If we regard Satan as the essence of pure evil, then, logically, he should not be able to manifest on the material plane, for the same reason that the ‘Forms’ of Classical Greek philosophy cannot: our world is a realm of hybridity (or, in mystical/religious terms, compromise, dilution, corruption) and there is no room in it for an unadulterated principle. Indeed, because ‘good’ and ‘evil’ need a world full of living beings (since a moral principle cannot exist without moral agents), they must remain external to that world, their emanations experienced and interpreted ambiguously. This reflects a certain orthodox religious view of Satan – he is an outsider, and his modus operandi is to tempt people into doing evil through their own thoughts, words, and actions.

However, this is not the only ‘orthodox’ religious view of Satan’s influence. Some fundamentalist Christians, for example, agree that he cannot physically manifest himself on God's clean Earth, but at the same time believe that he can appear to mortals in an insubstantial kind of way. Because he cannot materially interfere with God's creation, he is limited to trickery and illusion, as indicated in his epithet “The Father of Lies”, given to him in John 8:44. At the same time, though, there is biblical precedent for conceiving of Satan as the absolute ruler of the material realm – John also refers to him as the “Prince of this World” (John 12:31, John 14:30), and in the Second Epistle to the Corinthians the Apostle Paul describes Satan as “the god of this world” (2 Corinthians 4:4). In this view, the Devil's powers may amount to nothing more than particularly snazzy sleight of hand, but enough mortals have been taken in by his tricks to give him de facto control over Earth.

Other believers, however, credit Satan and his minions with the power to physically interfere with the material world, most obviously in the context of demonic possession. As discussed in chapter four, possession and exorcism are commonly imagined to be vital elements of Catholic doctrine, especially by Catholicism's detractors: in the twentieth century (and the early twenty-first) horror media continued this exaggeration but treated the subject more seriously, albeit with a certain amount of artistic licence.