Both the Syllabus of Errors and the Oath Against Modernism condemn the ideas that 1) a man may be saved in a false religion and 2) that a good-willed man, who follows the natural law, can have supernatural Faith, which saves.
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Syllabus of Errors – Bl Pope Pius IX - 1864
16. Man may, in the observance of any religion whatever, find the way of eternal salvation, and arrive at eternal salvation. — Encyclical “Qui pluribus,” Nov. 9, 1846.
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Pope St Pius X's "Oath Against Modernism" of 1910
Fifthly, I hold with certainty and sincerely confess that faith is not a blind sentiment of religion welling up from the depths of the subconscious under the impulse of the heart and the motion of a will trained to morality; but faith is a genuine assent of the intellect to truth received by hearing from an external source.
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By this assent, because of the authority of the supremely truthful God, we believe to be true that which has been revealed and attested to by a personal God, our creator and lord.