Career
He was also an ordained Canon in the Catholic clergy. Falc'hun was professor at the Universities of Rennes and Brest. Contrary to the mainstream opinion of linguists, Falc'hun took the view that Breton was derived from the Gaulish form of Continental Celtic, and not from the Brythonic Celtic introduced by British migrants.
He was accused of using linguistics to promote a French nationalist political agenda. Falc'hun's early work included an edition of the writings of Jean-Marie Perrot. He created a particular Breton orthography (known as "university" orthography) which was intended to replace the spelling system known as "Peurunvan", used from 1911 to 1941.
His spelling, which does not use "zh", also abandons the Breton "c'h" convention, introduced in the seventeenth century, and which is even used in the official French form of Falc'hun's own name. In 1951 Falc'hun developed his view that Breton developed from native Gaulish, arguing that the incoming Britons encountered a Gaulish-speaking rather than Latin-speaking population, and that the two variants of Celtic merged. Criticising the views of Joseph Loth and Léon Fleuriot, Falc'hun claimed that the Vannetais dialect of eastern Breton was almost wholly Gaulish.
"I am convinced that the dialect of Vannes, especially in southern Blavet, is a Gallic survival, little influenced by British contributions, and other dialects are simply Gaulish marked by the language of origin of the island immigrants". Falc'hun's views became controversial after the publication of his 1981 book, Perspectives nouvelles sur l’histoire de la langue bretonne (New Perspectives on the History of the Breton Language), in which his theories were linked to nationalist ideology. Because of this, Falc'hun became a hate figure among Breton nationalists.
Léon Fleuriot has accepted Falc'hun's view that Breton was influenced by surviving local forms of Celtic, but rejects Falc'hun's argument that Vannetais is native Gaulish.