European Diary/Denis Staunton: For Valery Giscard d'Estaing, it is "a central innovation" of the new constitution for Europe he helped to draft. To critics of European integration, it is a shameless power grab by EU leaders who want to change the rules that govern Europe without consulting the people.
Whatever you think of it, the passerelle - or pathway - is likely to become one of the most contentious issues in Ireland's referendum on the EU constitution.
The new constitution contains a number of so-called passerelle clauses that would allow EU leaders to agree unanimously to change the way decisions are made at European level.
Policy areas that are now subject to unanimity - with each member state holding a veto - could thus become subject to qualified majority voting.
The passerelle clauses do not apply to decisions with military implications or to the area of defence. And none of the clauses allow EU leaders to give new powers to the EU.
In some policy areas - including social policy, the environment and criminal procedure - the constitution allows EU leaders to abolish the national veto without the approval of national parliaments or the European Parliament.
In most cases, however, any decision to abolish the national veto would require the consent of the European Parliament and could be blocked by any national parliament that objects within six months.
As this newspaper reported last week, the Government has drafted a number of amendments to the Irish Constitution to enable Ireland to ratify the EU constitution. Under the draft amendments, Ireland could only agree to abolishing the national veto in any policy area if both Houses of the Oireachtas approve of the change.
The Government has dropped a plan for a further amendment that would remove the need for a referendum on more far-reaching changes to EU policies.
The passerelle clauses are indeed an important innovation insofar as they introduce the possibility of more flexibility in EU policymaking without the need for formal treaty change.
At present, EU treaties can only be changed after a lengthy Intergovernmental Conference (IGC) followed by ratification in each member state.
If the constitution is approved, some changes that would previously have triggered a referendum in Ireland - such as the scrapping of the national veto in some policy areas - would now be possible with the approval of both Houses of the Oireachtas.
The Oireachtas will gain another important new role in EU policymaking insofar as the new constitution gives national parliaments the right to refer new proposals back to the European Commission if the measures are perceived to intrude unnecessarily into the national sphere.
Because the passerelle clauses cannot confer new powers on the EU, they do not represent a shift of power from the national level to Brussels. The restrictions the Government proposes to place on them means that they represent instead a shift from the people - or that part of the people that votes in referendums - to their elected representatives.
On the face of it, referendums are a more purely democratic way of making decisions than parliamentary approval.
On the other hand, we live in a representative democracy that allows TDs and senators to make many important decisions on our behalf - including on taxation, security and defence.
Despite their democratic character, referendums are sometimes difficult to interpret, and in the case of Ireland's most recent referendums on the EU, it is not clear how much they have contributed to public awareness of European issues.
Indeed, the National Forum on Europe has probably done more to deepen public knowledge of the EU than the antagonistic campaigns that preceded each referendum.
Much of the blame for the inefficacy of referendum campaigns in intensifying popular awareness of the EU lies with the timid approach taken by successive governments.
Too often, they have sought to play down the importance of the changes being proposed, leaving voters confused about how far the process of European integration has progressed.
The debate on the EU constitution leaves less room than before for such an approach, so that campaigners on both sides will be obliged to address the fundamental issues surrounding Ireland's future place in Europe.