A certain sect, which you surely know, has unjustly arrogated to itself the name of philosophy, and has aroused from the ashes the disorderly ranks of practically every error. Under the gentle appearance of piety and liberality this sect professes what they call tolerance or indifferentism. It preaches that not only in civil affairs, which is not Our concern here, but also in religion, God has given every individual a wide freedom to embrace and adopt without danger to his salvation whatever sect or opinion appeals to him on the basis of his private judgment. The apostle Paul warns us against the impiety of these madmen. “I beseech you, brethren, to behold those who create dissensions and scandals beyond the teaching which you have learned. Keep away from such men. They do not serve Christ Our Lord but their own belly, and by sweet speeches and blessings they seduce the hearts of the innocent.”

Of course this error is not new, but in Our days it rages with a new rashness against the constancy and integrity of the Catholic faith. Eusebius cites Rhodo as his source for saying that the heretic Apelles in the second century had already produced the mad theory that faith should not be investigated, but that each man should persevere in the faith he was raised in. Even those who put faith in a crucified man were to be saved, according to Apelles, provided that they engaged in good works. Rhetorius too, as We learn from St. Augustine, used to claim that all the heretics walked on the right road and spoke truth. But Augustine adds that this is such nonsense that he cannot believe it. The current indifferentism has developed to the point of arguing that everyone is on the right road. This includes not only all those sects which though outside the Catholic Church verbally accept revelation as a foundation, but those groups too which spurn the idea of divine revelation and profess a pure deism or even a pure naturalism. The indifferentism of Rhetorius seemed absurd to St. Augustine, and rightly so, but it did acknowledge certain limits. But a tolerance which extends to Deism and Naturalism, which even the ancient heretics rejected, can never be approved by anyone who uses his reason. Nevertheless — alas for the times; alas for this lying philosophy!-such a tolerance is approved, defended, and praised by these pseudophilosophers. – from Ubi Primum (1826)