probity vs rectitude

probity

noun
  • Integrity, especially of the quality of having strong moral principles; decency and honesty. 

rectitude

noun
  • Conformity to the rules prescribed for moral conduct; (moral) uprightness, virtue. 

  • Straightness; the state or quality of having a constant direction and not being crooked or bent. 

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