If a future Pope teaches anything contrary to the Catholic Faith, do not follow him.

The Roman Pontiffs have always...held that all those rites should be preserved which deviate neither from accuracy in matters of faith, nor from what is fitting.

I have always condemned Liberal Catholicism and I will condemn it again forty times over if it be necessary.

If anyone says that it is possible that at some time, given the advancement of knowledge, a sense may be assigned to the dogmas propounded by the Church which is different from that which the Church has understood and understands: let him be anathema.

Socialism, Communism, clandestine societies, Bible societies... pests of this sort must be destroyed by all means.

The Church is built on the rock of Peter, and he who eats the Lamb outside this holy dwelling is reprobate .. .He who eats the Lamb outside this Apostolic See has no part with God!

[Dr. Constain James] refuted so well the aberrations of Darwinism.... [A system] which is repugnant at once to history, to the tradition of all people, to exact science, to observed facts, and even to reason itself, would seem to need no refutation. But the corruption of this age, the machinations of the perverse, the danger of the simple, demand that such fancies, altogether absurd though they are, should - since they borrow the mask of science - be refuted by true science.