I recently wrote an article about two installations by the young artist Nina Saunders which had featured prominently in the annual sculpture exhibition in the grounds of Jesus College, Cambridge. Saunders specialises in heavily pregnant, lavishly upholstered arm chairs - deceptively comfortable to the eye, impossible to sit in. How, I asked her, had she come to be selected for an event whose leading lights were world-famous veteran sculptors such as Richard Long, Anthony Gormley and Eduardo Paolozzi? She answered without hesitation: Charles Saatchi had bought seven of her pieces to add to his collection.
In practical terms this had enabled Nina Saunders to carry on producing new work (the cost of manufacturing each of her upholstered pieces is very high). But more importantly, the golden seal of Saatchi approval had also established her name on the "Young British Art" circuit that now dominates the contemporary art world.
Young artists such as Nina Saunders, or Turner Prize nominees Fiona Rae and Gary Hume - a show of whose work opens at the Saatchi Gallery next week don't have any trouble acknowledging that the private collector who spends lavishly on new art is, in fact, shaping the contemporary artistic landscape.
By keeping the artist in pocket, loaning his or her work to the national galleries - or, in the case of Charles Saatchi, displaying it on the walls of his own museum - these buyers may also be defining the experience and taste of the gallery-going public. Saunders and her peers are entirely comfortable with the idea that the preferences of an enthusiastic patron may decide who counts - and who does not - on the art scene in this country; who gets shortlisted for prestigious awards such as the Turner Prize (Saatchi himself presented the award in 1994; another year he was the patron of all four-short-listed artists); whose work is bought by influential overseas collectors and, of course, at what price.
Art critics, on the other hand, really have a problem with the idea that the buying and selling of art might lastingly influence public taste. They are particularly nervous when the buyers are individuals whose purchasing credentials come from the business world.
Last year the Austrian-born engineer Josef Froelich and his Hungarian wife Anna, previously collectors of scientific instruments and vintage cars, latterly patrons of contemporary art, offered to lend more than 300 of the works they own by American and German artists to the Tate Gallery, for display in its new Bank-side extension. When the news broke the British response was panic. Critics worried that the supposedly idiosyncratic tastes of rich foreigners would be imposed on the British nation: "Let's hope we get the good stuff," wrote Adrian Searle in the Guardian, meaning Bruce Nauman, Joseph Beuys, Sigmar Polke, not unknowns such as Blinky Palermo and Rosemary Trockel.
Discerning critical judgment and a thick chequebook cannot go hand in hand, according to the critics. Hence Brian Sewell's characteristically ill-considered assessment of Charles Saatchi's art purchasing as "just futures dealing - it might as well be coffee".
But what chance is there that the great art of our era will be identified by the acquisition policies of our national galleries? The accountability of curators and museum committees to their funding bodies requires that they play it safe. Unlike the private collectors, they are in no position to jettison mistaken purchases, nor to squander funds on speculative acquisitions which may or may not prove to be of lasting value. Committee purchases are much more likely to prove banal than brave.
The relationship between Charles Saatchi and the "young British art" he is currently buying is more subtle and thought-provoking than the critics' knee-jerk hostilities suggest. Saatchi is not just one of those buyers who can boost or depress a career at whim. He is what you might …