* Evolution, not a sudden appearance: Languages evolve over time. Bulgarian is descended from Old Church Slavonic, which was a liturgical language used by the Slavic Orthodox Church.
* Early records: While Old Church Slavonic is attested from the 9th century, its evolution into the ancestor of modern Bulgarian began gradually.
* Modern Bulgarian: The modern Bulgarian language, with its distinctive features and literary tradition, developed over centuries. Some scholars place its emergence around the 11th-12th centuries.
Therefore, it's more accurate to say that Bulgarian has been evolving for over a millennium, rather than having a definitive "start" date.