Demonology is the study of demons within religious belief and myth. Depending on context, it can refer to studies within theology, religious doctrine, or occultism. In many faiths, it concerns the study of a hierarchy of demons. Demons 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 jinn, 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.
According to some societies, all the affairs of the universe are supposed to be under the control of spirits, each ruling a certain "element" or even object, and themselves in subjection to a greater spirit. For example, the Inuit are said to believe in spirits of the sea, earth and sky, the winds, the clouds, and everything in nature. Every cove of the seashore, every point, every island and prominent rock has its guardian spirit. All are potentially of the malignant type, to be propitiated by an appeal to knowledge of the supernatural. Traditional Korean belief posits countless demons inhabit the natural world; they fill household objects and are present in all locations. By the thousands they accompany travellers, seeking them out from their places in the elements.
Greek philosophers such as Porphyry of Tyre (who claimed influence from Platonism), as well as 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.
Not all spirits across all cultures are considered malevolent. In Central Africa, the Mpongwe believe in local spirits, just as the Inuit do; but they are regarded as inoffensive in the main. Passers-by must make some nominal offering as they near the spirits' residence. The occasional mischievous act, such as the throwing down of a tree on a passer-by, is believed by the natives to be perpetuated by the class of spirits known as Ombuiri.