In 1994, Francis Alÿs joined the regular hiring-line in the central square in Mexico City. Standing next to plumbers and carpenters with their hand-lettered signs touting their skills, his sign read "Turista", as he offered his ability to be an outsider looking in. Three years later, he returned to the square, the centre of city life, and the site of the annual Independence Day parade, and the "Grito de Dolores", the patriotic ringing of the bells at the National Palace which up to half a million people attend.

Arshile Gorky found it almost impossible to finish a painting. Something would always call him back. So he would go back and would add and retouch and tinker around over several years - sometimes over the course of a decade or two. “When something is finished,” he once said, “that means it’s dead, doesn’t it? I never finish a painting, I just stop working on it for a while. The thing to do is... never finish a painting.”

Modernist art movements are a lot like totalitarian regimes. They produce their declaratory manifestos, send forth their declamatory edicts, and, before you know it, a Year Zero mentality prevails: the past must be declared null and void. Seeking to overturn 1,000 years of Western civilisation with a universal aesthetic utopia of brightly coloured squares and boldly delineated lines, a confident Theo van Doesburg, founding member and chief theorist of the Dutch movement De Stijl, wrote, “What the Cross represented to the early Christians, the square represents to us all.

Walk into the gaping mouth of the metal container featured in Miroslaw Balka’s installation at Tate Modern’s Turbine Hall and you are plunged into a disorientating darkness. Unnerved, you shuffle forward, passing and perhaps finding comfort in the ghostly presence of other limbs, other bodies which are also shuffling uncertainly, all awareness of spatial relationships denied in the enveloping blackness.

That artists didn't just respond to the rapacious commercialism of the late 20th century, but actively contributed to it is hardly news. That the marketing of art can be part of the art itself  is something everyone now implicitly understands, even if it’s only through hearing Tracey Emin wittering about herself on television.