affirm vs approve

affirm

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

  • 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 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 support or encourage. 

approve

verb
  • To consider worthy (to); to be pleased (with); to accept. 

  • To officially sanction; to ratify; to confirm; to set as satisfactory. 

  • To make profit of; to convert to one's own profit — said especially of waste or common land appropriated by the lord of the manor. 

  • To regard as good; to commend; to be pleased with; to think well of. 

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