic treatises by Aquinas, appeared in this language, cementing its role as the intellectual glue of Europe.