Demonology is the study of demons and their classifications, aaaaaand that's about it. Honestly, that's just it. Most demonologists I know seem to be more focus about the possible origins of a demon based on their historical and mythological background than they are about their powers and weaknesses that can be used to defeat it. Completely rubbish in my opinion. If you want to know about demons, find a warlock or cambion and ask them to teach you about them. Trust me, it's much quicker and easier than to sit through hundreds of books.
It is primarily based on the Bible (Old and New Testaments), the exegesis of these scriptures, the scriptures of early Christianity philosophers, hermits and the associated traditions and legends incorporated from other beliefs. It is speculated that the study of demonology was started by King Solomon of Israel.
The study of demonology became popular with the rise of Christianity, and categorized demons in several different ways, and included the reassignment of other supernatural beings, like pagan gods (such as Pluto, Isis and Kali) and Fae, into demonic entities.
Description
Since Early Christianity, demonology has developed from a simple acceptance of the existence of demons, to a complex study that has grown from the original ideas taken from Jewish demonology and Christian scriptures. Christian demonology is studied in depth within the Roman Catholic Church, although many other Christian churches affirm and discuss the existence of demons.
They may be nonhuman, separable souls, or discarnate spirits which have never inhabited a body. A sharp distinction is often drawn between these two classes, notably by the Melanesians, several African groups, and others. The Islamic Djinn, for example, are not reducible to modified human souls. At the same time these classes are frequently conceived as producing identical results, e.g. diseases.
Greek philosophers such as Porphyry, who claimed influence from Platonism, and the fathers of the Christian Church, held that the world was pervaded with spirits, the latter of whom advanced the belief that demons received the worship directed at pagan gods.