It is intriguing to be reminded that Duchamp's famous work 'Fountain', around which sanitary perfection the crowds have been eagerly jostling at Tate Modern, is in fact a duplicate of the artist's original. This is because the original, chosen by Duchamp in 1917 from ironwork supplier TL Mott in New York City, No 118, 5th Avenue, was their 'Bedfordshire' model which Duchamp upgraded to form his new work, entitled 'Fountain'. Typically, Duchamp played a witty practical joke here, but he also upended conventional assumptions about art at that time just as much as he upended the selected urinal. Today, the fact that 'Fountain' is one of several duplicates should not deter the art lover overmuch, unless he is hard-pressed, en route for a contemporary Tate Modern urinal. Apart from being a beautiful object in its own right, it can flush out bland assumptions about the true nature of art - and did so then.