One winter evening in Dublin a couple of years ago, a group of philosophy undergraduates gathered in a lecture hall at Trinity College to listen to a talk by a man whose achievements in a field generally considered non-academic have been so great he gets asked advice on leadership by would-be prime ministers.
Sir Alex Ferguson told the students that mastery of his job, that of a football club manager, depended above all on two things. He listed them: "Power, and control."
One, logically, leads to another, and control, Ferguson suggested to an audience mostly of people of a similar age - though a lower personal income to many of the footballers over whom Ferguson wields power - had become more difficult to achieve with each passing year.
"If I lose control of these multimillionaires in the Manchester United dressing-room, then I'm dead. So I never lose control. If anyone steps out of my control, that's them dead."
Stark words, and a studied challenge to anybody who wants to take on Ferguson.
The list of players who have stepped too far out of Ferguson's control and suffered for it is quite familiar: Paul Ince, David Beckham, Jaap Stam, Ruud van Nistelrooy; they left Manchester United having contributed considerably to the successes of the manager's very long reign. But they displeased him and so they departed.
To that list you could perhaps add the name of Carlos Tevez, just as a footnote. Tevez had been recruited at Ferguson's behest, arrived at United under an unusual contractual situation, played well for United and gained popularity with the fans.
He was allowed to leave because United put a different financial valuation on him than he and his advisers had done and because Ferguson eventually took a similar view to the club.
Tevez then joined Manchester City. The rest is history.
The point here is that Tevez's City career is not, to borrow Ferguson's term "dead", and the fact he may play in another Manchester derby - and he has already animated several of them, in red and in blue - seems to indicate a great deal about the differences between Ferguson, 70, and Roberto Mancini, 47, in matters of power and control.
Tevez challenged Mancini's power as manager when he refused to bow to his instructions during a Champions League match in Munich.
Mancini's way of taking control after an individual's explicit act of rebellion was to exclude him from his future plans.
Ferguson at the time backed Mancini, emphasising the importance of managerial authority.
But Mancini's position regarding Tevez would soften. Tevez did not leave the club in January, as many executives at City would have liked.
He has since been recalled to the side, and had the odd moment of positive impact on the title run-in.
Would Tevez, disobeying Ferguson with television cameras as witness - as Tevez did with Mancini in Bavaria - ever have played under the Scottish manager again? Who knows?
One of Ferguson's great skills as a man-manager is to set out a firm set of principles in public and then apply flexibility if it means getting the most from an individual.
He has made plenty of errors of judgement in his selection of footballers in the transfer market over more than 25 years in charge of United, but he has not shied away from hiring a gifted maverick and indulging him from time to time.
Would Ferguson have signed Mario Balotelli, knowing as much as Mancini, who had worked with the teenaged Balotelli at Inter Milan, knew about the troublesome Italian striker? Well, Ferguson did sign Eric Cantona.
On the face of it, the manager of City and the manager of United can appear polar opposites.
As a player, Mancini was an elegant, dashing inside forward; Ferguson was a rough-hewn target man. Mancini, as the former Inter striker Zlatan Ibrahimovic noted, has a streak of personal vanity, can look "a bit of a Fancy Dan, nice suits and so on".
Ferguson, as a recent biographer, Patrick Barclay, wrote, has "a hairstyle that remains as it was in his playing days".
A former Ferguson player once coined the phrase "hairdryer" to describe the hot, close up to the face shouting technique by which the United manager expresses anger; those who complain about Mancini's interpersonal style more often describe him as subzero cool, unapproachable.
Yet they also have much in common and, over the last two years, Ferguson has come to see in the Italian manager of his so-called "noisy neighbours" a drive, a single-mindedness and a craftiness in achieving power and control that he must recognise rather well.
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