The excerpt below is from a keynote address gave in 2000 by "Uncle Milt" (or Milton Friedman as he's more commonly known). With all that is going on in Europe currently, it's not likely the question of whether the Euro is long-term sustainable will go away.
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"The euro is one of the few really new things we’ve had in the world in recent years. Never in history, to my knowledge, has there been a similar case in which you have a single central bank controlling politically independent countries.
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Milton Friedman. Keynote address at "Revisiting the Case for Flexible Exchange Rates" Conference organized by the Bank of Canada, November 2000.
Available at http://www.bankofcanada.ca/wp-content/uploads/2010/08/keynote.pdf.
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"The euro is one of the few really new things we’ve had in the world in recent years. Never in history, to my knowledge, has there been a similar case in which you have a single central bank controlling politically independent countries.
The gold standard was one in which individual countries adhered to a particular commodity—gold—and they were always free to break or to leave it, or to change the rate. Under the euro, that possibility is not there. For a country to break, it really has to break. It has to introduce a brand new currency of its own.
I think the euro is in its honeymoon phase. I hope it succeeds, but I have very low expectations for it. I think that differences are going to accumulate among the various countries and that non-synchronous shocks are going to affect them. Right now, Ireland is a very different state; it needs a very different monetary policy from that of Spain or Italy.
On purely theoretical grounds, it’s hard to believe that it’s going to be a stable system for a long time. On the other hand, new things happen and new developments arise. The one additional factor that has come out that leads me to raise a question about this is the evidence that a single currency—currency unification—tends to very sharply increase the trade among the various political units. If international trade goes up enough, it may reduce some of the harm that comes from the inability of individual countries to adjust to asynchronous shocks. But that’s just a potential scenario.
You know, the various countries in the euro are not a natural currency trading group. They are not a currency area. There is very little mobility of people among the countries. They have extensive controls and regulations and rules, and so they need some kind of an adjustment mechanism to adjust to asynchronous shocks—and the floating exchange rate gave them one. They have no mechanism now.
If we look back at recent history, they’ve tried in the past to have rigid exchange rates, and each time it has broken down. 1992, 1993, you had the crises. Before that, Europe had the snake, and then it broke down into something else. So the verdict isn’t in on the euro. It’s only a year old. Give it time to develop its troubles."
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Milton Friedman. Keynote address at "Revisiting the Case for Flexible Exchange Rates" Conference organized by the Bank of Canada, November 2000.
Available at http://www.bankofcanada.ca/wp-content/uploads/2010/08/keynote.pdf.