Independent supporting a religious leader from general principles (1,6)
I believe the answer is:
a priori
'from general principles' is the definition.
(term in logic)
'independent supporting a religious leader' is the wordplay.
'independent' becomes 'i'.
'supporting' says to put letters next to each other (in a down clue, some letters go below others).
'religious leader' becomes 'prior' (I've seen this before).
'a'+'prior'='aprior'
'i' put after 'aprior' is 'A PRIORI'.
(Other definitions for a priori that I've seen before include "form of reasoning" , "Of reasoning, from cause to effect - in Latin" , "'Derived by logic, without observed facts (1,6)'" , "reasoned logically" , "Sort of reasoning" .)