One of the defects of contemporary philosophy is a lack of knowledge of the historical contexts in which philosophical ideas are produced. This is not entirely accidental. Especially in the English-speaking world, philosophers are anxious to set boundaries around the subject, marking it off from anything that looks irrational, or which current opinion finds somehow suspect. This strategy may promote clarity of thought, but essentially it amounts to the pursuit of respectabil- ity - a dreary ideal for philosophy. Nowadays the academy is obsessively secular. For most philosophers, anything that smacks of religion or mysticism is beyond the pale, fit only for the shelves in bookshops that deal with New Age cults.
The trouble with the attempt to purge philosophy of suspect influences is that it leads to a neglect of beliefs that actually inspired philosophers in the past. These were nearly always religious. Hegel's philosophy reproduced a Christian view of history, and Marx followed Hegel in seeing history as a purposive process - a view that derives from the idea of divine providence. Many contemporary philosophers believe that pursuing the sources of ideas betrays a genetic fallacy, which wrongly suggests that if a belief has a particular origin it cannot be justified in other terms. However, some views are indefensible and even incoherent when wrenched from their original conceptual framework. This is true of the teleological view of history advanced by Hegel and Marx, and of contemporary liberal conceptions of natural rights. Locke's liberalism was rooted in his version of theism. Without some such theological basis, the idea of natural rights that is at the core of his and other liberal theories is left hanging in midair. A great deal of seemingly secular philosophy is made up of religious leftovers of this kind.
Rene Descartes was an avowed Catholic believer, but he founded modern philo-sophy on a method of systematic doubt. Except in embracing this method, Des-cartes was far from being any kind of sceptic. As Anthony Grayling puts it in this brilliantly illuminating reassessment of the philosopher and his times, Descartes viewed methodical doubt as "an infallible recipe for the discovery of truth". He had very little in common with such contemporary sceptics as Michel de Montaigne - a genuine freethinker who used doubt to undermine all varieties of dogmatic belief (including the belief in human uniqueness). Descartes has more affinity with hermetic and occultist thinkers such as the Rosicrucians. As Grayling writes: "Hermeticists and Rosicrucians shared the desire to discover methods that would unify all knowledge and allow the practitioner to discover anything and everything, moving from discoveries in one area of thought to discoveries in another by infallible means. This is what Bacon and Descartes sought too."
Grayling insists that, in the end, Descartes belongs among the founders of the modern scientific world-view rather than with the mystics, but one cannot easily distinguish between the two. The greatest modern scientists have often linked their work with beliefs that lie well outside the boundaries of empirical inquiry. Isaac Newton devoted more time to trying to decode the numerological code he believed was in the Bible than he did to physics. Explaining why he rejected the vision of a world containing random events that seems to be implied by quantum mechanics, Albert Einstein famously declared that "God does not play dice".
By showing how Descartes's intellectual ambitions ran parallel to those of thinkers now consigned to the disreputable underworld of European intellectual history, Grayling shows him to be a more inter-esting - and problematic - figure than the closeted introvert featured in standard histories of philosophy. According to the account given in his notebook - no copy of which exists, but which has been reconstructed using contemporary reports - Descartes formulated his philosophy of methodical doubt after a day in a stove-heated room and an ensuing night of extraordinary dreams. Grayling points out that the dreams were remarkably similar to those described in Rosicrucian texts. It is known that Descartes had many acquaintances among the Rosicrucians. Can we be sure that the intrepid rationalist was not a secret intellectual ally of these hermetic thinkers? Grayling thinks it unlikely, and makes the intriguing suggestion that Descartes may have been a spy working in the service of the Jesuits, who formed contacts with the Rosicrucians as part of an intelligence-gathering operation. In the nature of the case, there can be no proof, but it leaves the philosopher looking a surprisingly adventurous figure.
Descartes was not intellectually adventurous, however. For all his advocacy of methodical doubt, he adopted the moral prejudices of his time slavishly. This is nowhere more clearly shown than in his view of animals as insensate automata - a ridiculous view whose truth he attempted to demonstrate in some disgusting experiments. Modern philosophy might have developed very differently if its founder had followed the example of Montaigne in applying a degree of genuine scepticism to the anthropocentric prejudice that consciousness is a uniquely human phenomenon. We might have a more interesting body of ethical theory, and a wider philosophy of mind. To this day, philosophers discuss the mind-body problem as if it applied only to humans. However, if there is a problem about the relations of mind and body, it applies as much to chimps and dolphins, dogs and cats and a host of other species as it does to the human animal.
The notion that we alone are conscious is an error inherited from western religion, not a result of scientific inquiry. The fantastical theory of Cartesian dualism - the idea that brain and mind are radically distinct but somehow interact - could probably never have arisen except in a culture whose view of humanity was formed by Christianity.
Like many philosophers, Descartes spent much of his life seeking, and find-ing, reasons for conventional beliefs. Yet we still cannot be sure what he himself really believed. Despite Gray-ling's investigations, Descartes remains in many ways a conundrum. Anyone who wants to understand the mystery that still surrounds the philosopher can do no better than turn to this book, a first-rate study of the history of ideas that has all the excitement of a thriller.
John Gray's Heresies: against progress and other illusions is published by Granta Books