Reason, justification (9)
I believe the answer is:
rationale
I believe this is a double definition.
'reason' is the first definition.
(I've seen this before)
'justification' is the second definition.
(I know that justification can be written as rationale)
(Other definitions for rationale that I've seen before include "Motivation" , "grounds?" , "Why regulate" , "Basis of logic" , "justification" .)