“DEVIANCE” AND “CRIME” are terms usually applied to behaviour or actions. Can an idea be deviant or criminal? Or is this what we say about the person who holds it? The censorship of ideas in thirteenth-century Europe offers particular insights into the ways in which ideas themselves can be categorized as deviant—that is, denigrated by normative systems—and outlawed or perceived to be outside the law. By professing the idea, a person could be condemned and punished, but the idea itself also carried the taint of crime. This impression, while not based on a legal definition of crime or involving the absurd possibility of inflicting punishment on the idea, was nevertheless a perception shared by many people in the circumstances analysed here. The discussion below looks at the distinction between criminal people and, in the view of medieval protagonists, criminal ideas. It shows how legal measures criminalized ideas through the use of certain labels; and it identifies perceptions of ideas as criminal, even in the absence of legal measures. To draw out the powerful ways in which ideas can be treated as not neutral but criminal, the discussion concludes by showing how the criminal status of ideas could condition perceptions about people—even when those people were conscientious in their handling of the ideas and did not intend to be transgressive.

The ideas under discussion here are not socio-political, potentially revolutionizing a society or its government (as in the introduction of a commune system), but philosophical and religious. Censorship of ideas and investigations of culprits holding them were by and large carried out by the Church, with secular authorities performing punishments in cases of individuals found by the Church to be heretics. In general the ideas were religious, such as the belief in two deistic principles which Cathars were accused of holding. The focus of this article is marginalized ideas which were not religious in themselves, yet trespassed on religion by conflicting with central beliefs. This was the case with certain Aristotelian philosophical/scientific theories that caused controversy in academic circles in the thirteenth century. The theories were newly introduced into Latin Europe through the translation of ancient Greek and medieval Arabic philosophical texts over the twelfth and early thirteenth centuries. They sparked controversy because they were regarded as denying fundamental Christian beliefs.