On paper, it's easy.

On paper, it's Ireland. They are the reigning champions, they have just risen to third in the world, they have the hottest coach on the planet and they won nine of their 10 games last year. They are strong in every position and they have even managed to cope with the loss of Brian O'Driscoll. There isn't an argument against them.

But then, it was meant to be easy last year. Twelve months ago, the professional chinstrokers were backing Wales, champions in the two preceding seasons and apparently purring along quite nicely. Over the previous 10 months, coach Warren Gatland had masterminded the destruction of England in a momentous title decider and had then led the Lions to a series victory in Australia.

Go back another year still and you find that the runes were saying England. Stuart Lancaster had made solid progress in his first year in charge, ending it on a high as his side hammered the All Blacks 38-21 at Twickenham. It was going to be easy then as well.

But it never is. You can't ignore form completely in the Six Nations, but there are too many other factors swirling around in this heady brew of a championship. There are the injury lists - crippling for England, almost non-existent for Ireland - and there are the issues of home advantage and order of play. No disrespect to Wales, but would they have smashed England 30-3 two years ago had the sides met at Twickenham at the start of the tournament rather than in Cardiff at the end?

That match will be recalled and revisited endlessly until those two sides finally get the 2015 championship underway at the Millennium Stadium on Friday evening. It is an explosive beginning - but only that. In quick succession over the following 24 hours we have the tumultuous and emotionally-charged clash of France and Scotland in Paris, the first major event the city has hosted since the Charlie Hebdo atrocities, and Ireland's first outing in the gladiatorial surroundings of Rome's Stadio Olimpico. If Ireland slip up there, as they did on their last visit, then all bets are off.

It is hard to see that happening, though. Joe Schmidt is too thorough, too much of a detail guy, to allow his Ireland side to lapse into their old habit of throwing in the occasional wretched performance. The indications this season are that the side that beats Ireland - if such a side exists - will do so on their own merits, not on the strength of their opponents' lack of concentration.

England will have that opportunity in Dublin on the first day of next month. By then we will know if Lancaster's World Cup plans are on track, whether they are surging on and laying waste to all-comers as Clive Woodward's England did in 2003, or whether they are already fighting a desperate rearguard action. No coach is facing a bigger year than Lancaster. It could just as easily end with a P45 as a knighthood.

But what of Scotland? That opening engagement in the Stade de France is a ferocious start, but if they can emerge from it with bodies intact and a degree of self-esteem then we will have a much better idea of what they can do when they take on Wales at BT Murrayfield the following weekend. Coach Vern Cotter may be a relative newcomer at international level, but he has impressed in his first eight months in the job and he heads to Paris with the advantage of deep knowledge of the French side.

Cotter has made it his business to get to the heart of Scottish rugby, to unravel its DNA. Coaches mostly prattle on in the language of pseudo-scientific mumbo-jumbo, but he has been happy to look to the past for the cues that will make his side play well. He has settled on the kind of game Jim Telfer demanded in his spells as coach: fast and ruinous forward play; backs who look for space; accuracy in everything the players do.

Greig Laidlaw is certainly buying into it as well. The little scrum-half and captain is as down-to-earth about rugby and life as the new coach, and Cotter unquestionably sees value in the fact that he has his feet in the same Jedburgh soil that produced Roy Laidlaw and Gary Armstrong.

Armstrong was the captain when Scotland last won in Paris, 16 years ago, and Laidlaw flushes with pride at the mention of that occasion. "I remember watching it on television," he smiled. "It was a great day for Scotland. It was a very Scottish performance that day, with pace, good rucking and they moved the ball quickly.

"If we are to win will have to emulate that this weekend. Gary had a huge influence on me. He was a great player and a great man. It was brilliant for me to see someone like him from the small town, where I grew up as well. He was a big part of that team and he was a great leader."

Laidlaw will have to grow into one as well. His first efforts at captaining his country were not wholly convincing, but he has grown into the responsibility. His autumn performance against Argentina was close to his best in a Scotland shirt as he played with renewed vigour and sharpness and appetite.

Those qualities ran through the whole team in those November games, but then autumn optimism has been a familiar theme of recent seasons. Time and again, though, the spring sunshine has had a baleful quality, with Scotland's shortcomings exposed in the subsequent Six Nations.

They will be forgiven a defeat in Paris, but not the sort of weak performance they put in against Ireland in their first game of the championship last season (and certainly not the feeble effort of their second game, against England). For Scotland, the key to every successful Five or Six Nations campaign has been to pick up momentum. What they must not do in France is hit the buffers and leave themselves with a rebuilding job.

The signs to date are promising, but they can also be misleading. Cotter has yet to claim one of the big scalps of rugby, yet to lead Scotland to a victory against a team placed higher in the world rankings - as a ll but one of their Six Nations opponents now are.

He has a squad and a gameplan that can make things happen. But for the moment it's only there on paper.