Christian demonology is an orthodox study of the theological concept of demons, based on the Bible. It is not a science, but an imaginative concept. Demons were believed to be fallen angels, who had a rift with the 'working of God'. Satan and the demons became adversaries of humans, instigating them against God, by inculcating negative traits. These angels-turned-demons committed this act of their own free will and were liable to face God's eternal wrath. Humans cannot be 'possessed' by demons by the grace of God, however, they can be subjugated by demons. A book written on it in the early 20th century, titled 'War On The Saints', by Jesse Penn-Lewis, contains detailed information about what demons are, their ways and means of achieving cruel objectives, and ways to resist them. It was believed that in the early days of Christianity, the air was filled with demons, and people were likely to adopt false ways under their influence. It originated from the Jewish demonology and Christian sacred writings, evolving into an imaginative concept. These demons are neither omniscient nor omnipotent. Therefore, they cannot be at two different places at the same time. The devils sent emissaries to propagate evil, as they were malevolent. Nature and Classification of Demons According to this belief, their aim is to lure or induce human beings into committing sins and testing their loyalty towards God. Christianity put forth the belief that all temptations have three sources, namely, the world, the flesh, and the demon. According to the Bible, demons weaken a person by inducing diseases and defamation in their lives, or by scaring people with apparitions to make them sin. It also states how demons transform into idols or Pagans, which are revered by human beings, gradually turning them to the side of evil. Christian demonology also attempts to classify demons by their nature, the type of sin they subject human beings to, the months on which they have a stronghold, and other such features. Thus, there have been numerous versions of classification of demons. For example, Michael Psellus classified demons in the 11th century, as those which avoid daylight and cannot be seen, and fire demons residing far away from human civilization. In the 16th century, demons were assigned a month according to their missions and when their powers would be at its peak. This classification had a hint of astrology in them, along with religious implications.

• January-Belial
• Levithan-February
• Satan-March
• Belphegor-April
• Lucifer-May
• Berith-June
• Beelzebub-July
• Astharoth-August
• Thammuz-September
• Baal-October
• Asmodai-November
• Moloch -December

According to the passage of time and the culture which defined them, the classifications too were subject to drastic changes. Similar to their categorization, demons also had hierarchical positions in Christian demonology. Satan was considered the supreme demon or the prince of demons. Hell was thought to be a medieval kingdom, with demons being assigned different nobility. Sexuality in Demons According to the civilizations of Sumeria, Babylon, Jews, and Assyrians, there were both male and female demons. The only demon with a bisexual tendency was Asmodai. One school of thought advocated the belief that sins were a cause of demons, and all non-heterosexual inclinations were 'sin', therefore, demons must be both the sexes or bisexual. Another thought process stated that since angels were all male and demons were fallen angels, all of them had to be male. It was also believed that lust was an inherent characteristic of demons, and they were capable of possessing emotions like desire, love or jealousy. Still, some believed that they only possessed the incubus tendency to impregnate women. Similar to any other facet of demonology, even on this issue scholars have expressed diverse opinions. The common aspects of their nature, as intending to spread evil and cause harm to human beings, were, however, consistent with all the versions of Christian demonology.