For more than three and a half centuries, the death of René Descartes one winter's day in Stockholm has been attributed to the ravages of pneumonia on a body unused to the Scandinavian chill. But in a book released after years spent combing the archives of Paris and the Swedish capital, one Cartesian expert has a more sinister theory about how the French philosopher came to his end.

According to Theodor Ebert, an academic at the University of Erlangen, Descartes died not through natural causes but from an arsenic-laced communion wafer given to him by a Catholic priest.

Ebert believes that Jacques Viogué, a missionary working in Stockholm, administered the poison because he feared Descartes's radical theological ideas would derail an expected conversion to Catholicism by the monarch of protestant Sweden. "Viogué knew of Queen Christina's Catholic tendencies. It is very likely that he saw in Descartes an obstacle to the Queen's conversion to the Catholic faith," Ebert told Le Nouvel Observateur newspaper.

Though raised as a Catholic, Descartes, who had been summoned in 1649 to tutor Queen Christina, was regarded with suspicion by many of his theological coreligionists. His theories were viewed as incompatible with the belief of transubstantiation, in which the bread and wine served during the Eucharist become the flesh and blood of Christ. "Viogué was convinced that … his metaphysics were more in line with Calvinist 'heresy'," said Ebert. The theory of foul play has been greeted with caution by scholars. Since Descartes's death on 11 February 1650, pneumonia has been blamed for robbing the world of the so-called father of modern philosophy.

Ebert rejects this as incompatible with the facts. In a letter written after his patient's death, Descartes's doctor, Van Wullen, described having found something wrong – which Ebert believes to be blood – in the philosopher's urine. "That is not a symptom of pneumonia; it is a symptom of poisoning, chiefly of arsenic," said Ebert, adding that Descartes asked his doctor to prescribe an emetic. "What conclusion is to be drawn other than the philosopher, who was well-acquainted with the medicine of his day, believed he had been poisoned?"