formality vs propriety

formality

noun
  • Something said or done as a matter of form. 

  • A specific requirement for obtaining a legal status, conducting a transaction, etc. 

  • A customary ritual without new or unique meaning. 

  • The state of being formal. 

propriety

noun
  • The fact of possessing something; ownership. 

  • Suitability, fitness; the quality of being appropriate. 

  • Correctness in behaviour and morals; good manners, seemliness. 

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