The last month in China has seen a range of reactions to the rescue of several hundred slaves, including children, from Chinese brickyards. In the cities there was shock; in the villages, where the victims came from, people knew that kidnapping is neither a new nor an isolated phenomenon. In the government, there was embarrassment: the existence of slavery cast something of a shadow over the party's current promise of a "harmonious society".

There was another, more unexpected result: the Southern Metropolis Weekly published an interview with the writer Wu Si, who argued cogently that both local tyranny and slavery had a long history in China, and that neither would be eliminated without democracy and the rule of law. His argument was simple: historically these things happened because the good behaviour of officials had depended on the vigilance of their superiors. Today, he said, the core power structure remained unchanged. "It is," he said, "still an upwardly responsible pyramid." Just as in the Qing dynasty, slavery is illegal today, but the law is not just insufficiently specific, as the national lawyers' association pointed out this week, it is also ignored. And just as in the Qing dynasty, senior officials complained that subordinates took bribes to flout the law, lied to superiors and resorted to obfuscation and delay if ordered to enforce it.

Many village heads are now elected in China, but, as Wu pointed out, the more powerful figure of the party secretary is not. "Democracy may not solve this problem," he said, "but a lack of democracy has caused it ... throw the crooks out by casting votes. And separation of powers, too, so that one individual can no longer mislead the public. An independent disciplinary department, an independent judiciary, an independent legislature." It is a measure of the government's wider problem of legitimacy that the Southern Metropolitan Weekly has not yet been closed down for heresy against the Communist party. Indeed, as the party prepares for its 17th congress this autumn, the word democracy is on the lips of the party elite; the difficulty is to determine what they mean by it.

Two years ago, the Chinese government published a white paper on democracy that opened with the stirring proposition that "democracy is an outcome of the development of political civilisation of mankind. It is also the common desire of people all over the world". Earlier this year the prime minister, Wen Jiabao, announced that "democracy, law, freedom and human rights" were not exclusive to capitalism.

But the white paper went on to explain that "democracy with Chinese characteristics" had been the party's gift to the Chinese people and there is little sign that this has changed. On June 25, Hu Jintao, the party general secretary, told an audience at the Party School, the communists' most important thinktank, that "greater participation" by the people was desirable - as long as it did not jeopardise the party's rule.

In Hu's view, wider consultation and a slightly wider franchise within the party for senior posts should just about do it. "Chinese characteristics" seem set to remain firmly in force. But this is unlikely to satisfy the demands of a population that has seen the promise of prosperity falter as the wealth gap widens and the rich and powerful pillage the public good. Outside party circles, the democracy discussion is much more radical.

Nearly 25 years ago, Wei Jingsheng, an electrician from Beijing Zoo, shot to fame with his famous wall poster, the Fifth Modernisation, pasted on that briefly tolerated bulletin board of political debate, Democracy Wall. It was an open challenge to Deng Xiaoping, whose "four modernisations" announced his intention to liberalise China's socialist economy. When Wei argued that China would not be a modern country if it did not also modernise its political system, he paid for his temerity with many years in jail. Twenty-five years on, his argument is gaining ground.

Last year a conference paper called for the party to split into two factions and contest elections. The author of that paper escaped sanctions. The party's conservative approach is unlikely to silence the growing number of voices who, like Wu, point out that the ills that afflict the legitimacy of party rule - corruption, arbitrary local tyranny and a legal system that remains firmly under the thumb of the powerful - are unlikely to be fixed from above. Authoritarian, top-down systems do not allow information to reach the head of the dinosaur with the speed required to allow leadership to run an effective government, as the Qing emperors discovered. And even when news gets out, local officials are aware, as they always have been, that the emperor is far away.

The difference is that increasing numbers of citizens know better. They are organising themselves into a bewildering range of pressure groups and action committees, despite restrictions on civic organisation, learning how to take action and pressure officials to obey the law of the land. In a growing number of articles, writers and intellectuals are challenging the proposition that the party has a divine right to the monopoly of political power - and the government no longer feels able to silence them.

· Isabel Hilton is editor of chinadialogue.net