Mysterious journeys of a spy with a mind on high matters

Cogito ergo sum : I think, therefore I am." Descartes's rational proof of his own mental being, followed up by the only marginally less famous " dubito ergo Deus est " ("I doubt therefore God exists"), figure among the most commonly cited philosophical axioms in Western thought; and it is appropriate that a biography of the man who so reasoned should be available to the general reader.

A. C. Grayling gives a full account of Descartes's childhood and travels, his formation in mathematics and physics, his scientific experiments, his epistolary friendships - with Huygens, Mersenne and, later in his life, Elizabeth of Bohemia - and the patronage of Queen Christina of Sweden, at whose court in Stockholm he died in 1650.

Grayling also charts his engagement in philosophical polemics, alongside the metaphysical dilemmas to which the mind-body dualism inherent in his conclusions notoriously gave rise. The historical and intellectual backdrop is full and readabe, illuminating key moments in the narrative, albeit with a tendency to caricature when it comes to the finer points of theological speculation.

The first biography of Descartes was published in 1691 by Adrien Baillet, and Grayling makes appropriate use of that, as well as of later ones, of Descartes's writings and of his extensive and revealing correspondence. His most radical hypothesis - openly and circumspectly acknowledged as such - is that Descartes, educated by the Jesuits at the Collège de la Flèche and at least superficially obedient to Roman orthodoxy throughout his life, was a spy for the Society of Jesus in his many travels. This, Grayling proposes, explains his presence at various mysterious locations at propitious historical moments, and the apparently eccentric routes he chose to reach them. Grayling further suggests that Descartes's choice of the United Provinces (the Netherlands) as his preferred domicile for the greater part of his adult life was less the result of a self-imposed exile, as of a meeting with the powerful Cardinal de Bérulle in 1628 - and of the suspicion that his activities were at odds with the military engagements of the French crown during the Thirty Years War.

This volume includes two appendices, which are devoted successively to an excellent summary of Descartes's philosophy (a useful undergraduate introduction) and a critical survey of some recent philosophical biographies. The endnotes are full and informative, and there are fine colour illustrations.

The most unsatisfactory aspect of this study lies in its problematic relationship with the French language. It is reasonable in a work of this kind to quote from primary texts in an extant (and usually excellent) translation. But on occasions when a brief quotation, book title, historical figure or place name is given in French, the orthography and accentuation can be described only as anarchic. Even the full French title of Descartes's most famous work, the Discours de la méthode pour bien conduire sa raison et chercher la vérité dans les sciences , contains on its first appearance three miswordings and two spelling mistakes.

General readers might also have expected an explanation of how the plural French term " sciences " (to designate all areas of intellectual inquiry) differs from its English homonym. There is an entertaining slip in the section on Pascal, Descartes's near-contemporary and rival. We are told: "Pascal carried out the experiment (on the vacuum) in the following year with his brother-in-law, Puy de Dome (sic)." Pascal's brother-in-law was in fact one Florin Périer, and the Puy-de-Dôme, its circumflex restored, was the mountain on which the experiment occurred. And there is an unnecessary number of "Dear Reader" moments, usually in the form of injunctions to "remember", "recall" or "note this". But Grayling acknowledges in the opening pages that his account is for the general reader and will likely be attacked by "salaried professionals". So be it.

If such irritants are overlooked, however, and the book read at a first attempt, as Grayling suggests, for the story, then he has produced an entertaining and largely credible account of a figure who, for all his bookish legacy, lived an adventurous life, and whose radical Francophone writings that paved the way for atheistic materialism coexisted, in this version at least, with an enduring allegiance to the Society of Jesus and its clandestine agenda.

Richard Parish is professor of French, Oxford University.