Conflating perception with judgment: the example of the Loudun Trial (1633-1634)

On a frigid December morning in 1633, Urbain Grandier, a catholic priest living in the French city of Loudun, is arrested at his home. The magistrate who has brought him the arrest warrant, the baron de Laubardemont, is the King’s special envoy to investigate what will be later considered as one of the most notorious case of witchcraft in the history of France.

The plot began a year earlier, in the Ursuline convent of the town, where a few of the seventeen nuns and the prioress Jeanne des Anges, started to feel unwell. The illness was quickly labelled as one affecting the mind, because many of the nuns were behaving oddly: they were strolling aimlessly around at night, crying frequently for no apparent reason, and expressing unusual desires. The prioress herself, Jeanne des Anges, said she was suffering from delusions and nightmares, and that her novices witnessed disturbing apparitions within the priory. The name of Urbain Grandier would be finally uttered, and the ecclesiastical jurisdiction alerted.

The behaviour of the nuns and the ‘unnatural’ scenes the investigators would witness the following days inevitably led to the opening of a case against Urbain Grandier for allegation of witchcraft. After a long and procedural investigation (the file amassing a weight of not less than 4,000 pages), Grandier would be condemned to death by burning. The unfortunate was executed the 18th of August 1634.

In these times, France was slowly recovering from recent wounds: the Reformation profoundly marked the country, and the King, a catholic, sought to regain control over the cities still influenced by the Huguenots. First and foremost, the wound was one of trust, and the reconciliation with the populace would only be far ahead. The city of Loudun was the stage of tensions and divisions, to the point of being threatened with destructive retaliation from the King himself. For the historian and philosopher Michel de Certeau, the Loudun possession unfolded at a time of psychological and social mutations, where science and its method were progressively replacing bigotry and superstitious knowledge (Certeau, 2005). The metamorphosis is illustrated by the very presence in the investigation panel of the Grandier case, of physicians and apothecaries along with representatives of the church and the crown. There was now a need for objectivity.

In this context, how could a trial based on fictitious allegations and superstitious precepts have led to such a tragic conclusion? The first reason is political, Grandier had a powerful nemesis in the person of the Cardinal de Richelieu, to whom the Baron de Laubardemont was plainly devoted. There is a second, more intriguing reason: a significant part of the jury – physicians included – was convinced of the magical extent of the case. By all means, jurors certainly relied on second-hand accounts of some shady witnesses, but the experts in the panel, the experts themselves, saw the devil at work. Or did they, really? Rogier, Cosnier, Carré and Duclos, the medical doctors in charge of the case, wrote, after attending an interrogation of the nuns in April 1634: “Nous avons jugé qu’il y a quelque chose qui dépasse la nature” (“We have judged that there is something beyond nature”). However, there is something deeply equivocal in the report of the physicians, something that could expand to and even explain the whole case: it is the conflation of perception with judgment. In the words of one of the judges, Mgr. de La Rocheposay “I’ didn’t come here to see if the possession is genuine. I already knew it is the case” (Certeau, 2005).

The Loudun trial remains an interesting example of a witness’s ability to bring his eyes to the point of lying. This apparent distortion between the percept and its cognitive processing might be considered as the basis of modern investigation in psychology and neuroscience: questioning the difference between believing and seeing, between what passes the retina and what sense one makes of it. Consequently, to understand how the mind makes sense of the world, we need to explore how it deals with uncertainty, what it cannot discern fully, what it needs to fill in the perceptive gaps with. More than two centuries after the Loudun possession, William James wrote, in his notorious Principles of psychology: “The brain is an instrument of possibilities, but of no certainties. But the consciousness, with its own ends present to it, and knowing also well which possibilities lead thereto and which away, will, if endowed with causal efficacy, reinforce the favourable possibilities and repress the unfavourable or indifferent ones” (p. 141, James, 1890). In James’ words, our actions are the product of our ability to distil possibilities into certainties, a singularly appealing perspective in the era of the Bayesian brain.


de Certeau, M. (2005). La possession de Loudun. (Gallimard, Ed.), La possession de Loudun (Folio Hist). Paris.

James, W. (1890). The principles of psychology (Vols. 1 & 2). New York Holt.