The history of ideas has a history of its own, and it is not long. Peter Watson believes the first person to conceive of intellectual history may have been Francis Bacon, which places the birth of the subject in the late 16th century. In Greece and China more than 2,000 years ago, there were sceptics who doubted whether the categories of human thought could correctly represent the world, but the recognition that these categories change significantly over time is distinctly modern. Thanks to thinkers such as Vico and Herder, Hegel and Marx, Nietzsche and Foucault, the notion that ideas have a history is an integral part of the way we think today, and it surfaces incongruously in unlikely places. Thinkers of the right may rant against moral relativism and look back with nostalgia to a time when basic concepts seemed fixed for ever, but these days the right is committed to a militant belief in progress - and so to accepting that seemingly permanent features of the conceptual landscape may turn out to be no more than a phase in history.
Given the importance of the history of ideas to the way we understand ourselves, you might expect it to be a flourishing discipline, but that is far from the case. As Isaiah Berlin used to say, it is an orphan subject. Ever sceptical of abstraction, historians complain that it slips easily into loose generalisation. For philosophers, who tend to assume that questions asked hundreds or even thousands of years ago about knowledge and the good life are essentially the same as the ones we ask today, it is irrelevant. Very few economists know anything much about the history of their discipline, and the same is true of many social scientists. At a time of grinding academic specialisation, intellectual history seems a faintly dilettantish, semi-literary activity, and the incentive structures that surround a university career do not encourage its practice. More fundamentally, the history of ideas is a casualty of the growth of knowledge. Anyone who aspires to study it on anything other than a miniaturist scale needs to know a great deal about a wide range of subjects - in many of which knowledge is increasing almost by the day.
In these circumstances, a universal history of ideas seems an impossibly daunting project. Yet in Ideas: a history from fire to Freud, Watson gives us an astonishing overview of human intellectual development which covers everything from the emergence of language to the discovery of the unconscious, including the idea of the factory and the invention of America, the eclipse of the idea of the soul in 19th-century materialism and the continuing elusiveness of the self. In a book of such vast scope, a reader could easily get lost, but the narrative has a powerful momentum. Watson holds to a consistently naturalistic philosophy in which humanity is seen as an animal species developing in the material world. For him, human thought develops as much in response to changes in the natural environment - such as shifts in climate and the appearance of new diseases - as from any internal dynamism of its own. This overarching perspective informs and unifies the book, and the result is a masterpiece of historical writing.
Watson's sympathy for naturalism enables him to spot some crucial and neglected turns in the history of thought. Nowadays, naturalistic philosophies are usually connected with those Enlightenment beliefs which hold that humanity progresses through the use of reason. Watson notes, however, that Spinoza, a pivotal thinker who may well have had a greater role in shap- ing the early Enlightenment than better-known figures such as Thomas Hobbes and Rene Descartes, took a different view. He never imagined that human life as a whole could be rational, and in a lovely passage quoted by Watson he wrote: "Men are not conditioned to live by reason alone, but by instinct. So they are no more bound to live by the dictates of an enlightened mind than a cat is bound to live by the laws of nature of a lion."
In Spinoza's view, the capacity for rational inquiry may be what distinguishes human beings from other animals, but it is not the force that drives their lives - like other animal species, humans are moved by the energy of desire. This view reappeared in the 20th century in the work of Sigmund Freud, who took the further step of recognising that much of human mental life is unconscious. In conjunction with later work in cognitive science showing that there are many vitally important mental processes to which we can never consciously gain access, Spinoza's naturalism has helped shape a view of human beings that is different from the one we inherit from classical Greek philosophy and from most Enlightenment thinkers.
One of the curiosities of intellectual life is the persistent neglect by philosophers of non-western traditions. No doubt this is partly ignorance on their part. Beyond a smattering of Plato and Aristotle and a few scraps from the British empiricists, most English-speaking philosophers know practically nothing of their own intellectual traditions, and no one would expect them to have any acquaintance with the larger intellectual inheritance of mankind. A more fundamental reason may be the view of the human subject found in some non-western philosophies. The ideas of personal identity and free will we inherit from Christianity have often been questioned, but they continue to mould the way we think, and any view of human life from which they are altogether absent remains unfamiliar and troubling. Watson is refreshingly free from the cultural parochialism that still disables so much western thought. Ranging freely across time and space, his survey includes some enlightening vignettes of Chinese and Indian thought, and he gives a useful account of Vedic traditions in which human individuality is regarded as an illusion. For those who want something more engaging than the dreary Plato-to-Nato narrative that dominates conventional histories of ideas, this wide range of reference will be invaluable.
Inevitably there are gaps in Watson's account. His treatment of Buddhist philosophy is cursory - a surprising omission, given his naturalistic viewpoint. He concludes with some interesting thoughts on the failure of scientific research to find anything resembling the human self, as understood in western traditions. He asks whether the very idea of an "inner self" may not be misconceived, and concludes: "Looking 'in', we have found nothing - nothing stable anyway, nothing enduring, nothing we can all agree upon, nothing conclusive - because there is nothing to find."
This conclusion is also mine, but it was anticipated more than 2,000 years ago in the Buddhist doctrine of anatman, or no-soul. The thoroughgoing rejection of any idea of the soul was one of the ideas through which Buddhism distinguished itself from orthodox Vedic traditions, which also viewed personal identity as an illusion but affirmed an impersonal world soul: an idea that Buddhists have always rejected. For them, human beings are like other natural processes, in that they are devoid of substance and have no inherent identity.
The view of the human subject suggested by recent scientific research seems less strange when one notes how closely it resembles this ancient Buddhist view. Modern science seems to be replicating an account of the insubstantiality of the person that has been central to other intellectual traditions for millennia. It is an interesting comment on prevailing ideas of intellectual progress that one should be able to find such remarkable affinities between some of humanity's oldest and newest ideas.
John Gray's most recent book is Heresies: against progress and other illusions (Granta)