Soundness
Part of speech: noun
Definition: The state or quality of being sound. The result or product of being sound.
Firmness
Part of speech: noun
Definition: The state of being firm; strength; permanence; stability; hardness; resolution.
Example sentence: Since coming to Harwell I have met English people of all kinds, and I have come to see in many of them a deep rooted firmness which enables them to lead a decent way of life.