Summary: The topic here proposed can be interesting in itself for the fact that John Duns Scotus, the last great medieval theologian, came quite a while after St. Thomas Aquinas and St. Bonaventure, and knew their doctrine very well. His contribution is divided into two fundamental parts. The first regards the intrinsic particularity of the procession of the Son and that of the Holy Spirit. This vision, profoundly conformed to the teachings of St. Augustine and St. John Damascene, gives reason to the Scotist thesis as well, whereby theoretically the Holy Spirit would be distinguished from the Son, even if he should not proceed from Him. The second part refers to the constitutive principle of the divine Person. While theological solutions oscillated between the two poles, which were the absolute properties (among Greek doctors) and the opposite relations of the origin (according to the majority of the Latins, including St. Thomas), brother John assumes a conciliatory position, pronouncing himself certainly for the relations, but not considering the other opinion unacceptable. His contribution therefore contains many elements which are rooted in patristic theology, both Latin and Greek, for which reason he can be of help in dialogue with the separated Christians of the East.