Try to talk out of - with justification (6)
I believe the answer is:
reason
'justification' is the definition.
(I know that reason is a type of justification)
I don't understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for reason that I've seen before include "Motive; argue" , "Cause; mind's power" , "Motive or right thinking" , "Justification or motive" , "Cause - logic" .)