I make bold to say this because two happy coincidences have left me very well informed - and even more enthusiastic - about the play! First, a friend of mine lent me Alan Bennett's Untold Stories, which includes an account of the genesis of "The History Boys." And then I got to see the justly celebrated Melbourne Theatre Company production of the play!
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This production was fantastic. And it was very interesting indeed to see the characters played by different actors so soon after the film; most were good, some were very good and several (notably the headmaster, and the object of everyone's desires Dakin, who in this production looked like a singer from Duran Duran, perfect for 1983!) were even better than the original cast. The characters are richer and more complicated, and Irwin turns out to be dangerously nihilistic. But the main thing was seeing it work as theater, and learning just how much had been cut for the movie.
Besides lots of poetry it seems to me the very heart of the argument of the piece is lost in the translation to film: that there's something analogous to Henry VIII's decommissioning of the monasteries going on in results-oriented modern education. (It's mentioned in the film, but not enough for you to see it structuring the whole; I suppose the audience for a Hollywood film couldn't be expected know what was being referred to.) And that there's a connection between this utilitarian understanding of learning and history and the cynical and nihilistic politics of Thatcherism (and Neoliberalism more generally).
Abbreviated beyond recognition also is the viewpoint (centrally important to Bennett, methinks) characterized by Wittgensteinian reticence and the perspective of those who don't make history, and represented by Mrs. Lintott, the only woman in the play; but the lines where she claims Wittgenstein for the woman's view ("didn't he ride on the other bus?") have been dropped. Gone also is the idea that the precious thing that art and poetry and a sense of the past give us (if we're lucky enough to have a teacher like Hector) is similar in some powerful way to the consolations of religion.
I can see now why people said this was the best play they'd seen in years. Go see the MTC show if you can (it closes Saturday). Otherwise, read the play. And then - only then - watch the film and fill in the gaps.