The paper discusses the linguistic history of Cornwall and the shift from the Brittonic language to English. It highlights the contrast between Cornwall and the rest of England, where the Brittonic language continued to be spoken for nearly a thousand years after the Anglo-Saxon conquest. The subjection of Cornwall to the Anglo-Saxon kingdom of Wessex occurred in the ninth and tenth centuries, with Athelstan's expulsion of the Cornish from Exeter and the fixing of the boundary between the Britons and English at the Tamar. The event is described as a radical solution to the British problem, potentially involving ethnic cleansing. The late conquest of Cornwall, compared to the rest of England, allowed for the preservation of a distinct Cornish identity. Archaeological evidence suggests that the Tamar River served as a long-standing boundary for this identity. The decline and extinction of the Cornish language is attributed to various factors, as noted by William Scawen in his work on the decline of the language. These factors include social, political, and cultural changes. The paper also addresses the claims of Cornish being spoken in parts of South Devon during the medieval period and the presence of a Cornish-speaking flock in Menheniot during the Reformation in the 1530s.