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Paul VI never used the term "artificial contraception." You're making that up.
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As for the rest, Paul VI never exercised his infallibility, neither did John XXIII, John Paul I, Benedict XVI or Francis.
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It would seem they didn't believe in papal infallibility. In fact, it's hard to know WHAT they believe, if anything.
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A friend of mine who recently passed away, Ken Fisher, told me JPII was infallible when he said that women can't be ordained priests.
Which is an objective fact in truth.
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Later, Benedict XVI was asked about that and he replied that JPII did not INTEND to exercise papal infallibility when he said that, and therefore it was not infallible. (Even though it was true!) So perhaps Benedict believes in it; I'm not convinced, though.