XIX. The following things must belong to fundamental articles:
(1) that they be catholic, for the things necessary for the salvation of everyone are required for a universal faith (according to the Athanasian Creed “whoever wishes to be saved must above all things hold the catholic faith; for unless it is held entire and inviolate he will perish forever” [cf. Schaff, 2:66]);
(2) that the belief of the catholic truths necessarily draws salvation after it; and the ignorance of them, the entire doubt of danger, the impious and heretical denial, is damnable;
(3) that believers cherish a true consent to them, nor do some think differently from others because if anyone thinks or speaks otherwise he is subjected to the curse (Gal. 1:8). Hence where a difference in fundamentals exists, there cannot be union.
(4) That all theological doctrines be reduced to them as to a rule which the apostle calls the analogy of faith (analogian pisteōs);
(5) that they be primary and principal truths upon which all others are built as upon a foundation—and being removed, faith itself is overthrown; not secondary and less principal, by the removal of which faith is only shaken.
Francis Turretin, Institutes of Elenctic Theology, ed. James T. Dennison Jr., trans. George Musgrave Giger, vol. 1 (Phillipsburg, NJ: P&R Publishing, 1992–97), 1.14.19.