Written by the seventeenth-century Franciscan theologian Ludovico Maria Sinistrari, Demoniality; or, Incubi and Succubi is an unusual work of Catholic demonology concerned with the nature of beings traditionally described as incubi and succubi. The manuscript remained unpublished during Sinistrari’s lifetime and became widely available only in the nineteenth century, after publisher Isidore Liseux reported discovering a Latin manuscript in London in 1872. Liseux published a Latin and French edition in Paris in 1875, followed by the Latin and English edition in 1879.

Sinistrari begins with the concept of “demoniality”, discussing how theologians classified supposed sexual relations between humans and supernatural beings. He considers earlier authorities, including Augustine and Thomas Aquinas, as he works through questions about the physical nature of incubi and succubi and whether reported encounters with them could be considered material rather than imaginary.

The treatise becomes particularly distinctive when Sinistrari questions whether all such beings should properly be understood as demons. He proposes the existence of rational creatures possessing both body and soul but differing from human beings. He compares these supposed beings with figures described in earlier religious and classical traditions, including fauns, satyrs and other spirit-like creatures, and asks whether they are born, die, reproduce and are capable of salvation or damnation.

The work also addresses witchcraft, sorcerers, demonic pacts and the theological classification of alleged supernatural encounters. Throughout, Sinistrari attempts to reconcile inherited stories and demonological traditions with Catholic theology and legal reasoning.

These arguments belong to the religious and demonological framework of early modern Europe and are not evidence for the actual existence of incubi, succubi or other supernatural beings. Today, the work is particularly valuable as a historical source for the study of demonology, theology and the ways early modern writers attempted to classify supernatural phenomena.