The phrase "a firm guarantee" is correct and usable in written English.
It can be used when you want to emphasize the strength or reliability of a promise or assurance.
Example: "The company offers a firm guarantee that all products will be delivered on time."
Alternatives: "a solid assurance" or "a strong promise."
His requests to the Swedish government for a firm guarantee of his safety have been declined.
It would be "very silly" making a firm guarantee, he said.
We reply, "Give us a firm guarantee, a promise that the Americans will not attack Cuba".
"Until unification is actually fully achieved and a firm guarantee of peace is arranged, we cannot afford to relax," South Korea's leader said in a televised speech.
"Will you offer a firm guarantee to head teachers and parents that their child's primary school will not be forced to become an academy on the basis of these compromised tests?" Powell wrote.
Compared with the alternative of coercive sanctions, which are unlikely to bully Iran into submission, this proposal has the distinct advantage of providing a firm guarantee of Iran's peaceful nuclear activity, particularly if coupled with security guarantees for Iran.
After indulging the thoughts and opinions of anyone who was "just like me," it seems that people are now looking for a firmer guarantee of clarity, objectivity and accuracy.
However, the FBU now says the government and fire employers have failed to offer any firm guarantees on jobs or pensions.
Without the firm guarantee of such a trade-off, it is difficult to foresee a meaningful breakthrough in Baghdad.
In 1990, NATO General Secretary Manfred Woerner said, "The fact that we are ready not to place a NATO army outside of German territory gives the Soviet Union a firm security guarantee".
Most of the Iran analysts, according to Pillar, believed that Iran's decision on manufacturing nuclear weapons would be influenced by U.S. policy - and especially by whether the United States was willing to give Iran a firm security guarantee.
