One by one, with courtesy and efficiency, Koolhaas bats the questions away. Eventually we come to architectural fashion. He likes to think he is on a different loop from most of us. He tends to support the unfashionable architecture of the immediately preceding generation: in the mid 1970s he was dead keen on the huge areas of council slab blocks outside Amsterdam, for instance, and found beauty in the Berlin Wall. "An obsessive sense of fashion implies a blindness for what is not in fashion," he says. "I've always done the opposite. I've always considered it a provocation to look for value in that which is temporarily obscured."

So, I suggest - are we in for the post-modern revival then? It's a bouncer: just for a second, Koolhaas is thrown off balance. Will he discover the virtues of all those despised 1980s buildings with their cartoon-like historicist motifs? This is not what he meant at all. No avant-garde architect could possibly mean that. He recovers. He does not, after all, predict the future. He laughs. "Time will tell." That's all he will vouchsafe.

Koolhaas is, without doubt, one of the world's most interesting architects. So far, he has mostly avoided formulaic responses. He has stayed on the fashion tightrope for over 20 years. This is because much of his architecture in an implied critique of other architecture. It is interesting as much for what it is not, as for what it is. That, along with his (flatly denied) self-mythologising tendency constitutes his weakness. The new Oporto concert hall, however, shows that he is, after all, only an architect, obsessed with form as all architects are. The Koolhaas cult once seemed a clear case of the Emperor's New Clothes. It is a relief to realise that it was the Emperor's Old Clothes, all along.