This means that, at the horizontal level between euro area members, there is an obligation to respect what Isaiah Berlin called the concept of “negative liberty” – to conduct economic policies individually within limits that do not impinge upon the liberty of the other countries.
There is another obligation to establish institutions and instruments that preserve the stability of the system taken as a whole. This is an implicit social contract which, before the crisis, was believed to be largely self-enforcing – if not by countries themselves, then by the discipline of financial markets. That this assumption was misplaced is now part of history.