Reasoned correctly, US soldier must be in pub (7)
I believe the answer is:
logical
'reasoned correctly' is the definition.
(logical means reasoned or rational)
'us soldier must be in pub' is the wordplay.
'us soldier' becomes 'GI' (informal term for a US soldier).
'must be in' means one lot of letters goes inside another.
'pub' becomes 'local' (one's local pub).
'gi' inserted into 'local' is 'LOGICAL'.
(Other definitions for logical that I've seen before include "Well-reasoned" , "Sound" , "Using reason" , "Deductive" , "Deducible" .)