The Romans had put an end to the social struggles in the Greek cities and had given an implicit guarantee of survival for the wealthy.

In its 45-page report today, the Congressional Budget Office stopped short of recommending that the implicit guarantee be withdrawn.

The report valued the implicit guarantees enjoyed by the companies at $6.5 billion last year, although this involved no actual outlay of money.

In fact, there seemed to be an assumption that private loans to nearly any government carried an implicit Western guarantee, although none had been promised.

This is partly due to an "implicit guarantee" that the government would not allow such important institutions to fail or default on debt.

A big concern is whether central counterparties could become too important to fail and therefore get an implicit guarantee from governments.

Most important, Fannie Mae's securities come with an implicit guarantee that they are backed by the federal government.

A pegged exchange rate is a form of implicit guarantee, and leads market participants to expect such bailouts.

This should of necessity give rise to a rating without a corresponding implicit guarantee from the EU countries.

"If you want continuous motivation and an energized company, you have to have some implicit guarantee that pink slips are a last resort," he said.