Abstract

Taking Haspelmath’s definition of the infinitive as a grammaticalized purposive used as complement predicate as a starting point, the article shows that the Old Irish construction consisting of do ‘to’ plus verbal noun with preposed subject or object fulfills these criteria. It is demonstrated that the infinitival phrase developed out of a purposive adverbial phrase that underwent desemanticization and came to be used as complement. In addition, reanalysis of an argument of the matrix clause as overt subject or object of the infinitive led to the typical shape of the do-infinitive with preposed subject or object.