provoke reactions

What these two examples suggest to me is that we are barking up the wrong tree by trying to define installations. Installations do not all share a set of essential characteristics. Some will demand audience participation, some will be site-specific, some conceptual gags involving only a light bulb.

Installations, then, are a big, confusing family. Which brings us to the second question. Why are there so many of them around at the moment? There have been installations since Marcel Duchamp put a urinal in a New York gallery in 1917 and called it art. This was the most resonant gesture in 20th century art, discrediting notions of taste, skill and craftsmanship, and suggesting that everyone could be an artist. Futurists, Dadaists and surrealists all made installations. In the 1960s, conceptualists, minimalists and quite possibly maximalists did too. Why so many installations now? After all, two of this year's four Turner prize candidates are installation artists.

American critic Hal Foster thinks he knows why installations are everywhere in modern art. He reckons that the key transformation in Western art since the 1960s has been a shift from what he calls a "vertical" conception to a "horizontal" one. Before then, painters were interested in painting, exploring their medium to its limits. They were vertical. Artists are now less interested in pushing a form as far as it will go, and more in using their work as a terrain on which to evoke feelings or provoke reactions.

"Many artists and critics treat conditions like desire or disease as sites for art," writes Foster. True, photography, painting or sculpture can do the same, but installations have proved most fruitful - perhaps because with installations the formalist weight of the past doesn't bear down so heavily and the artist can more easily explore what concerns them.