At the beginning of his Friar's Tale, Chaucer offers a succinct yet challenging excursus on demonology, which raises the issue of how demons manifest themselves to human beings, in order to be seen, communicate with their victims, and generally pursue their mission of inflicting harm on humankind. This understudied passage is of significance for many reasons, not least because Chaucer raises the spectre (so to speak) of the walking dead, insisting on allowing space to the terrifying thought that the dead can rise from the grave, their bodies having been taken over by demons. Here is the stuff of what has become known as the ‘ghost story’ and/or ‘horror fiction’. Further, and the focus of the present essay, is what the excursus reveals about late-medieval ideas and debates concerning what I shall call demonic ‘prosthesis’.

Following the Oxford English Dictionary, I employ the term prosthesis to denote ‘the replacement of defective or absent parts of the body by artificial substitutes’. This is a medical usage, which came into vogue in the early eighteenth century, following on from a much earlier grammatical denotation of the addition of a letter or syllable, usually at the beginning of a word (cf. the post-classical Latin term prosthesis, derived from the ancient Greek πρόσθϵσις, meaning ‘addition’). Currently, the term is in widespread use in discussion of the making and fitting of substitutes for limbs lost through surgical amputation or which were lacking at birth.

Demons and angels (for demons are fallen angels) have never had human bodies; they do not know what it feels like to be human (and, being superior creatures in the chain of being, have neither any individual need to know nor any particular reason to want to know). Therefore their lack is total. Not just a single body part but an entire body is needed, must be added to their existing, purely spiritual, forms. Here is prosthesis conducted on a scale which is total, inclusive, enveloping – and those angels and demons are not only the subjects, the recipients, of enhancements and extensions but also their creators, practising self-prosthesis under the general management of the divine will. But what prosthetic material was available to those creatures? There were the elements, especially air.