From Old Norse byrja (“to begin”), from Proto-Germanic *burjaną (“to lift”). Doublet of børje. The Old Norse verb is also construed with an infinitive subject in the sense "it is proper". In Modern Danish and Swedish, the verb has a personal subject and an infinitive as the object. The original Danish infinitive børe (cf. also Swedish böra) has been replaced by the past tense form burde analogically after the modal verbs kunne and skulle.