EU members can be forced to leave the euro or the EU.
Countries can leave the EU voluntarily, but can't be kicked out. Strictly speaking, there's no legal mechanism for a country to either leave or be ejected from the euro.
Yesterday's newspaper headlines on the Greek crisis are a study in contrasts.
The Guardian and Telegraph reported European politicians as saying that Greece's membership of the euro is at stake in this weekend's referendum, whereas the Times had the story as "Leaders warn Greece will leave EU if it votes no".
As we in the UK should know, being in the euro and being in the EU aren't the same thing. You can leave the single currency without leaving the EU. So when people talk about 'Grexit', which do they mean?
From a strictly legal perspective, Greece can't be involuntarily ejected from euro or Union.
That's a pretty certain bet in practice as well when it comes to EU membership.
There is a mechanism for voluntary departure, which is what Britain would activate were we to vote to leave in our own referendum. (Don't be fooled by viral posts or emails saying that other EU countries can vote to block us from leaving; they absolutely can't.)
But the EU Treaties don't talk about involuntary departure, as the experts at EU Law Analysis point out. The most that's provided for is suspension (in circumstances not relevant to Greece's current situation).
Countries can't formally be kicked out of the euro either; nor are they supposed to leave on their own initiative:
"legally speaking, Greece can't directly jump or be pushed from the single currency".
There's a good practical reason for this: confidence in the permanent nature of the euro might have been undermined if there had been a mechanism for countries to leave it.
But the practicalities of high politics and finance may well overtake the formal position in the next few days. We're not suggesting that the legalities are the last word.