noun (n)

• (law) an explanation of the fundamental reasons (especially an explanation of the working of some device in terms of laws of nature)(noun.cognition)

  Example:
  The rationale for capital punishment.
  

  Synonym:
  principle
  

  source: wordnet30
• An explanation or exposition of the principles of some opinion, action, hypothesis, phenomenon, or the like; also, the principles themselves.(noun)

  source: webster1913