The Guitar Player by Georges Braque is one of the masterpieces of modern art. Painted in the spring of 1914, a few months before the good soldier Braque went off to win the Croix de Guerre on the Western Front, it is at once a summation and a recapitulation of the revolution called Cubism. The motor of that revolution was the creative partnership between Georges Braque, a Frenchman, and Pablo Picasso, a Spaniard, one of the key international relationships of the twentieth century. Roped together like mountaineers, in Braque's classic image, they entered into an intense collaboration – at times a veritable cohabitation – legislating the future, vandalising the past, completely subverting Western ways of seeing.

An entire tradition of visual representation was overthrown, as if a hand grenade had been tossed into the placid world of the reclining nude, the wedding feast and the woman reading a letter. Everything was shattered, discomposed, only to be remade anew, askew, back-to-front, inside-out, all-round. Space itself was reconceived and reconstructed. Instead of receding tidily into the background, as prescribed by traditional perspective, the forms in Cubist paintings advance towards the spectator. Landscapes become landslips. Still life pushes forward, begging to be touched, or sampled, or played. We see into things, round things, through things, without prejudice; we see the component parts of things; we see things become things. Looking at Cubist paintings is a question of immersion, a little like diving, or caving.