Article 50 is fast-becoming the most quoted but least read legal provision in the contemporary world. It is also one of the most controversial but least understood provisions. It is being cited by many but read by few. Triggering it is seen as a day of hope or a day of doom depending on one's perspective.

There is an enormous focus on when it will be "triggered" as if that alone will solve or cause problems. In fact, its triggering will simply be one moment (and, even then, a potentially anti-climactic moment) in a potentially long process.

Article 50 permits withdrawal by a Member State from the EU. There was no explicit withdrawal provision until this article was inserted into EU law by the Treaty of Lisbon on December 1, 2009.

The provision is ambiguous, incomplete and awkward to apply - it is not meant to be invoked or applied easily. But how will this provision operate?

International law generally has limited precedent of significant states withdrawing from major international organisations. The UK's withdrawal from the EU would be the most significant ever given the scale of the UK and the EU.

Even the United Nations Charter has no explicit provision to allow withdrawal. Despite Indonesia purporting in 1965 to withdraw and communicating its intention to do, when the country changed its mind, the UN and Indonesia moved on, almost pretending that the incident ever occurred.

A critical issue now is whether serving Article 50 is irreversible. It is significant not least because it could take years for its effects to materialise and there could be, during that timeframe, circumstances which would trigger a rethink.

Many assume that once Article 50 is triggered, it's a trip to Mars, not to the Moon - it would be long, you don't return and you could even be burned up on arrival. Their arguments are straightforward. The provision does not provide for the notice to be withdrawn. It is too serious a matter for flip-flopping. The provision is solemn and should not be used as a bargaining tactic to get a better deal.

However, could the UK withdraw the Article 50 notice? It is submitted that it is legally possible. Politically, it would probably require another referendum in the UK but, legally, there are reasons why it is reversible.

Often in the EU, the law follows the politics: if Member States want to keep the UK in, and the latter withdraws the Article 50 notice, then in all probability the law will be interpreted or, if needed, rewritten to accommodate that outcome.

Triggering Article 50 is a unilateral act by the relevant state and is not dependent on agreement by other states other than to agree the withdrawal agreement. If the putative withdrawing state triggers Article 50 then the other states have to accept it provided the notice is served validly and in accordance with the state's internal constitutional requirements. Other states may not veto either its serving or its withdrawal.

Importantly, Article 50 refers to the Member State announcing its "intention" to leave - this is not a binding irrevocable commitment. Sovereignty theory supports withdrawal. States which have joined the EU may decide to remain or leave. It is a sovereign unilateral decision and the only exception is where the expulsion provision applies which is not an issue here. There is national case law in Germany and the Czech Republic for the right of unilateral withdrawal.

Practice in comparable areas supports withdrawal. There is ample precedent that States have signed up to positions in the EU and then reversed those positions. Norway, for example, signed the Treaty of Accession in 1972 to join the EEEC along with Denmark, Ireland and the UK but changed its mind after a referendum; no one could force Norway to join and the EU even entertained a subsequent application by Norway to join later which again did not proceed.

If a state had triggered the notice but maintaining it was no longer in accordance with the state's "constitutional requirements" then presumably the triggering is no longer valid.

Ireland and Denmark have voted to reject ratification of some EU treaties only to later change their mind in referenda. No one insisted, like a quiz master, "we are sorry, we have to accept your first answer".

More importantly, Article 50 does not trigger withdrawal in its own right. Article 50 is just a procedural enabling provision and it only has effect if no agreement is reached within the time limits specified in the article. There has to be a withdrawal agreement which is what really matters and that would require agreement and even ratification.

There is no guarantee that the UK notice will be withdrawn and no preference is being expressed here as to whether it should be withdrawn but it is clear that, as a matter of law, the balance of the argument favours the argument that an Article 50 notice may be withdrawn.

So there is a need for politicians, business executives and all concerned not to freeze everything during the Article 50 process (life must go on) and also not to assume that there can be only one outcome (Brexit). It is best to plan for Brexit but contemplate the possibility of an alternative. Given the timeline involved - three years or more - anything can happen.

But don't pin too many hopes on a reversal without realising that to reverse the decision on June 23, there would have to be difficult dark days (such as a recession, a crisis or a fundamental shift of views by all or many of the parties) but stranger things have happened.

The world is slowly learning it is much easier to say "Brexit means Brexit" than to win the prize for completing, in ten words or less, the slogan: "Brexit means....." But it is also reasonably clear that one can now say with some degree of confidence that "Brexit does not have to be forever".

This article first featured in the Irish Independent on Friday 16 September.