The essence of the European Union and its broad principles are set out in the Treaty on European Union, and not in the first Schengen agreement. However, when they signed it on 14 June 1985, the five founder States stated:
"Aware that the ever closer union of the peoples of the Member States of the European Communities should find its expression in the freedom to cross internal borders for all nationals of the Member States and in the free movement of goods and services"
"Anxious to strengthen the solidarity between their peoples by removing the obstacles to free movement at the common borders between the States ...".
These two sentences encapsulate precisely what the current threats to the agreements and their implementation could mean: the price of reimposing barriers to free movement of people and goods where we had succeeded in getting rid of them will be more than the cost of putting up some new barriers and paying the border guards just so we can have the old days back.
Yes, those were the days, queuing up in your car to go through customs. If you're old enough you might remember how you only really felt you were on holiday when you'd crossed those two barriers. It gave real meaning to the word "abroad".
And then again, what a boon for our logistics companies and, behind them, all their clients who are trying to sell their products or buy their raw materials elsewhere than in their own country. Just like our parents and grandparents, we can again look on the great United States market with a mix of admiration and jealousy. With whom, by the way, we may in the meantime have signed a trade liberalisation agreement. We will see how equally that benefits the two sets of millions of consumers on each side of the Atlantic – one united and one fragmented.
What's more, our businesses have lost that healthy habit of building up national stocks. Now things are too easy, and they don't need to factor in delays any more, they load their stock directly onto the lorries or containers. We'll have to have another look at all that – think "lorry queues at Calais".
In fact, the effects of shutting down Schengen would go much further: if solidarity is strengthened by removing obstacles, then it is bound to be weakened when they are put back. If freedom to cross borders and free movement are the expression of an ever closer union between peoples, then anything that hinders them points to division between peoples.
Not so long ago Europe – the whole continent, not just the EU – was the world champion in walls, with a particularly impermeable "Iron Curtain" that was all the more sinister because trying to cross it cost quite a few "asylum seekers" their lives. In the end, it came down amid universal rejoicing. And if I remember correctly, it was "civil society" that brought it down, the flow of refugees just being too great for it to withstand. Some people are so nostalgic it seems they want to bring it back all along our internal borders.
The European venture is of course a noble, intelligent and open one, because it was borne of the determination of men and women who, in the wake of a devastating war with all the horrible crimes it entailed, worked to ensure that problems would be settled otherwise then by the barrel of a gun. And because as well as peace, it had a strong economic and an embryonic social dimension – the purpose behind the institution of which I am president – it of course acted as a magnet to all those peoples who had not yet joined it.
I think the people of Europe urgently need to mobilise to stop the return of obstacles to free movement for themselves and for goods. We are hearing far too often at the moment from an active minority who are hostile to European integration, and not enough from the majority of people who don't want to lose what they have gained or their freedoms.
Creating obstacles will do nothing to solve the refugee problem, or any other problem. On the contrary, they could herald a "disunity of peoples" that might even threaten peace itself - which is far from the invulnerable heritage our past successes may have led us to believe. The solution lies elsewhere, and the European Union is not the problem – indeed, it is the solution.