It is clear in Catholic doctrine that Church teaching is authoritative, as it comes from Christ, and is reliable to lead to truth, as it is guided by the Holy Spirit, and that therefore Catholics are required to assent to it. The Church can teach in both a definitive manner and a non-definitive manner. When the Church teaches definitively, Catholics are obliged to accept the teaching definitively and absolutely. When the Church teaches with less than full definitiveness, Catholics are obliged to accept the teaching to the degree and in the form required by the intention of the teacher. The Church has spelled out this schema in many places, such as in the CDF (Congregation for the Doctrine of the Faith) document Donum Veritatis (1990):
When the Magisterium of the Church makes an infallible pronouncement and solemnly declares that a teaching is found in Revelation, the assent called for is that of theological faith. This kind of adherence is to be given even to the teaching of the ordinary and universal Magisterium when it proposes for belief a teaching of faith as divinely revealed.When the Magisterium proposes "in a definitive way" truths concerning faith and morals, which, even if not divinely revealed, are nevertheless strictly and intimately connected with Revelation, these must be firmly accepted and held.When the Magisterium, not intending to act "definitively", teaches a doctrine to aid a better understanding of Revelation and make explicit its contents, or to recall how some teaching is in conformity with the truths of faith, or finally to guard against ideas that are incompatible with these truths, the response called for is that of the religious submission of will and intellect. This kind of response cannot be simply exterior or disciplinary but must be understood within the logic of faith and under the impulse of obedience to the faith. (#23, footnotes removed)
The CDF, in its Doctrinal Commentary on the Concluding Formula of the Professio fidei (1998), articulated that "teachings set forth by the authentic ordinary Magisterium in a non-definitive way . . . require degrees of adherence differentiated according to the mind and the will manifested; this is shown especially by the nature of the documents, by the frequent repetition of the same doctrine, or by the tenor of the verbal expression" (#11). This language was echoing the Vatican II document Lumen Gentium, #25, which said this:
Bishops, teaching in communion with the Roman Pontiff, are to be respected by all as witnesses to divine and Catholic truth. In matters of faith and morals, the bishops speak in the name of Christ and the faithful are to accept their teaching and adhere to it with a religious assent. This religious submission of mind and will must be shown in a special way to the authentic magisterium of the Roman Pontiff, even when he is not speaking ex cathedra; that is, it must be shown in such a way that his supreme magisterium is acknowledged with reverence, the judgments made by him are sincerely adhered to, according to his manifest mind and will. His mind and will in the matter may be known either from the character of the documents, from his frequent repetition of the same doctrine, or from his manner of speaking.
In modern times, those who have wished to dissent from some of the authoritative teachings of the Church in defiance of the Church's authority have sometimes attempted to justify their defiance by redefining "submission of mind and will" into something like "respectful consideration." In their view, one must consider seriously the Church's non-definitive teaching, but one must not trust it implicitly. One must use one's own private judgment to evaluate that teaching, and then one is justified in rejecting that teaching if it fails that private investigation. Thus, whereas, with definitive teaching, the rule of belief is the Church's teaching, the rule of belief with regard to non-definitive teaching is not the authority of the Church but the agreement of the Church's teaching with one's private, independent judgment and confirmation.
A classic example of this kind of dissent is seen in the attitude of the Society of St. Pius X, which was founded by Archbishop Marcel Lefebvre in 1970 to continue what Lefrebre regarded as "authentic" Catholic faith and practice in opposition to what he considered to be the errors and deviations of the modern Church after Vatican II. Lefebvre and his followers wanted to reject portions of Vatican II on the grounds that the Council did not intend to affirm anything in the form of a solemn, definitive declaration, but only under the authority of the "ordinary" magisterium, which they held to be subject to their private judgment. But that loophole had already been cut off by the Council itself, as well as by Pope St. Paul VI, such as in his General Hearing of January 12, 1966:
There are those who ask what authority, what theological qualification the Council intended to give to its teachings, knowing that it avoided issuing solemn dogmatic definitions engaging the infallibility of the ecclesiastical Magisterium. The answer is known by whoever remembers the conciliar declaration of March 6, 1964, repeated on November 16, 1964: given the Council’s pastoral character, it avoided pronouncing, in an extraordinary manner, dogmas endowed with the note of infallibility. But it has invested its teachings with the authority of the supreme ordinary magisterium, which ordinary magisterium is so obviously authentic that it must be accepted with docility and sincerity by all the faithful, according to the mind of the Council as expressed in the nature and aims of the individual documents. (Pope St. Paul VI, General Hearing, Wednesday, January 12, 1966, following the translation found here by Dr. Jeff Mirus)
Pope St. Paul VI, in a letter to Archbishop Lefebvre in 1976, reminded him of this fact:
Again, you cannot appeal to the distinction between what is dogmatic and what is pastoral to accept certain texts of this Council and to refuse others. Indeed, not everything in the Council requires an assent of the same nature: only what is affirmed by definitive acts as an object of faith or as a truth related to faith requires an assent of faith. But the rest also forms part of the solemn magisterium of the Church to which each member of the faithful owes a confident acceptance and a sincere application. ("Pope Paul VI's Letter to Archbishop Marcel Lefebvre", found on the Word on Fire website)
Now, it is true that non-definitive magisterial teachings can contain in them elements of varying degrees of authority. The less formal, more "casual" (for lack of a better word) nature of the format of these teachings allows for such a mix. Sometimes there are elements of non-definitive teachings that are provisional in nature, tied to the circumstances of the times and therefore subject to change as circumstances change, and sometimes there are incidental observations that the mind and the will of the magisterial teacher does not intend to put forward as authoritative teachings binding the minds of the faithful. The Church tells us to use common sense, combined with good reading and listening skills--as well as asking for clarification if necessary--when we listen to non-definitive teachings and decide what response they call forth from us. Sometimes magisterial decisions, particularly practical or prudential decisions, involve elements that can even invite respectful criticism from the faithful. When the "mind and the will manifested" of the magisterial teacher allows such respectful criticism, it is legitimate and not a form of dissent from or defiance of the authority of the Church. The CDF made this point explicitly in Donum Veritatis:
The willingness to submit loyally to the teaching of the Magisterium on matters per se not irreformable must be the rule. It can happen, however, that a theologian may, according to the case, raise questions regarding the timeliness, the form, or even the contents of magisterial interventions. Here the theologian will need, first of all, to assess accurately the authoritativeness of the interventions which becomes clear from the nature of the documents, the insistence with which a teaching is repeated, and the very way in which it is expressed. (#24, footnote removed)One must therefore take into account the proper character of every exercise of the Magisterium, considering the extent to which its authority is engaged. It is also to be borne in mind that all acts of the Magisterium derive from the same source, that is, from Christ who desires that His People walk in the entire truth. (#17)
But there is a fine line between legitimate criticism, within the bounds the Church has allowed, and dissent from Church teaching that involves defiance of the Church's authority. Sometimes that line can be hard to see, and certain forms of expression can have the effect of obscuring that line. For example, in 1968, the Catholic bishops of the United States issued a pastoral letter entitled "Human Life in Our Day". Part of the impetus for this document was to defend Pope St. Paul VI's encyclical Humanae Vitae, which was very unpopular in "progressive" circles and was drawing a great deal of dissent. But in the course of this pastoral letter, the US bishops tried to lay out some boundaries for legitimate dissent and criticism. They said that professional theologians could, in limited circumstances, dissent from certain non-infallible magisterial teachings, provided they do so with great care and caution, respect for the consciences of others, in an appropriate manner, etc.
When there is question of theological dissent from non-infallible doctrine, we must recall that there is always a presumption in favor of the magisterium. Even non-infallible authentic doctrine, though it may admit of development or call for clarification or revision, remains binding and carries with it a moral certitude, especially when it is addressed to the universal Church, without ambiguity in response to urgent questions bound up with faith and crucial to morals. The expression of theological dissent from the magisterium is in order only if the reasons are serious and wellfounded, if the manner of the dissent does not question or impugn the teaching authority of the Church and is such as not to give scandal. (Found here on the EWTN website, taken from L'Osservatore Romano, Weekly Edition in English, 12 December 1968, page 6 and 19 December 1968, page 5)
It has been observed that this last sentence is very ambiguous and could lend itself to being made use of by dissenters who wish to dissent from teaching the Church intends to bind them to, dissenters like Archbishop Lefebvre and his SSPX movement. (Although, in the case of Humanae Vitae, the dissent was rather from the more liberal, "progressive" side of the Church.) Catholic apologist Jimmy Akin discusses this in his book Teaching With Authority (El Cajon, CA: Catholic Answers Press, 2018). He provides an interesting commentary from Cardinal Avery Dulles on the apparent subjectivity of the US bishops' criteria for legitimate dissent:
Cardinal Avery Dulles remarked that these conditions "proved difficult to apply. Who was to say whether the reasons were well-founded? How could one establish that the authority of the Magisterium was not being impugned when its teaching was being denied? How could scandal be avoided when theologians were openly saying that the pope's teaching was wrong?" [The Dulles quote is from The Craft of Theology: From Symbol to System, 2nd ed. (New York: Crossroad, 1996), 113.]
"Human Life in Our Day" was issued in 1968. Since that time, the Church has issued several documents clarifying further the assent required of non-definitive teachings, including the CDF document we've quoted from a few times now, Donum Veritatis, and also the CDF commentary on the Professio Fidei, also quoted from earlier. Donum Veritatis in particular focuses a good deal of attention on the illicitness of "dissent", while at the same time distinguishing it from legitimate dialogue and even criticisms that can sometimes be made with regard to magisterial pronouncements. The US bishops, in 1992, issued another document entitled The Teaching Ministry of the Diocesan Bishops: A Pastoral Reflection (Washington, D.C.: United States Catholic Conference, 1992). In this document, the bishops are much more careful to make clear that dissent to Church teaching is not acceptable and that the Catholic faithful are required to assent to the non-definitive teaching of the Church with "submission of will and intellect." They distinguish various forms of refusal of assent to non-definitive teachings--non-acceptance, private dissent, and public dissent--and they make it clear that all three are unacceptable.
Perhaps, a more common experience of nonacceptance in the Church today is the withholding of assent to what is identified as nondefinitive teaching. . . . While these manifestations of nonacceptance may fall short of outright rejection, nevertheless they remain nonacceptance, the withholding of the religiosum voluntatis et intellectus obsequium [religious submission of mind and will] due to the ordinary magisterium of the Church. . . .Quite distinct from the withholding of assent is the private, individual judgment that conclusively rejects the ordinary, nondefinitive teaching of the Church. Such a judgment constitutes private dissent and is not consistent with that religiosum voluntatis et intellectus obsequium due to church teaching. Even though dissent of this kind remains private, nevertheless it is unacceptable. . . .Sometimes the nonacceptance of nondefinitive teaching passes beyond the nature of a "difficulty" and becomes a judgment that an authoritative teaching is false. This, of course, is quite different from a critical judgment about the adequacy of expression or the conceptual limitations of a particular teaching. . . .Bishops cannot be indifferent to the public denial or the contradiction of church teaching, especially by those whose position confers public influence. Public dissent, especially in the form of advocacy for alternative positions, seriously impairs the Church as a communion of faith and witness. (Teaching Ministry, pp. 17-19, footnotes removed)
The document recognizes that the "ordinary, nondefinitive teaching of individual popes and bishops may contain assertions that fall short of the full truth of the gospel and may be in need of development and amplification. Interventions in the prudential order may even be in need of correction" (p. 15). "At times . . . professional theologians or other competent persons may conclude that the search has not been completed or that what has been asserted is still imperfect, and their acceptance will be qualified accordingly" (p. 15). Scholars may discuss difficulties in professional journals, etc. However, "[t]these considerations presume that theologians and scholars are willing to take the necessary steps to overcome their difficulties and abide by an authoritative intervention on the part of the magisterium should it consider one necessary" (p. 18).
Finally, the disposition toward the teaching authority of the bishop on the part of those who are dissenting must be taken into consideration. If an individual or group dissents, but retains the disposition to abide by a final judgment of the magisterium on an issue, the possibility of obsequium religiosum remains. On the other hand, if dissent is expressed in absolute terms and there are no signs of docility toward the Church, that possibility may well be foreclosed. In that case, the bishop may initiate the process leading to the possible imposition of a canonical penalty (cf. c. 1371.1). (p. 19).
(I should mention that this document, as well as Donum Veritatis and many of the other documents I've mentioned, are rich with pastoral suggestions regarding how to deal with people who struggle with certain Church teachings, sometimes in good conscience. I cannot do justice to this aspect of the documents, or other important nuances, as well as the significant amount of good practical wisdom these documents contain, in such a short article as this.)
In conclusion, as we said earlier, we can indeed, at times, criticize and even disagree with some of the things the bishops and the Pope say. But the real question is, Who determines the degree and form of assent required in any particular case? The erroneous dissenters make themselves and their own judgment the determining factor in deciding what they are required to assent to and to what degree they are required to assent. But the Church teaches that it is the bishops and the Pope who make that determination. This is the fundamental point and the fundamental difference between legitimate diversity and criticism and illegitimate dissent and defiance. We don't get to subject the teachings of the bishops and the Pope to our own judgment and decide, even against their intentions and requirements, what we will agree with and what we will disagree with. We must assent to their teaching according to their manifest mind and will. We must accept even non-definitive magisterial teaching as inherently reliable, so that we will not subject it to our judgment and disagree with it if the "validity of the given teaching is not evident or upon the opinion that the opposite position would be the more probable" (Donum Veritatis, #28) So while there can sometimes legitimately be disagreement with some things the Pope or bishops say, there can never be dissent from magisterial teaching, in the sense of refusal to accept magisterial teaching to the extent that it is intended as authoritative and binding. Whenever and to the extent that the bishops and/or the Pope make use of their magisterial authority with the intention to give to the Church an authentic, official teaching, leading the people of God into truth or showing them how to stay faithful to the truth, that teaching must be assented to.