The outsider is coming back in. That is the message of the new Tate Britain show.
It takes the sort of art that for decades has been largely overlooked as the faintly ludicrous domain of the mere craftsman or the enthusiastic amateur, the untutored or the insane, into the hallowed halls of the cultural establishment.
From the Renaissance, Western art history was dominated by attempts to render the world in a life-like manner. But when descriptive techniques had finally been perfected, taken to their extremes by photorealism, it was something more than just mimicry that emerging modernists sought.