rationale
1. [ noun ] (law) an explanation of the fundamental reasons (especially an explanation of the working of some device in terms of laws of nature)
Synonyms: principle
Examples:

"the rationale for capital punishment" "the principles of internal-combustion engines"

Related terms: explanation dialectics law
Similar spelling:   rational
  rationalize
  rationalise
  rationalness
  rationally
  rationality
  rationalist
  rationalism