Van Gogh is thoughtfully treated. Gompertz likens him in character, and art, to El Greco, and shows how he inspired later expressionists like Bacon. This sort of cross-period comparison is always enlightening to the student. And Gompertz writes well on Cubism. He has an obvious interest here, and so out go the dollops of references to pop culture, in comes some critical bite. The Bauhaus chapter is useful too. His taste, inevitably, becomes quite clear through the book, so it is no surprise when he is enthusiastic about Minimalism, particularly Judd — he had earlier professed his admiration for Apple computer designs, comparing them, oddly, to the paintings of Seurat. But he cannot be exciting about Minimalism: "There are the twelve steps and the eleven spaces between them. Each step is 22.8 centimetres deep, separated by 22.8 centimetres. Unlike traditional sculpture, there is no hierarchy to this work." It may read like a description of Ikea shelving, but that is not Gompertz's fault — the work, Judd's Untitled (Stack), looks just like Ikea shelving. This problem of dreary description runs right through the chapters on Suprematism, Pop Art, Conceptualism, Postmodernism; but how are you supposed to write substantially, and entertainingly, about things of no substance? Gompertz makes a brave effort, but the starkness of print only emphasises the shallows, and it suggests that the fun Gompertz — and so many others — found in modern art was more the glamour of the museum than its exhibits.

Unlike most who have championed modern art, Gompertz mentions the sceptics' view. He understands that the vulgarity of the art market is off-putting to the public, and accepts that the "price is being driven up by freshly minted bankers and shadowy oligarchs, ambitious provincial towns and tourist-orientated countries wanting to ‘do a Bilbao'". He also understands how tricky it is for contemporary artists to shock the establishment — as, of course, they must — now that they belong to it. Gompertz may know about scepticism, but he has none of it himself. The humility of his tone is a strength of the book; but it comes from real awe at the authorities of Modernism. He needs us to know that "museums are academic institutions full of very clever people", and if they often resort to pretentious jargon it is only because of the stress of having to communicate their subtlest understanding to a "first-time visitor". Fitting Duchamp into a layman's brain is as impossible as pouring the ocean into that sandy ditch.

Gompertz is totally in thrall to the art world. Of a smashed auction record, he writes: "The price is a testament to the lasting power of Giacometti's expressive sculptures." What could the price have to do with the expressiveness? He believes that Malevich, of the black squares, "is asking a great deal of the viewer". Really? More than Rubens? No. Much less. But we will give Rubens more because he gives us so much more. Gompertz believes and believes, and is upset by anyone "blithely dismissing a revelatory work" because they lack "the courage to believe". There is courage to believing in the significance of a black square, for sure — the black square was one of art's "great seismic moments, to rank alongside the discovery of mathematical perspective[!]... and Duchamp's urinal" — but there is also courage in doubting, especially now. He asked us not to judge art as good or bad, but to leave all that to time; well, time in this sense is only the record of human judgments. Really, he is asking us to leave all the judging to the authorities of Modernism, they who nowadays judge for time. They decide what goes in a museum, and therefore what lasts. They actually ensure that time never has his natural say on Modernism. "Modern art... is not a long-running gag being played by a few insiders on a gullible public." No, often it is the insiders themselves who are the gullible victims.