consent vs say so

consent

verb
  • To express willingness, to give permission. 

  • To cause to sign a consent form. 

  • To agree in opinion or sentiment; to be of the same mind; to accord; to concur. 

noun
  • Voluntary agreement or permission. 

say so

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