On December 8, 1864, Pope Pius IX issued an encyclical letter titled Quanta Cura ("With Great Care"). He directed the Church's hierarchy to oppose what he called a "great perversity of depraved opinions." Calling on his "apostolic authority," the pope condemned certain "evil opinions and doctrines" and commanded Catholics to eschew them as well.
Accompanying the publication of Quanta Cura was a listing of 80 condemned propositions in a document now known as Pope Pius IX's Syllabus of Errors. Public reaction to the Syllabus, even among Catholics, was largely negative, sometimes hostile.
The problem was: The list included not only opinions which were in essence opposed to Catholic dogma, but also ideas which were not necessarily contrary to dogma.
For example, the Syllabus condemned the proposition that belief in Christ is irrational and that divine revelation is harmful to the perfection of the human race. There was little opposition to condemning that idea.
On the other hand, the Syllabus condemned the proposal that "every man is free to embrace and profess that religion which, guided by the light of reason, he shall consider true." There was much opposition to this condemnation of freedom of conscience.
Whoever put the list together committed himself a great error. The compiler took statements out of context, statements of errors previously condemned in Church and papal documents. For example, taken out of context, the idea that the pope should not come to terms with modern civilization is nonsensical, and yet that is what Error #80 seemed to say. The problem here is that the pope was using the term "civilization" in a very restricted, almost sarcastic way, to refer to new movements which undermined the Church.
At the same time, however, not all "errors" were misunderstandings. Some of the ideas condemned in the Syllabus were later recanted, or re-interpreted.
For example, the Syllabus denied that there are myths in the Bible (#7). As noted above, the pope considered freedom of religion to be untenable (#15). The list condemned the suggestion that the papacy had contributed to the division of the Church into Eastern and Western (#38). And the Syllabus insisted that it was an error to hold that "The Church ought to be separated from the State, and the State from the Church" (#55). Today we do not think of these ideas as errors.
Today the Church lends support to the idea of the separation of Church and State (see Vatican II's Declaration on Religious Liberty), even though the Syllabus condemned it.
Today Catholics are urged to engage in ecumenical dialogue (see Vatican II's Decree on Ecumenism) even though in 1928 Pope Pius XI condemned the ecumenical movement (see Pius XI's Mortalium animos).
Today Catholics do not believe that Jews are rejected by God and accursed as Christ-killers (see Vatican II's Nostra aetate) even though in the 18th century Pope Pius VI forced Jews in the Papal States to live in ghettos and required them to wear badges identifying them as Jews.
The point is: The Church or, more correctly, its members, must expect to grow in understanding and to refine its practices. Of course there are dogmas that will never change; we will never in the future deny Jesus' divinity or Christ's resurrection. But not every papal opinion is dogma. Further there are times when our sitz-im-leben changes, and we must change how we think about it.
The New Testament gives Jesus' assurance that he will send the Spirit of truth to "guide you to all truth...he will declare to you the things to come" (John 16:13). Scholar Raymond Brown's exegesis of that passage is most helpful: "The declaration of the things to come consists in interpreting in relation to each coming generation the contemporary significance of what Jesus has said and done."
We have then a Spirit that helps us to grow in our understanding and to make course corrections when we go astray. With that assurance, we need not fear change or development. The Spirit of God moves us toward the truth.