In his 1951 book "On the Value of
Theological Notes and the Criteria for Discerning Them" (which was written for
use by auditors of the Roman Congregations) Fr. Sixtus Cartechini, S.J., explains
that the rejection of a dogmatic fact is a “mortal sin against faith”. And the example he uses of a dogmatic fact is
the legitimacy of a determine Pope. See
here: http://www.the-pope.com/theolnotes.html
