Proelefsiology (Eurasian: Prosiologia; Solvinian: προέλευση; Dovahzul: Kiinsetraas) is the study of the origins and relationship between Novem Deos and Mos Maiorum. Historically, the Maiorist Government of Eurasia has been extremely tolerant towards Novem Deos, even permitting that Deosian holidays are public holidays, something granted to no other religion in the Eurasian Empire. Several Emperors of Eurasia have been Deosians, and Deosians are the only members of Eurasian society permitted to practice their faith free of Imperial meddling.
The theological theory for the connection between the two faiths is cosmonogic in nature. Both the College of Pontiffs, who are the governing body of Maiorism, and the High Archprimate of Novem Deos, claim that the two faiths share the same origin. Many major theologians support this theory. The two faiths also share a historical connection, as Deosian merchants helped to build the Laurentine Republic into the regional power it became. Further, Deosians form the backbone of the Eurasian merchant class, as well as the medical and scholarly classes.
Maiorism and Novem Deos have a very similar creation mythos. Maiorism holds that the world was originally nothingness, from which came the the Earth (Gaia), who then birthed the sky (Uranus). The two then birthed the First Gods, who then birthed the Dii Consentes. Novem Deos holds that originally there was static immutability, from which was birthed Sithis, who sundered the stasis and created the universe, which then birthed the et'Ada, the First Ones, who then either birthed or became the Nine Divines (and the Aedra). The similarity between these two origins, as well as the similarities between the gods themselves, lead many theologians to claim the two faiths are "sister religions." They came from the same origin, but merely over time ascribed to it different names and characteristics.