affirmation vs assertion

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. 

assertion

noun
  • Something which is asserted; a declaration; a statement asserted. 

  • A statement in a program asserting a condition expected to be true at a particular point, used in debugging. 

  • A statement or declaration which lacks support or evidence. 

  • The act of asserting; positive declaration or averment. 

  • Maintenance; vindication 

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