A dual system: Here the drachma and the euro would circulate side-by-side. This has many historical precedents going back centuries. In practice, a dual system is likely to emerge when the Greek government runs out of euros and has to pay its domestic bills in government IOUs.

 The IOUs could at some future date be redeemed in euros, or could be eventually redeemed in drachmas, but they would initially be euro-denominated obligations of the government that would have a lesser value in the public mind than euro notes or coins. This state of affairs could continue for a long time, but there is an economic tendency called Gresham’s Law: ”Bad money chases out good.” Over time, euros would disappear from circulation because people would hoard them as a store of value – and people would spend the government IOUs. De facto, the drachma, whether or not it would so be called, would become the main means of exchange.