Why do some scholars treat Latin, Osco-Umbrian, and Venetic as separate Indo-European branches rather than one Italic subfamily?

Some scholars distinguish Latin (with Faliscan), Osco-Umbrian (with South Picene), and Venetic as independent branches of the Indo-European languages rather than a single Italic subfamily because they attribute the shared features among these groups to linguistic convergence rather than a common ancestral origin.1

This perspective suggests that the similarities observed across these languages—often referred to as the "Italic" branch—arose as speakers of these distinct idioms integrated into a shared civilization during the early 1st millennium BCE. This cultural environment, known as the Etruscan koine, facilitated the adoption of common terminology for religion, administration, and literacy, masking the underlying differences between the groups.12

Evidence for this independence includes significant lexical and grammatical differences that predate this period of contact. For instance, Latin and Osco-Umbrian speakers utilized entirely different terms for fundamental concepts like "gate," "citadel," and "walls," indicating they were not in contact when they first began building cities. Consequently, while these languages share a geographic history in Italy, their classification as a unified subfamily remains a subject of scholarly debate.213