Everything tactical in football is relative. There are few absolutes; everything has meaning and relevance only in relation to everything else. The question "What's the best formation?" is nonsensical because it depends on so many subsidiary questions: who are my players? How fit are they? How confident are they? How motivated are they? What are they used to doing? What result do we need from this game? Are we home or away? What is the weather like? What is the pitch like? Who are the opposition? How do they play? What shape do they play? How are their form and fitness? Even if a manager can accurately assess all of that, it may still be that after 10 minutes it becomes apparent that he needs to tweak something because of a player, whether on his side or the opponent's, suddenly having a great game or an appalling game.

Yet trends develop. Certain formations become modish. Often, as with the long-standing reliance on 4-4-2 in Britain, it's to do with how football is coached at youth level. Sometimes it's because a successful team makes a particular way of playing popular – 4-4-2, for instance, first came into vogue because of England's success at the 1966 World Cup. And sometimes formations disappear because, in the great game of scissors-paper-stone that football tactics often become, the fashionable way of playing is particularly effective against it.

Three years ago, playing three at the back had all but disappeared. It had died away in the late 50s and 60s as the W-M was superseded by a back four, and re-emerged in the mid-80s, in slightly different forms, with Carlos Bilardo's Argentina, Sepp Piontek's Denmark, Franz Beckenbauer's West Germany and Ciro Blazevic's Dinamo Zagreb. The logic was simple: a libero flanked by two man-markers who picked up the opposing centre-forwards, wing-backs to drive the opposing wide men back and, against a 4-4-2, an extra man in midfield to help control possession (it was this approach, rather than the use of a back three per se, that Johan Cruyff described as being the "death of football"). The problem came as teams stopped playing two centre-forwards. Leave a libero and two markers against one striker and that means one of the markers is redundant (and, as a marker, probably not that adept at stepping into midfield), which in turns means a side will be a player short elsewhere on the pitch.

Yet three at the back has started to make a comeback. It began in Italy, with Udinese and Napoli. At Barcelona, the first and most successful stage of Pep Guardiola's season-long charge backwards through the evolution of tactics was a back three. Then Wigan Athletic started doing it. Now Manchester City have joined in. In fact, in the top divisions of Europe's top five leagues over the weekend, 12 teams used the shape (eight in Italy, two in England, one in Spain, one in France and none in Germany). Three at the back is back.

The difficulty of playing with three at the back against a lone striker has not gone away, of course. But what has emerged over the past few seasons is that there are specific circumstances in which the benefits of the shape outweigh that negative. Most obvious, for teams that sit deep and seek only to defend, having two spare men at the back (particularly if the marking is zonal rather than man-to-man) is actually a major advantage. Perhaps because of the extraordinary control of the ball achieved by Barcelona and Spain, it now seems more acceptable for games – in the minds of the team doing defending if nothing else – to take place only in one half, for one team to sit extremely deep and look to absorb pressure with only the occasional breakaway or set play. Internazionale's performance at the Camp Nou in the second leg of the Champions League semi-final in 2010 opened a new vista of defensive possibility.

That was certainly the logic Bordeaux used away to Paris Saint-Germain on Sunday, holding them to a 0-0 draw with an extremely defensive 3-3-3-1: Carlos Henrique, Ludovic Sané and Michaël Ciani across the back with Henri Saivet and Ludovic Obraniak playing almost alongside the holder Landry Nguemo, so the shape was often a 5-3-1-1. That's three draws in a row for PSG and, as Philippe Auclair pointed out, it's not that teams have found a recipe for upsetting PSG, it's that everything that has been tried against them has unsettled them: Lorient counterattacked, Ajaccio sat back and sprang forward in controlled bursts of pressing; Bordeaux just stayed exceptionally deep.

In Italy, the attraction seems cultural. I discussed the issue in some detail here in February, but essentially there is a cultural urge to pack the centre, which is why two years ago the default formation was 4-3-1-2 with very little width. A back three offers a way of gaining attacking width (see, for example, Stephan Lichtsteiner getting forward to score Juventus's opener against Parma on Saturday) while still being able to retain the number of bodies in the centre that Italian football seems to need to feel comfortable. It was also notable at the weekend that six of the eight sides using a back three were playing each other: Fiorentina against Udinese, Juventus against Parma and Palermo against Napoli (the other two were Bologna using a defensive back three away to Chievo and Siena playing a 3-5-2 against Torino's narrow 4-4-2). It may be that there was some matching of shapes going on, teams adopting a back three to play against a back three.

The third group that may be attracted to a back three is those following the Bielsa protocol. Marcelo Bielsa's philosophy is radical – too radical, sadly, for most players, as Athletic Bilbao seem to be finding out (he may be the greatest theorist in football today, but the practicality of dealing with players who persist in being human undermines his coaching). For him defending is less about marking or reacting to opponents than about pressing to regain possession. He needs to be able to get players high up the field quickly, partly to attack an opponent in possession and partly to offer passing options when possession is regained. That is the logic Barcelona followed last season.

Quite what advantage Manchester City see in using a back three is far from clear. They played with a back three against Chelsea in the Community Shield and then again against Liverpool on Sunday. "We went to it last year a little bit to close games off, but what the manager has tried to work on all pre-season is the ability to be able to go to a back three if we want to, and be more offensive than defensive with it," the assistant manager, David Platt, explained in a piece with the Manchester Evening News after the 3-2 win over Chelsea. "The problem is that when you give the ball away you are more susceptible to a counterattack, and we did that for both goals against Chelsea.

"Robbie [Mancini] wanted to have a go at it this season, and we had discussions about it. Last year we flicked into a three at times, but we did it tactically, such as when we were 2-0 up with 20 minutes to go and someone puts a big striker on, to snuff out the space. Then it was done more from a defensive point of view in the last 15 or 20 minutes when teams were throwing everything, and the kitchen sink, at us. To add that other string to the bow, we had to have a good look at it from more of an offensive point of view, where we would have the wide centre-halves coming out and playing with the ball rather than staying narrow, and we are getting the wing-backs high."

The attacking possibilities were apparent at times in the Community Shield, most notably when the left wing-back Aleksandar Kolarov got forward to cross for Samir Nasri to score City's third. Defensively, City were rather less comfortable. Against Liverpool, the problems were more pronounced (and, of course, although City ended up winning the Community Shield relatively comfortably, they were trailing when Branislav Ivanovic was sent off).

The problem was the classic one of having three central defenders line up against a single central striker. With Raheem Sterling and Fabio Borini both threatening, neither City wing-back could get forward, and that meant Liverpool, with a midfield three plus two full-backs (although both were perhaps more cautious than they needed to be) able to push on in the absence of any City threat from wide, were able to dominate City's midfield two of Yaya Touré and Nigel de Jong plus Nasri dropping back. City in the end were extremely fortunate to take a point.

So why did City use the back three? From what Platt said it would be to make City more like Barça, to drive the game higher up the pitch.

But if that was the aim, then why start with a midfield four as functional as James Milner, De Jong, Touré and Kolarov? That's not a four geared to ball retention. But equally it seems inconceivable that City, facing a Liverpool side that had lost 3-0 to West Brom on the opening day, would have seen the need to go in with additional defensive cover – and the way they started the game certainly wasn't defensive.

The lazy analysis of Mancini is to say that he's over-cautious because he's Italian, a weary stereotyping that's so generalised as to be meaningless. Where Mancini does seem to stay true to the traditions of the Italian game, though, is in his distrust of wingers (which you suspect Adam Johnson's fitful form only intensified). His sides, both at Inter and City, have always been narrow: playing a 3-4-1-2 allows him to have players overlap, as Kolarov did against Chelsea, while, in theory, retaining solidity. The problem comes against teams with genuine width such as that Liverpool demonstrated on Sunday.

But there are wider problems. While it's always useful to have an extra tactical option, it's hard to see how it's possible for City, given personnel, to play a 3-4-3 or 3-4-1-2 without it becoming a broken team: a back three, two wing-backs, a holder (or two) and poor Yaya Touré slogging up and down to connect the back six to the front three. For one thing, that would seem to make it very difficult to fit Nasri and Silva into the same lineup, and for another that would seem to increase the reliance on Touré, which it must be one of the aims of this season to reduce. There's nothing wrong, as such, with being a broken team, but it's a reactive way of playing: surely the richest team in football, a team that could be to this generation what Real Madrid was in the 50s, should be pro-active in approach, should be looking to produce a cohesive style of football that seeks to dominate games?

Even if City's approach is puzzling, though, three at the back has re-established itself. Wigan Athletic's use of it is fascinating, particularly given how, this season, it has often morphed into a back four with Maynor Figueroa falling back in to a more orthodox left-back position at times. With Shaun Maloney dropping deep and Arouna Koné clearly operating behind Franco Di Santo, the system in Saturday's win against Southampton was a base 3-4-2-1 that at times looked like a 3-4-3 and at times like a 4-4-1-1. For Roberto Martínez, the back three seems a way of enhancing flexibility without sacrificing too much solidity: he has a back three and a front one and six players who adjust as required. In that, they're not dissimilar in approach to Napoli and, like Napoli, it's an approach that seems specific to that relatively small group of players. Wigan are unlikely to rotate too much this season.

Every generation feels as though it is living at the end of history.

It's very hard to imagine what will come next. How could there be anything new on football? How can it develop tactically? But evolution isn't necessarily forward. Perhaps there are no great tactical revolutions to come; probably our globalised, perpetually analysed world militates against them. But there is still plenty of life in old ideas, still plenty of ways to reinterpret that with which we are already familiar.