He had his beliefs and principles and he knew exactly what kind of football he wanted his teams to play on a football pitch but he wasn't as dogmatic as some think. He wouldn't have maintained at the top of the game for thirty years, if he couldn't evolve and adapt to the changes of modern football. It's true that he preferred a more direct approach, he set up his teams to either exploit the spaces behind the opposition defenses with raw pace or use overloads and quick switch plays in the final third to open spaces on the wings. But he didn't always deploy two banks of four and two out and out forwards on the pitch in every single game throughout his career.
It's true that his first United sides, up until the Treble, used the "British 4-4-2" which focused on pacey wingers and counter attacking tactics as their primary system. We had options like Giggs, Sharpe and Kanchelskis on the wings, players who not only were pacey but most importantly could finish moves and create chances while running with the ball. But the tactics weren't rigid, Ferguson was one of the first managers to experiment with inverted wingers (both Sharpe and Giggs were used on the right wing), he often used one forward (or sometimes a winger) a bit deeper in order to disrupt the opposition's deep lying play maker, he took the best out of Cantona by giving him free license to influence our game, he even used a forward like McClair in the midfield in order to maximize our attacking options. Sometimes it looked like a 4-4-2, some others like a 4-4-1-1 and occasionally like a 4-2-3-1.
The first time he decided to move away from this 4-4-2 (or 4-4-1-1) was when he signed Veron back in the summer of 2001. The reasons for that change have been discussed in many threads on this forum. There was a sense that, despite the 1999 season, United were under achieving in Europe. The direct, high tempo approach wasn't fruitful against teams like Bayern Munich or Real Madrid which could match or surpass our quality on the pitch and hit us effectively on the counter. There was also a turn towards tactics which favored a three man midfield that created numerical advantage in the central areas against the 4-4-2. The class of '92 reached its peak from 1999 to 2001 but in the early years of the United-Arsenal rivalry, since Wenger implemented his 4-2-3-1, Arsenal had the upper hand whenever the two teams met. Most people remember Giggsy's wonder goal in the FA Cup replay or the 6-1 (against a rather weak Arsenal side that day) but these are two of our three wins (the third was at Highbury in 2001 with Keane's double) in 11 games against Arsenal from 1998 to 2001.
What hasn't been discussed thoroughly though is the boldness of Ferguson's decision. It takes guts to break up the midfield of Beckham-Keane-Scholes-Giggs, a midfield that had dominated the PL and had won three consecutive league titles. The basic idea was that Veron would operate as a deep lying play maker and Scholes would play off RvP and become a third midfielder whenever that was necessary. The results were catastrophic in England. Arsenal walked the league and United finished third for the first time since 1991-92. Strangely enough that team almost made it to the CL final that season. Next season United won the PL and performed much better (15 wins and only 3 draws in the last 18 league games), Scholes had one of the best seasons of his entire career in his new role.
Next season Veron was sold to Chelsea but Ferguson didn't gave up on his experiments. In 2003-04 Phil Neville was often used next to Keane in the midfield and when Rooney arrived to OT in 2005, he and Giggs often drifted infield with Scholes dropping deeper in what could be described as a very loose 4-3-3.
The introduction of Carrick in 2006-07 brought the tactics with the "two pivots" in the midfield. This was also a rather bold decision since Carrick was signed to replace a DM like Keane. Lots of people questioned Ferguson's decision back then too but again Sir Alex proved everyone wrong. Carrick was the perfect man to shield the back four giving his midfield partner the opportunity to create while Rooney-Tevez-Park were constantly providing tireless runs up and down the pitch giving the opportunity to Ronaldo and Giggs to stay in more advanced positions. In 2008 and 2009 the shape was somewhere between 4-4-2ish and 4-3-3ish formations with the utilization of Park, Tevez and Rooney proving Ferguson a mastermind in defensive wide attackers and defensive forwards. I believe that during that period (until Pep's Barca emerged) Fergie's tactics became dominant in modern football. United remained unbeaten in Europe for two whole seasons, minus one game of course.
The defeat in the 2009 CL final and the loss of Ronaldo brought a change towards more traditional 4-4-2 (or 4-4-1-1) tactics. The logic with the two pivots in the midfield didn't change but the space the CMs had to cover was much bigger because neither Valencia nor Young could drift infield, get on the ball in between the lines and make things happen. This caused a series of problems in the central areas but the team was successful again. And again it was because of Ferguson's ability to adapt. Especially in his last season, when he received lots of criticism for his tactical choices, we saw full backs operating in more advanced areas and becoming attacking threats (which nowadays is used a lot by many managers), we saw the diamond (away at Newcastle for example), a team that defended in a very narrow shape to compensate for the lack of a ball winning midfielder and lots of other little details that made the difference.
The term tactical dinosaur can only be valid if we're only talking about managers who brought something new to the game. But these managers are very rare to find and they're not always successful (take Bielsa for instance).
