We need to address the root of sedevacantism, which is the overrating of authority with respect of the truth, says Bishop Williamson, a notorious Thomist: “Thus, in Faith, if we consider the formal reason of its object, is nothing else than the First Truth. The Faith we are talking about does not assent anything unless it is revealed by God; hence it relies on the First Truth as a means.” (I, II, I, 1,c). Further, St. Thomas states again that the rule of Faith is the “Veritas Prima”: “The rule of Faith for a heretic is his own will, not the First Truth.” (II,II,5,3,c.) Indeed “Faith, as far as the assent is concerned, which is the principal act of faith, comes from God, moving [the soul] interiorly by Grace.” (id. Q.6,1,c.).
When then is the role of the popes with respect to the faith? They cannot change the substance, only increase the explanation, transforming implicit articles of Faith to explicitness (id. 1,7,c.). The authority of the Pontiff clears emerging difficulties (id. 1,10,c.&ad1) and “whatever Synod observed that the following Synod defines something above what the other Synods had exposed; because of the necessity of some rising heresy.” (id. Ad1).
Hence, says Bishop Williamson, “the deposit is closed; neither the ordinary universal Magisterium, nor the extraordinary Magisterium add anything.” (EC 343) “Our Lady’s Immaculate Conception is first a reality, then a truth, then a definition because of our human intellectual frailty, needing certainty on what already is. IT is like a snowcap that descends on Charity grows cold, a sign of weakness.” (EC 343) “At the death of St. John, the deposit is a body of doctrine, not only infallible, but also complete. Our Lord authorized Tradition and in turn Tradition authorizes the Magisterium. Since Vatican II is out of Tradition from the onset, it is a no starter.” (EC 358) “The hallmark of the ordinary and universal Magisterium is not solemnity, but its correspondence with Tradition” (EC 357) “Universal” means this connection of the Magisterium with the past, [not its solemnity].” (EC 342) (François Chazal, Contra Cekadam [Salve Regina Publications, n.d.], 69)