Today three million Irish voters decide if they want Ireland to participate fully in an improved European Union, or if they want the EU to stagnate.
If they approve the Lisbon Treaty by answering Yes, the enlarged European Union will be able to work a little bit better to promote the values and interests of its 500 million citizens. Openness, democratic scrutiny and EU action will improve to a degree, helping the union to tackle the great challenges of our times in a more coherent manner.
If the Irish answer No, the 26 national parliaments and governments who have approved the Treaty of Lisbon will see their hopes for a modernised EU dashed.
The immediate choice is between the Treaty of Lisbon and the Treaty of Nice.
People are often afraid of change, but in this case the change option is the safer one:
We know the limits of the incremental amendments unanimously agreed between the EU member states. Under the Lisbon Treaty the policies would be made together, by all the member states and within the EU institutions (Council, European Parliament and Commission).
There are no choices free from implications.
We know less about how the pressures for change erupt, if the Treaty of Nice remains the foundation. In principle, a more effective and more democratic union could be envisioned, between a smaller number of member states.
Groups of member states might opt for enhanced cooperation under the old Treaty of Nice, which would establish new cores, still nominally within the EU framework.
Some member states might choose to initiate deeper cooperation outside the EU institutions, on an intergovernmental basis, with a lead role for a few big states, less parliamentary scrutiny and limited openness.
A reticent Ireland, but also positive smaller member states as well as EU citizens would be marginalised. Some big EU states would take the lead and the possible benefits would accrue unevenly across a European Union still in existence, but becoming more of an empty shell.
Do we have to study the implications of a No vote more closely?
I hope not, but if Ireland turns down the Lisbon Treaty, a period of soul-searching will begin, not only for Ireland, but for all the EU members. Then it will not be a question if the dog barks, but how it bites.
I have to admit that I am worried at the prospects.