insist vs persist

insist

verb
  • To demand continually that something happen or be done; to reiterate a demand despite requests to abandon it. 

  • To hold up a claim emphatically. 

persist

verb
  • To go on stubbornly or resolutely. 

  • To repeat an utterance. 

  • To cause to persist; make permanent. 

  • To continue to exist. 

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