It follows from Principle #3 that:
The Magisterium alone has the authority to say what are the boundaries of its authority, which of its teachings are infallible and which are not infallible and, more generally, what level of authority each of its teachings has.
If this were not true, then it would fall on the individual believer to decide what authority a given teaching has, which would be to make the individual himself the authority. In other words, it would contradict the very purpose of the Magisterium.
This principle is violated constantly by those who say, for example, that Vatican II was not a valid council–or by the gentleman of may acquaintance who maintains that Vatican II was valid but not Vatican I. Given that the Magisterium today accepts both Vatican councils, to hold the positions just mentioned is to say that the Magisterium itself does not know which of its teachings are authoritative.
The principle is also violated by those who do not accept the Church’s teaching on papal infallibility. They imply that the individual has to judge the limits of the Church’s authority, which leaves the individual judging the authority of a given teaching, which violates the purpose of the Magisterium.
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