ignorance vs letters

ignorance

noun
  • The condition of being uninformed or uneducated; lack of knowledge or information. 

  • Sins committed through ignorance. 

letters

noun
  • Literature (school subject). 

  • The liberal arts, humanities, learning (broad accumulated cultural knowledge). 

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