affirm vs avow

affirm

verb
  • To state under a solemn promise to tell the truth which is considered legally equivalent to an oath, especially of those who have religious or other moral objections to swearing oaths; also solemnly affirm. 

  • To make firm; to confirm, or ratify; especially (law) to assert or confirm, as a judgment, decree, or order, brought before an appellate court for review. 

  • To agree, verify or concur; to answer positively. 

  • To assert positively; to tell with confidence; to aver; to maintain as true. 

  • To support or encourage. 

avow

verb
  • To acknowledge and justify, as an act done. See avowry. 

  • To declare openly and boldly, as something believed to be right; to own, acknowledge or confess frankly. 

  • To bind or devote by a vow. 

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