Cyberspace is full of advertising. Such a statement sounds odd, given that the Internet is reputed to be a difficult place for advertisers. Indeed, it does require stretching the definition of advertising; but then, in a knowledge economy, the stretching of old definitions will be commonplace. So while it may be, as some predict, that the present free-for-all culture of the on-line world will be tempered with money and advertising, such advertisement will take unusual forms.

An advertisement is information, an expression and - in a knowledge economy - a product. Like any other product, it will, often enough, have to compete for a consumer's attention. It will have to be appealing, informative, and - like all valuable content - relevant. Advertising cannot rely, as it does in the age of television, on forcing itself down the gullets of perpetually gaping consumers.

Consumers will eventually be as comfortable with information products as they are today with more tangible industrial goods. They will also be as selective. Most importantly, people will not be dependent on a small number of limited - and hence expensive - sources of information that need to be subsidized by the mandatory consumption of advertising.

Advertising is sought after by quality content producers today for two reasons - to cover the cost of publishing, and, on the Internet, to make up for the non-existence of any convenient system of charging customers. So, these customers have to be serviced free of charge - and advertising comes to the rescue. However, as publishing becomes cheaper and more universally accessible, and efficient systems for electronic monetary transactions come into place, the need for such advertising will diminish.

When low costs allow everyone to become a publisher, there will naturally be a few islands of quality amidst a sea of mediocrity. Their creators will probably spend much more to maintain good content than most. They may not all want to cover these costs, but those who do will be able to charge their readers directly, thanks to technology. The millions of content-producers who do not charge will, strangely enough, find much in common with the new advertisers.

Free content providers will be accused of more than mediocrity. They will be - and are already, on the Internet - called unreliable, devoid of objectivity, irrelevant, trivial and often useless. By an odd coincidence, most advertisements are also called unreliable, subjective and irrelevant. This is not surprising. Free content is not produced solely out of altruism, but out of a knowledge-economy profit motive - boosting the reputations of producers and often acting, in effect, as advertisements for their other services.

Just as free content producers compete for attention by trying to be relevant, objective and useful - more like paid-for publications - so will advertisers struggle to improve their own, equally free, content. Advertisers will have to work to sell their primary product, the advertisement, to readers, on its own merit. The "real" product becomes secondary, obliquely promoted by the primary, information, product.

This competition-driven triumph of relevance in the knowledge economy will necessarily take time, for it depends on widespread familiarity with its workings. But the ultimate irony would be when, advertisers having realised that they produce information like anyone else, advertisement finally becomes editorial.