cogitation vs introspection

cogitation

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

  • A carefully considered thought, idea, notion. 

introspection

noun
  • A looking inward; specifically, the act or process of self-examination, or inspection of one's own thoughts and feelings; the cognition which the mind has of its own acts and states 

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