There Are two certainties about tomorrow's meeting of Arsenal and Manchester United at Highbury. One is that Sir Alex Ferguson will cry to the gods for a performance that does not mock all his great years as the most successful manager in the history of British football.
The other is that at no stage will Arsenal begin to reproduce the gutter-level behaviour which so disfigured the meaning of their club, and the achievements of their brilliant manager, Arsène Wenger, in the Old Trafford fixture earlier in the season. And it is here that we might indeed find the key to the extraordinary reversal of fortunes experienced by England's greatest football clubs.
Some said that what happened at Old Trafford, when Martin Keown and Lauren and Ashley Cole submerged Ruud van Nistelrooy in their bullying spleen, was relatively trivial, something way down the food chain of football disrepute.
Others said it was an appalling statement about the discipline and demeanour of an otherwise superb team. Wenger, bewilderingly for all his admirers, seemed to take the former view. He gratuitously insulted Van Nistelrooy, and said he would defend his players. The club directors, perhaps led by the traditional voice of the Hill-Wood family, at last reined in their virtuoso manager. They issued a grovelling apology, and said that they would not be a party to any defence of the indefensible. Wenger complied, however reluctantly.
There are no doubt other reasons why Arsenal have maintained such marvellous consistency ever since, but surely it is impossible not to believe that the Old Trafford incident served as the most dramatic warning that an unacceptable point had been reached in the players' conduct on the field. Certainly there is no doubt Arsenal's discipline has sharply improved, and it is one of the oldest truths in the game that a disciplined team is well on the way to being one that wins a lot more often than it loses.
Ferguson's tide of triumph only began to flow relentlessly when he addressed United's own disciplinary problems, and Brian Clough's extraordinary, eccentric winning of two European Cups at Nottingham Forest was underpinned by the terror of his players that they would offend him with any unprofessional behaviour.
Now we look at Arsenal and see a team finally showing the resolve and the composure to make a serious challenge for the European Cup after years of failure so profound that it was plainly eating into their collective psyche. That such a transformation could be worked by a group of players who so recently did such a fine impersonation of a malignant mob is truly remarkable. So, too, is the fact that it is reasonable to presume that United are well capable of ransacking their memories and producing a performance that will rescue at least a little pride - and that it will happen in a game marked by quite impeccable behaviour.