affirmation vs approval

affirmation

noun
  • That which is affirmed; a declaration that something is true. 

  • A form of self-forced meditation or repetition; autosuggestion. 

  • The solemn declaration made by Quakers and others incapable of taking an oath. 

approval

noun
  • An expression granting permission; an indication of agreement with a proposal; an acknowledgement that a person, thing, or event meets requirements. 

  • Something mailed by a seller to a collector to match their stated interests; the collector can approve of or return the item. 

  • An expression of favorable acceptance and encouragement; a compliment that also condones. 

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