rationale

noun

1. An explanation of the basis or fundamental reasons for something.
2. A justification or rationalization for something.

   “He confirmed that Bashir successfully manipulated Diana’s paranoia by showing her brother, Earl Spencer, forged documents that “proved” her closest advisers had betrayed her to the palace, inflaming her desire to speak out for herself. Bashir lied his way to the biggest TV scoop of the 20th century. Dyson’s censure at least gave her two sons some rationale for why Diana did something so destructive to their happiness.”

3. (rare)A liturgical vestment worn by some Christian bishops of various denominations.

   “the local bishop, H.E. Gregor Maria Hanke, is shown wearing that rarest of liturgical garments, the rationale.”