Such a visceral dislike can be deconstructed, two teams packed with world-class players compared and analysed, two cities' place in English football's firmament assessed, but in the end it comes down to two numbers: 19-18. Their significance should be immediately apparent to followers of Manchester United and Liverpool.
The Merseysiders' record of 18 league titles has stood since 1990, a year when Sir Alex Ferguson won his first trophy in England in a season featuring calls for his dismissal from some supporters. Two decades on, he stands on the brink of rebranding Manchester United as the most successful club in the history of the English league. Last year's triumph levelled the scores at 18-18. The next has an added importance. Given the sheer longevity required to accomplish it, displacing Liverpool would rank as the Scot's greatest achievement yet.
For a manager who once pronounced his mission was to "knock Liverpool off their f****** perch" and for his Scouser-baiting club captain, Gary Neville, it is personal. For Ferguson, everything is. He was not born and bred into this rivalry, but nonetheless feels it more than many Mancunians. "It's hard to match this game in terms of intensity," he said. "There is hatred in the air. But for us it's about trying to win another championship and leaving a legacy, players who can carry on the tradition of the club."
Liverpool's traditions bring a different meaning at Old Trafford since a statement Rafa Benitez, the Liverpool manager, directed at United 14 months ago. The list of supposed facts that has become known as "Rafa's rant" was directed purely at Ferguson. Since then, United fans have delighted in assertions of superiority, punctuated with the word "fact". But while they have won the war, Liverpool have prospered in the battles. Benitez's men have won the last three meetings dramatically and, in the last two, emphatically. Now their objectives are varied: securing fourth place, halting the United juggernaut and, in protecting their own proud record, enable Arsenal or even Chelsea, scarcely a popular club at Anfield, to finish first.
If feels wrong to demote United versus Liverpool, still the country's marque clash, to secondary importance to the title race, it is a match bursting with subplots that could determine both. The most potent player in the country is a Liverpudlian and he, Wayne Rooney, is United's talisman. Liverpool's homegrown bastion of excellence, Steven Gerrard, is fortunate to be eligible after a forearm smash on Portsmouth's Michael Brown on Monday went unpunished, though not unnoticed by Ferguson.
Gerrard versus Rio Ferdinand is England's latest captain against their official leader. Fernando Torres versus Nemanja Vidic is, for the otherwise fearless Serb, painful. Tormented by the quicksilver Spaniard, he has been dismissed in each of the last three meetings. The 4-1 victory at Old Trafford last season was particularly harrowing for Ferguson. "It's embarrassing to even think about the goals we conceded," he said. "It was terrible to watch it again. The whole thing was ridiculous."
The roll of dishonour included the rest of the United defence that day. In this fixture's past, Javier Mascherano also has a prominent part. And to complete a busy afternoon for referee Howard Webb there is the Neville factor. Brother of the captain of Everton, the United captain has defined himself as the fan on the pitch and has a chant celebrating his hatred of Scousers. A still more decorated veteran, Ryan Giggs, could return for United after a month out with a broken arm. Ferguson must decide, too, whether to recall Paul Scholes and revert from 4-4-2 to 4-3-3.
For Benitez, the choice is between attrition and aggression. He cast caution aside against Portsmouth on Monday, fielding Ryan Babel and Alberto Aquilani in his starting line-up. The solidity Dirk Kuyt and Lucas Leiva offer may get them the vote instead. For a manager who aimed to overhaul United this season, the worst-case scenario is that defeat to them renders him a lame duck. Indeed, the consequences of defeat for Liverpool could be huge, the reward for victory still bigger for United. Liverpool won 2-0 in October, 4-1 last March, 2-1 in September 2008. While it sounds more like a scoreline in rugby than football, the issue now is whether it will be 19-18 in May.
firstname.lastname@example.org Manchester United v Liverpool, 5.30pm, Showsports 1 & 2