I stress the word "composers": the 36 living names listed this year are all producers of notated scores in the Western sense. Improvised or traditional non-notated music from other cultures is much less evident, though there is a late-night jazz concert from the Julian Joseph All-Star Big Band (19 Aug), and (also a late-nighter) a programme of Music from the Far East (4 Aug), with a contribution from the exciting Chinese virtuoso Wu Man and her ensemble. And the young Lebanese rising-star organist Naji Hakim, the late Olivier Messiaen's successor at La Trinite, includes an improvisation in his early evening recital (23 Aug), though that too is a venerable Western tradition - one of the first guest players on the Royal Albert Hall organ was a noted Austrian organist-improviser named Anton Bruckner.
Still, there has been one major shift since Glock's day. If you encountered a new work at the Proms in the 1960s - and for some time afterwards - you could be fairly sure of what you were going to hear. The language would be hard, uncompromising, almost certainly non-tonal. If it disturbed or annoyed you, tough - that was what progressive contemporary music was supposed to do.
The ascendant ideal was art pour epater la bourgeoisie (a bourgeois notion if ever there was one, but that's by the way). The British younger generation was in reaction against Vaughan Williams, and with him any composer who might at any time have been guilty of, as the then plain Mr Peter Maxwell Davies once put it, "dancing on the village green".
But now - well, there's really no guarantee what you might find. If the name on the bill is Arvo Part or John Tavener (24 July and 7 Aug respectively), you will probably hear music of a harmonic simplicity unmatched in Western music for several centuries. Tavener's language has become chaster, sparer and even less eventful since the piece by which he is here represented, The Protecting Veil, first became one of the great Proms hits of recent years at its 1989 premiere - the gorgeous shifting triadic harmonies at the start could almost be Vaughan Williams. If, on the other hand, the name is Kaija Saariaho or James Wood (29 Aug and 11 Sept), you will find the challenging experimental ethos of certain kinds of 1960s modernism very much alive.
To me, they both represent a mature experimentalism, free of aesthetic or political posturing, which can produce fascinating, roundly satisfying works in ways few of their pioneering predecessors could match. Regular, inquisitive Prom-goers have an opportunity to compare these riper fruits with two earlier modernist works which may well have survived the test of time: Pierre Boulez's early and surprisingly lush Le Soleil des eaux (25 July) and Gyorgy Ligeti's Melodien (16 Aug) - now there's a work whose relatively uncomplicated, mellifluous pattern-making today's audiences may well find easier to accept.
Between these extremes there is a fair bit of variety. American "post- minimalism" is heard in works by Michael Torke (14 Aug) and Steve Reich (7 Sept). Reich's recent City Life shows how far he has advanced from the obsessively repetitive products of the Seventies and early Eighties - there are losses as well as gains - but, like his younger compatriot Torke, he remains distinctly American, especially in the harmonies, which in themselves aren't that different from the succulent, bluesy chords of Copland, Bernstein or Stephen Sondheim.
Yet another, European kind of post-minimalism - harder-edged, dissonant and more than faintly politicised - is absent: no Steve Martland, no Louis Andriessen. Names like those would have broadened the Proms picture still further.
But there is no evidence in this year's line-up that it's still an advantage to hitch your name to an "ism". Composers such as Poul Ruders (21 Aug), Judith Weir (11 Aug), John Casken (26 July) and Oliver Knussen (3 Aug) remain wonderfully, refreshingly independent, aware of what's going on around them and strong enough to steer their own courses. Under the guise of an intimidating-sounding technique, "minimorphoses", Ruders in particular has discovered a fertile means of creating a very personal and appealing kind of lyricism, as his new Viola Concerto will show. Weir and Casken have been moving in broadly similar directions. And further good news is that Knussen's Chiara - originally scheduled for its Proms premiere back in 1986 - finally seems to be on course for completion in time for this year's season. Fingers crossed.
One "ism" that isn't represented is anti-modernism. Are the Proms the place for the works of the so-called Hecklers: Keith Burstein, Frederick Stocken and..? The evidence so far is that their bark amounts to rather more than their musical bite. But then there's the octogenarian symphonist George Lloyd, a cause celebre among the more fogeyish anti-moderns. Huge claims are made for his popularity (or potential popularity). Where better to test it than at the Proms?
The anti-modernists will have plenty to grumble about, though - which, one suspects, is what some of them really enjoy. After a few ominous back- stage rumblings, it seems that Luciano Berio's advertised new work has materialised (15 Sept): it is called Shofar, for chorus and orchestra, and it sets poems by the risingly modish poet Paul Celan. It is programmed, provocatively, on the penultimate night, before Mahler's Resurrection Symphony.
And then there is John Drummond's even more wicked parting shot, a new work by that arch-fiend of British modernists, Sir Harrison Birtwistle, placed smack in the midst of the chauvinistic junketings of the Last Night (16 Sept). It's in the second half, too, so unless BBC1 is very clever (or very insistent), it will have to broadcast it along with the rest of its regular live coverage. Malcolm Arnold's reworking of the Henry Wood Fantasia on British Sea Songs a few years back was controversial enough; what will the Last-Nighters make of Birtwistle's Panic?
Despite the odd, possibly significant, omission here or there, for anyone who isn't terminally incurious, the Proms Centenary offers an intriguing overview. What does it say about the musical state we are in? Well, despite what some neo-phobics may say, we do seem to have arrived at a point where - thankfully - style is no longer the moral issue it was back in the modernist Sixties and Seventies.
Few critics or composers are likely to tick a new piece off for its harmonic, rhythmic or colouristic language per se - not in public, anyway. There is no prevailing standard against which such stylistic features can be evaluated. On the other hand, few would dare to speculate about where new music is headed - in fact, the idea that there is a single entity called "new music" or that it must be "headed" anywhere, seems less tenable than ever.
The composer John Tavener, for one, appears to be saying that we in the West are growing out of the belief that progress is everything. In a recent interview, Tavener quoted a Sufi mystic: "All the doors to Heaven and Hell stand open at the moment, and we can go through whichever we choose." One might add that we are also free to decide which door leads where. The world since the end of the Cold War is a place of frightening uncertainty, but it could also come to be seen as a time of valuable and productive flux. Which composers today, if any, foreshadow the new era to come? This year's Proms season offers as good an opportunity as any to investigate.
The Centenary Proms Season opens on Friday at the Royal Albert Hall, Kensington Gore, London SW7. Advance booking: 0171-589 8212. Proms places: pounds 3 (arena), pounds 2 (gallery) at the door. All concerts are also broadcast on BBC Radio 3Reuse content