cogitation vs illation

cogitation

noun
  • The process of cogitating; contemplation, deliberation, reflection, meditation. 

  • A carefully considered thought, idea, notion. 

illation

noun
  • The act of inferring or concluding, especially from a set of premises; a conclusion, a deduction. 

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