Medieval causalities of birth defects interconnect medical and literary texts, which in turn reflect religious attitudes. Arguably religious or philosophical notions influenced, and in many cases predated, the medical discourse, all of which notions fed into literary texts – as many of the essays included in this volume similarly attest. The modern separation of religion from science, the spiritual from the secular, would have been nonsensical to the medieval mind.

How, then, did medieval normative texts – texts such as theological, philosophical or medical tracts, which reflect and reinforce commonly-held beliefs and cultural norms – explain the existence of congenital disability, that is, disability present from birth? In short, medieval texts tried to solve these problems by looking at sexuality, sin and conception. Conception here is meant in a dual sense, with concept as intellectual notion, and conception as physical begetting, in other words, a medieval aetiology of congenital disability. Previous research has more or less completely neglected the topic of congenitally disabled children, with the notable exception of John Boswell on the abandonment of children, and, in an oblique way, John Block Friedman on the monstrous races, but neither of these focuses on disability as the primary research question. This essay therefore traces the ‘absent presence’ in history of congenitally disabled people, who, in some ways, have been continuously present within history – all societies at all times have had disabled people – but whose history is not part of the mainstream and needs to be reconstructed from scattered, random references.

By way of introduction it is apposite to make a comparison with modern definitions and statistics. In 2012 the World Health Organisation (WHO) defined birth defects, or congenital anomalies, as ‘structural or functional anomalies, including metabolic disorders, which are present at the time of birth’. In terms of causality, however, the WHO estimates that approximately half of all cases of congenital anomalies cannot be assigned to a specific cause. What makes definition even more difficult, for the modern as much as for the medieval incidence of congenital impairment, is the continuum-like nature: as Judy Sture asks, ‘When is a condition a defect, and when is it an extreme of normal development?’