- Extra ecclesiam nulla salus est (major premise, a well-established principle by that point).
- Membership in the true Church requires [WILLFUL] subjection to the Roman Pontiff (minor premise)
- Therefore,** [WILLFUL**] subjection to the Roman Pontiff is necessary to salvation (conclusion).**
I have inserted the bolded word, of course, because it is something which I believe that you assume here, but which you have not made clear.
With the insertion of this word, we can see quite clearly that Boniface VIII could have not have possibly intended to use this syllogism in the way that you are.
Why not?
It would have Boniface VIII believing that infants can be outside the Church, since they cannot will to have subjection to the Pope. This is ridiculous: he certainly would have held that infants can be baptized, and that they therefore are members of the Church.
We can see, therefore, that Boniface intended IMPLICIT submission to the Roman Pontiff as being necessary for salvation, and it is the nature of such an implicit submission which has been subject to doctrinal development.
Development. Not contradiction.
Please see Fr. Harrison’s excellent treatment of this here:
rtforum.org/lt/lt150.html