Pius IX, 1846-1878

among Christians be torn out by the roots and that all Christians be "careful to keep the unity of the Spirit in the bond of peace" [Eph. 4:3]. . . . But, that the faithful of Christ and the clergy should pray for Christian unity under the leadership of heretics, and, what is worse, according to an intention, polluted and infected as much as possible with heresy, can in no way be tolerated. The true Church of Jesus Christ was established by divine authority, and is known by a fourfold mark, which we assert in the Creed must be believed; and each one of these marks so clings to the others that it cannot be separated from them; hence it happens that that Church which truly is, and is called Catholic should at the same time shine with the prerogatives of unity, sanctity, and apostolic succession. Therefore, the Catholic Church alone is conspicuous and perfect in the unity of the whole world and of all nations, particularly in that unity whose beginning, root, and unfailing origin are that supreme authority and "higher principality"¹ of blessed PETER, the prince of the Apostles, and of his successors in the Roman Chair. No other Church is Catholic except the one which, founded on the one PETER, grows into one "body compacted and fitly joined together" [Eph. 4:16] in the unity of faith and charity. . . .

1687. Therefore, the faithful should especially shun this London society, because those sympathizing with it favor indifferentism and engender scandal.

Naturalism, Communism, Socialism²

[From the Encyclical, "Quanta cura," Dec. 8, 1864]

1688. Moreover, although We have not failed to proscribe and frequently condemn the most important errors of this sort, nevertheless, the cause of the Catholic Church and the salvation of souls divinely entrusted to Us, and the good of human society itself, demand that We again arouse your pastoral solicitude to overcome other base opinions which spring from these same errors as from fountains. These false and perverted errors are to be the more detested because they have this goal in mind: to impede and remove that salutary force which the Catholic Church, according to the institution and command of her divine founder, must exercise freely "unto the consummation of the world" [Matt. 28:20], no less toward individual men, than toward nations, peoples, and their highest leaders; and to remove that mutual alliance of councils between the sacerdotal ministry and the government, and that "happy concord