Five Ways Vatican 2 Condemned Modernism

Vatican II rejected at least five modernist ideas: relativism (Gaudium et Spes 19), religious indifferentism (Lumen Gentium 14), abortion (Gaudium et Spes 27), secularism (Dignitatis Humanae 1), and the idea that the Scriptures can sometimes be false (Dei Verbum 11).

Relativism

About relativism, the Second Vatican Council says:
The word atheism is applied to phenomena which are quite distinct from one another. For while God is expressly denied by some, others believe that man can assert absolutely nothing about Him. Still others use such a method to scrutinize the question of God as to make it seem devoid of meaning. Many...altogether disallow that there is any absolute truth. … Undeniably, those who willfully shut out God from their hearts and try to dodge religious questions are not following the dictates of their consciences, and hence are not free of blame… (Gaudium et Spes 19)
In this passage, the denial of any absolute truth is discussed under the section on atheism, and the Council says that “[those who] try to dodge religious questions” by “disallow[ing] that there is any absolute truth” are “not free of blame.” This is a Conciliar rejection of a modernist idea by the Second Vatican Council. It is one piece of evidence that the Council was not modernist, as some claim it was.

Religious Indifferentism


About religious indifferentism, the Second Vatican Council says:
Basing itself upon Sacred Scripture and Tradition, [this Council] teaches that the Church, now sojourning on earth as an exile, is necessary for salvation. Christ, present to us in His Body, which is the Church, is the one Mediator and the unique way of salvation. In explicit terms He Himself affirmed the necessity of faith and baptism and thereby affirmed also the necessity of the Church, for through baptism as through a door men enter the Church. Whosoever, therefore, knowing that the Catholic Church was made necessary by Christ, would refuse to enter or to remain in it, could not be saved. (Lumen Gentium 14)
In this passage, religious indifferentism is opposed in several ways. For one, the Council says that the Catholic Church “is necessary for salvation.” Indifferentism says that no particular religion is necessary for salvation. Thus, indifferentism is opposed by the proclamation of its opposite.

Also, the statement in which the phrase “could not be saved” appears has the form of a Conciliar decree. Ecumenical councils frequently name an opinion and say that whoever would adopt that opinion will be anathema. This council goes further and says that whoever would adopt the position it condemns could not be saved. This is another point of evidence that the Council was not modernist.

Abortion

About abortion, the Second Vatican Council says:
[W]hatever is opposed to life itself, such as any type of murder, genocide, abortion, euthanasia or wilful self-destruction...all these things and others of their like are infamies indeed. They poison human society... Moreover, they are supreme dishonor to the Creator. (Gaudium et Spes 27)
In this passage, abortion is discussed as one item in a list of actions condemned as sinful. The declaration calls it “[an] infam[y] indeed” which “poison[s] human society” and shows “supreme dishonor to the Creator.” These are some of the strongest words in the Council about particular actions, and abortion is rejected among them. By condemning as sinful an action that modernism regards as morally neutral, the Council gives us another piece of evidence that it was not modernist.

Secularism

About secularism, the Second Vatican Council says:
Religious freedom...has to do with immunity from coercion in civil society. Therefore it leaves untouched traditional Catholic doctrine on the moral duty of men and societies toward the true religion and toward the one Church of Christ. (Dignitatis Humanae 1)
In this passage, the Council makes it clear that it is not promoting secularism by declaring that it “leaves untouched the traditional Catholic doctrine” on the matter. Specifically, the Council says that it recognizes that societies have “[a] moral duty...toward the true religion and toward the one Church of Christ.” Secularism says that society does not have any religious duty at all. Thus, secularism is opposed by the proclamation of its opposite.

But the Council goes further than saying that societies have a moral duty to God. It declares that they have a moral duty toward “the true religion and toward the one Church of Christ.” This can be seen as a call for an established Church. This is corroborated by a later section of the declaration in which the Council's words can be used to defend the constitutional establishment of religion against the claim that it violates the right to religious liberty:
If, in view of peculiar circumstances obtaining among peoples, special civil recognition is given to one religious community in the constitutional order of society, it is at the same time imperative that the right of all citizens and religious communities to religious freedom should be recognized and made effective in practice. (Dignitatis Humanae 6)
Therefore, instead of promoting secularism, the Council says that societies have a moral duty toward God and the Catholic Church, and helps us defend the constitutional recognition of religion against the idea that it violates the right to religious liberty. This is another piece of evidence against the claim that the Second Vatican Council was modernist.

The Inerrancy of the Scriptures

About the inerrancy of the Scriptures, the Second Vatican Council says:
To compose the sacred books, God chose certain men who...consigned to writing whatever he wanted written, and no more. … Since therefore all that the inspired authors or sacred writers affirm should be regarded as affirmed by the Holy Spirit, we must acknowledge that the books of Scripture firmly, faithfully, and without error teach that truth which God, for the sake of our salvation, wished to see confided to the Sacred Scriptures. (Dei Verbum 11)
In this passage, the inerrancy of the Scriptures is discussed in the context of its inspiration. The Council makes it clear that the Church accepts the Scriptures as “firm[,] faithful[,] and without error” and that they contain “whatever [God] wanted written, and no more.” Both of these are incompatible with the modernist idea that Scripture contains errors. Thus, that idea is opposed by the proclamation of its opposite. This is yet another piece of evidence that the Council was not modernist.

Religious Liberty: Modernist or Traditional?

The Council defends a limited right to religious liberty in the document Dignitatis Humanae. Modernists also believe in religious liberty, which makes some people think the Council capitulated to modernism on this matter. However, although the Council did teach that religious conformity should not be coerced, that is not a new idea, but is an ancient part of Catholic tradition, with roots in the Church Fathers and the scholastic theologians.

See here for examples.

For all these reasons, the Second Vatican Council was not modernist, but rather condemned many modernist ideas. I hope readers find this information useful when confronting challenges to the legitimacy of the Second Vatican Council.