At times like these, events crowd in on each other to remind us that change can be directed and progressive, rather than merely passive and preordained. At a material, scientific and technological level we have absorbed the idea of progress to a point at which it has become a banality.

Millions of individuals exercise choices that were once considered the prerogatives of gods. They can travel by air and even be taken into space. They influence governments and sometimes dispose of them. Their daily diet may consist of rare delicacies, and some of their diseases can be made to disappear with the easy digestion of a tablet.

But it was a different idea of progress that first became popular in the mid-19th century and now appears brash and naive. It was, certainly, founded on the fact of material advance - the sudden and greater ease of travel, improvements in sanitation and the reduction in disease which so impressed contemporaries.

In the advanced west these victories also seemed to signify a real moral progress. Nobody supposed that humanity was getting better at producing saints and geniuses, but there was a new confidence in the possibility of a well-ordered society.

The intellectual advances that were once the preserve of an educated elite had spread further. Once, the skeptical courtiers of the 18th century had sneered at superstition in gossipy little groups; a century later great masses of people debated great issues of religion and science, political reform and freedom of trade in public meetings.

Postcolonial sensitivities, aided by awareness of class and culture, have eroded that confidence. It was once conventional to suppose that this 19th-century advance represented a culture in every way superior to that of the non-European. Ethically earnest secularists and ruggedly Christian missionaries shared a common belief in the necessity of European progress - and that certainty has long since vanished.

But there is a further reason for skepticism. The history of the 20th century dissolved the connection between material or scientific progress and a better moral order. Technological advance was twice turned to the business of mass slaughter in global war, as well as to genocide and ethnic cleansing. Material progress was seen to mingle with moral regress. The model T Ford and the gas chamber were the inventions that defined the century.

Meanwhile, the idea of a grand narrative in the human sciences has fallen out of fashion. Christian providence, Freudian psychology, positivist science, Marxist class consciousness, nationalist autonomy, fascist will: all have attempted to supply narratives that shape the past. When it came to practical politics, some of these narratives proved to involve repression and death. The liberal idea of progress might not be bloodthirsty, but as a unifying explanation it was seen to share in the defects endemic to all general theories. It was self-satisfied, and selected evidence to suit itself - so that a belief in progress just seems to favor the historical winners while the losers get shunted aside.

And yet the idea of progress has a long history, starting in early 5th century BC Greece. No idea as purposive disturbs the lists of Babylonian kings. Babylonian astrology was designed to prove the repetition of world periods, while Hinduism, a religion of repetitious ritual, ensured that pre-modern Indian civilization would be stubbornly uninterested in critical history. What happened in classical Greece was sudden and unheralded.

The defeats inflicted on the Persians had instilled Greek intellectual self-confidence and democratic experimentation. But that was balanced by caution about the jealous gods with their capacity to wreck human prosperity. That caution is reflected in Thucydides' History of the Peloponnesian War, in part an illustration of the role of freakish chance in human affairs. Progress here was a real advance, but it was impossible to rely on its continuance.

The 18th-century philosophers also recognized the precariousness of progress - and so spent so much time excoriating fanaticism and superstition. In Candide, Voltaire satirized all those who think that present suffering can be assuaged by faith in the idea of an ultimate purpose.

Historical progress did exactly the job required of it by the Enlightenment thinkers: it showed history as a series of episodic fits and starts. Their pages show that it is possible to believe in progress without also subscribing to its inevitability - and it is the inevitability of progress which has been the main point of attack by historically-minded critics.

The philosophers were also respectful of the fact that customs vary. Voltaire, so often thought to be an apostle of unchanging reason, thought that Islamic societies were "so different from everything we are used to that they should show us how varied is the picture of the world".

These philosophic historians measured human variety against the standard of a fundamental human nature, those passions and affections that are a constant feature of the human condition. Their historical conclusions issued from judgments shared by both reader and author about what constituted luck and cruelty, treachery and loyalty, misery and joy. Without some kind of common understanding of what such terms mean, it is difficult to see how history of any kind can be written.

In this restricted sense, progress is a real, if episodic, feature of history, and knowable to posterity. Many critics, impressed by the remoteness of the past, have denied the possibility of real historical knowledge. This is why René Descartes sneered that "historians of Rome know no more than Cicero's servant girl". Both stand on the margins of events to which they can never be admitted. This is a reminder of the great strangeness of the past and of the arrogance involved in applying present assumptions to history. But that insistence on the otherness of the past can lead to the belief that it is dead and so cannot be understood. And that kind of skepticism is a form of nihilism.

In fact, the existence of a common humanity makes it possible to understand how past peoples lived, thought and acted. The quality of choices and decisions can then incline us to find parallels, comparisons and contrasts. And the observation of progress that emerges is something more certain than a common illusion, and less certain than a genetically programmed necessity. It seems a necessary idea, if not an inevitable one.

This is an edited extract from Cassell's Chronology of World History, by Hywel Williams, published later this month

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