Using an interdisciplinary approach, including historical semantics, medicine, natural philosophy and law, it considers a neglected field of social and medical history and makes an original contribution to the problem of a shifting concept such as 'idiocy'. Medieval physicians, lawyers and the schoolmen of the emerging universities wrote the texts which shaped medieval definitions of intellectual ability and its counterpart, disability. In studying such texts, which form part of our contemporary scientific and cultural heritage, we gain a better understanding of which people were considered to be intellectually disabled and how their participation and inclusion in society differed from the situation today.