Motive, reason (5)
I believe the answer is:
cause
This clue is a double definition.
'motive' is the first definition.
(I've seen this before)
'reason' is the second definition.
(I know that reason can be written as cause)
(Other definitions for cause that I've seen before include "A movement or charity- usually good" , "Bring about" , "It brings about an effect" , "why some people fight" , "Reason; belief" .)