Reason police dog failed to get dope (5)
I believe the answer is:
logic
'reason' is the definition.
(logic is using reason)
I can't explain the remainder of the clue.
Can you help me to learn more?
(Other definitions for logic that I've seen before include "Rigorous reasoning" , "Rationale ?" , "4-ing" , "Branch of philosophy that analyses inference" , "this makes sense" .)