soundness vs stalwartness

soundness

noun
  • The state or quality of being sound. 

  • The result or product of being sound. 

  • The property (of an argument) of not only being valid, but also of having true premises. 

  • The property of a logical theory that whenever a wff is a theorem then it must also be valid. Symbolically, letting T represent a theory within logic L, this can be represented as the property that whenever T⊢𝜙 is true, then T vDash 𝜙 must also be true, for any wff φ of logic L. 

stalwartness

noun
  • The state or condition of being stalwart. 

How often have the words soundness and stalwartness occurred in a corpus of books? (source: Google Ngram Viewer )