The question that has haunted Gerhard Richter's career is not "what should I paint?" but "whether I should paint at all." This productive uncertainty — the sense that painting is always on the verge of having exhausted itself, always surviving its own announced death — is what makes the retrospective at Tate Modern such a strange and gripping experience.

"I have no programme, no style, no direction. I have nothing. I don't know what I want. I am inconsistent, non-committed, passive."

Richter's self-deprecation is, of course, its own form of manifesto. The works that emerge from this stated incoherence are among the most demanding and rewarding of the twentieth century: the Photo Paintings, with their blurred, photographically sourced imagery; the Colour Charts, whose deadpan seriality conceals an almost philosophical rigour.