Is it better to say argumentum a/ab contrario or e/ex contrario?
It seems that both are acceptable but in most Romance languages it is a contrario.
The movement out/from is not clear/explicit/graphic and it is a concept/mental abstraction that "moves", not a physical object.
EDIT secondary questions following up to clarify as suggested Why ex and not ab? Why do most Romance Languages have a contrario instead? How did ex contrario evolve to a contrario?