As a canonist Hostiensis had a great reputation. His works are:
Lectura in Decretales Gregorii IX, a work begun at Paris but continued during his whole life;
Summa super titulis Decretalium, also known as Summa archiepiscopi or Summa aurea; written while he was Archbishop of Embrun, a work on Roman and canon law, which won for its author the title Monarcha juris, lumen lucidissimum Decretorum. One portion of this work, the Summa, sive tractatus de poenitentia et remissionibus was very popular. It was written between 1250 and 1261.
*
Lectura in Decretales Innocentii IV, which was never edited.
A work on feudal law has also been attributed to him, but without foundation.
Hostiensis on papal ''plenitudo potestatis''
For Hostiensis the law as well as all political authority were derived from God. Because of this all princes “exercised authority by divine mandate.” Civil law was divine because the emperors who created that law were placed in authority by God. Despite this, however, civil law was inferior to canon law. The reason for this is that the pope’s authority was even closer to the divine than that of secular princes. Because the pope was the vicar of God he acted on God’s authority, from which he derived his own authority. Thus, whenever the pope acted de iure he acted as God. Therefore, canon law, since it was promulgated by the pope, was established by God. This is because canon law was based on the bible, and God had given his vicar, the pope, the authority to interpret that text. Thus canon law was divine not because it came directly from God, but because of the end it sought and because of the dignity of the Pope, from which the canon law emanated. Hostiensis believed that while the pope should follow positive law he was not bound by it. Thus the pope could not be tried for any crime, except that of heresy, in which case “the pope could be subject to the 'ecclesia'." For any other violation of law the pope could be judged by no one save God. Further, except in the event that a mortal sin would result, the pope was to be obeyed in everything he commanded, including violations of positive law, since the pope was above that law. The only exception to this was if the pope’s command violated the conscience of the one being commanded, in which case the one being commanded should not obey. Similarly, Hostiensis believed that the pope could grant exemptions even from divine law, so long as that exemption did not lead to a mortal sin, violate the faith, subvert the faith, or endanger the salvation of souls. The pope had great authority indeed, he could even "change squares into circles. According to Hostiensis the pope was imbued with the authority of the two swords, interpreted as spiritual and temporal power. The spiritual was superior to the temporal in the following three aspects: “in dignity, for the spirit is greater and more honourable than the body; in time, for it was earlier; and in power, for it not only institutes the temporal power but also has the authority to judge it, while the Pope cannot be judged by any man, except in cases of heresy.” The pope entrusted temporal authority to the emperors but retained the right to reclaim that authority “in virtue of the ‘plenitudo potestatis’ which he possesses as the vicar of Christ.” Indeed, the temporal power of the pope was so complete that Hostiensis considered it a mortal sin for a temporal ruler to disobey the pope in temporal matters. This view of papal authority in temporal matters also applied to the kingdoms of non-Christians. For Hostiensis all sovereignty had been taken away from non-Christians and transferred to the faithful when Christ came into the world. “This translation of power was first made to the person of Christ who combined the functions of priesthood and kingship, and this sacerdotal and kingly power was then transferred to the popes.” Non-Christians were thus subject to Christians but could maintain sovereignty over their lands so long as they recognized the church as superior. If non-believers failed to recognize the lordship of the Church, however, sovereignty could be taken away from them by the pope and transferred to Christian rulers. Hostiensis’ influence lasted well into the seventeenth century. His thought played an especially central role in Spanish theories of empire during the age of discovery. Both Juan Lopez de Palacios Rubios and Fray Matias de Paz, who were recruited by King Ferdinand of Spain in 1512 to help legitimate Spanish title over the New World, based their justifications of Spanish sovereignty over the New World on Hostiensis’ ideas on papal temporal sovereignty.
In literature
He is mentioned in the Paradise of Dante's Divine Comedy.
