Breton a-marking of (internal) verbal arguments: A result of language contact?

We discuss a potential case of borrowing in this paper: Breton a- ‘of’, ‘from’ marking of (internal) verbal arguments, unique in Insular Celtic languages, and reminiscent of Gallo-Romance de/du- (and en-) arguments. Looking at potential Gallo-Romance parallels of three Middle Breton constructions analyzed in some detail (a with indefinite mass nominals in direct object position, a-marking of internal arguments under the scope of negation, a [allomorphs an(ez)-/ahan-] with personal pronouns for internal arguments, subjects (mainly of predicative constructions) and as expletive subjects of existential constructions), we demonstrate that even if there are some semantic parallels and one strong structural overlap (a and de under the scope of negation), the amount of divergences in morphology, syntax and semantics and the only partially fitting relative chronology of the different constructions do not allow to conclude with certainty that language-contact is an explanation of the Breton facts, which might have come into being also because of internal change (bound to restructuring of the pronominal system in Breton). More research is necessary to complete our knowledge of a-marking in Middle Breton and Modern Breton varieties and on the precise history of French en, in order to decide for one or the other explanation