After the administration of rugby union was formalised in the 1870s, it was officially designated throughout the world as an amateur game - and that meant not just the players, but all the technical and administrative jobs that made the game possible. Since Sunday the new designation is "open", which means that anyone involved in rugby in any capacity at any level may henceforth be paid whatever the market-rate turns out to be.
Now, though, comes the hard part: to work out how the new professional game will operate in practice and to sell the notion to the mass of rugby union's global membership, to whom amateurism is more a practical necessity than an article of faith.
Because, apart from the well-heeled handful among the 67 countries that form the membership of the IRFB, rugby union's world governing body, most member countries have hardly any money to provide pitches, let alone pay the players.
Try, for example, telling South African rugby's new constituency in the townships that they are now eligible to be paid for doing what was until recently denied to them. There would be an incredulous response. And one can well imagine the largesse that the rugby unions of Moldova and Tahiti, the board's newest recruits, would be able to bestow on their star performers.
The uncomfortable truth is that the IRFB's decision poses as many questions as it answers, even if in such rugby-oriented places as (non-township) South Africa and New Zealand it simply legitimises what has long since been custom and practice. Rugby union has come late to professionalism, compared with football and cricket anyway, and does not quite know where to go from here.
Yet you could argue that the Paris announcement was no more than the formal acceptance of a fait accompli. In other words, if the governing body had not acted, individual rugby unions would have gone ahead anyway.
The pressure of late has been intense. Over the past month or two, Kerry Packer, the Australian media mogul, has tried to establish an alternative rugby union - the World Rugby Championship - by buying up the best players. This threat - now collapsed - led unions around the world to conclude ever-more expensive deals in an effort to hold on to their players' services. Previously, they were entitled to receive payment for more or less anything - promotional work, appearances, speeches and the like - as long as it occurred off the field. In South Africa, the going rate turned out to be pounds 100,000 per player per annum; in England, pounds 40,000.
This, remember, was before the game had gone professional. The English pounds 40,000, to be raised mainly through sponsorship, is the minimum now guaranteed by the RFU to any individual who takes part in all of England's matches during the next year. This is separate from and in addition to contracts that players will be signing with their clubs.
The practicalities of this hazy, two-tiered system will give the administrators infinitely more grief than was ever caused by the protracted and agonised debate they have just had.
In opening up the earning opportunities of anyone connected with the game, not just leading players or even players generally, the IRFB has in effect told the legion of unpaid helpers who devote their attention to rugby union because they love the game that their services - the humblest turnstile attendant every bit as much as the captain of England - have a price.
It was always Dudley Wood's dire warning while he was secretary of England's Rugby Football Union (RFU) that as soon as players were permitted to be paid, there would be an exodus of people who in a professional world would no longer be motivated to give freely of their time. This issue was not addressed by the IRFB and has not yet been addressed by the RFU, but it is already on the minds of the clubs that will be affected.
Take Bath, the English cup-holders. They will have to find as much as pounds 700,000 on top of their regular income - an annual commitment that had simply not existed before. Even to a club of Bath's elevated stature, this is a mind-boggling sum. Last season, when they beat the Wasps, the London club, in the cup final and were runners-up to Leicester in the league, they made a profit of pounds 78,664, and there have been recent, amateur years when they have even made a loss.
The IRFB council will meet again in Tokyo at the end of September and by then it intends to have in place regulations governing transfers between clubs and countries, and which will seek to protect the mass of weaker, impecunious countries whose best players could simply emigrate to Australia or New Zealand and, after a few years, be eligible to play for that country instead.
Without stringent rules, which in any event would probably lend themselves to restraint-of-trade legal actions, the board's best intentions could well turn out to be unviable. Even here in the British Isles there is the obvious possibility of, say, an aspiring Welsh player preferring the greater riches on offer across Offa's Dyke. Most Welsh people have some sort of English connection, after all, and if they did not they could make one up.
Then there is the relationship between the English union and its senior clubs. In Paris, Tony Hallett, who succeeded Wood as RFU secretary last month (and could be excused for now wishing he had stayed in the Navy), speculated that a two or three-year moratorium on clubs' paying their players might be required to prevent bankruptcies, but of equal significance is that the top players will now be serving two masters. The greater a player's contractual commitment to England, the greater the impact on the clubs, and therefore the potential for strife. In other words, the more often he trains or plays for England, the less often he will be able to train or play for the club.
William Webb Ellis, who started the game when he first ran with the ball at Rugby School in 1823, must be turning in his grave.