There is an alarming tendency among theologians and the laity in general to treat nearly all matters of faith or morals as open questions.
Unless there is an infallible magisterial teaching on a particular point, explicitly stated in clear language, they treat the matter as if it were an open question. Worse still, they narrow the extent of infallible teachings: admitting very few papal teachings as infallible, narrowing the interpretation of Conciliar infallible teachings, and claiming that various teachings under the Universal Magisterium have not yet been universally and definitively taught. Neither do they admit that if the Magisterial infallibly teaches A and B, and if C necessarily follows from A and B, that C is a required belief.
To the contrary, the faithful are obliged by the moral law to adhere to all of the infallible teachings of the Magisterium (formal dogma).
Can. 750 §1. “A person must believe with divine and Catholic faith all those things contained in the word of God, written or handed on, that is, in the one deposit of faith entrusted to the Church, and at the same time proposed as divinely revealed either by the solemn magisterium of the Church or by its ordinary and universal magisterium which is manifested by the common adherence of the Christian faithful under the leadership of the sacred magisterium; therefore all are bound to avoid any doctrines whatsoever contrary to them.”
Teachings under the Universal Magisterium require the full assent of faith no less so than teachings under Papal Infallibility or Conciliar Infallibility. The obstinate rejection or obstinate doubt of any such teaching is the sin of heresy. And if any set of infallible teachings necessarily implies that any assertion on any matter of faith or morals is false, the faithful are obliged to reject that false assertion. For whenever any assertion or theological proposition is incompatible with any infallible teaching, the adherence to that assertion is also the sin of heresy. The sin of heresy can be committed directly, by the denial or refusal to believe an infallible teachings, or it can be committed indirectly, by the adherence to an assertion that is fundamentally incompatible with any infallible teaching or set of infallible teachings.
In addition, everything taught by Sacred Tradition and Sacred Scripture is per se an infallible teaching of Divine Revelation (material dogma). Therefore, the moral law requires the faithful to adhere to all such teachings, which are clear and definitive, even if not yet taught infallibly by the Magisterium. The early Church fathers all argued against the heresies and heretics of their day, even though most of these heresies did not contradict any particular infallible magisterial pronouncement.
The infallible teachings of Tradition, Scripture, Magisterium are never open questions.
Whenever the Magisterium teaches, other than under Papal Infallibility, Conciliar Infallibility, or the Universal Magisterium, the teaching is non-infallible and non-irreformable. The non-infallible teachings are not necessarily entirely free from error; they allow for a limited possibility of error and reform. However, no error or set of errors in non-infallible teachings can ever reach to the extent of leading the faithful away from salvation.
Can. 750 §2. “Each and every thing which is proposed definitively by the magisterium of the Church concerning the doctrine of faith and morals, that is, each and every thing which is required to safeguard reverently and to expound faithfully the same deposit of faith, is also to be firmly embraced and retained; therefore, one who rejects those propositions which are to be held definitively is opposed to the doctrine of the Catholic Church.”
This type of truth is not explicitly, but implicit in Tradition or Scripture. These truths have a necessary connection with the explicitly revealed truths in the Sacred Deposit of Faith. The Magisterium is able to teach both explicitly revealed and implicitly revealed truths from Divine Revelation. And the faithful are required to adhere to those teachings, regardless of whether or not those teachings are explicitly found in Tradition or Scripture.
Can. 752 “Although not an assent of faith, a religious submission of the intellect and will must be given to a doctrine which the Supreme Pontiff or the college of bishops declares concerning faith or morals when they exercise the authentic magisterium, even if they do not intend to proclaim it by definitive act; therefore, the Christian faithful are to take care to avoid those things which do not agree with it.”
Can. 753 “Although the bishops who are in communion with the head and members of the college, whether individually or joined together in conferences of bishops or in particular councils, do not possess infallibility in teaching, they are authentic teachers and instructors of the faith for the Christian faithful entrusted to their care; the Christian faithful are bound to adhere with religious submission of mind to the authentic magisterium of their bishops.”
Can. 754 “All the Christian faithful are obliged to observe the constitutions and decrees which the legitimate authority of the Church issues in order to propose doctrine and to proscribe erroneous opinions, particularly those which the Roman Pontiff or the college of bishops puts forth.”
Non-infallible teachings of the Pope, the Bishops, or even individual Bishops are teachings of the authentic magisterial authority of the Church, and these teachings, too, require the adherence of the faithful. The type and degree of adherence for non-infallible teachings differs from those of infallible teachings. The former requires the religious submission of will and intellect (religious assent); the latter requires the full assent of faith (theological assent). However, assent is nevertheless required.
A theologian might faithfully dissent from a particular point within a non-infallible teaching, if he has a sound basis in the teachings of Tradition, Scripture, Magisterium. However, he should not be teaching this point as if it were uncontested truth, nor as if the position of the Magisterium carried no more weight than his own argument.
Unfortunately, it has become common for priests, theologians, and various Catholic commentators to ignore, doubt, cleverly re-interpret, substantially change, or supposedly refute, any number of non-infallible teachings by the Magisterium. If a teaching is not infallible, they speak and act as if there were no requirement whatsoever to adhere to the teaching, as if it were still an open question.
This type of behavior is sinful. It is possible that some persons are committing the sin of heresy by rejecting only what is non-infallible? Yes, it is possible. Usually, heresy is the sin of rejecting an infallible teaching. But anyone who rejects all or most non-infallible teachings, or who treats all or most non-infallible teachings as if there were no requirement of assent (as if entirely subject to doubt), is rejecting such a substantial portion of the teachings of the Faith as to constitute heresy. For heresy is that type of denial or doubt that undermines the essential teachings, the very foundation, of the true Faith.
Examples of this type of sin are found in those many moral theologians who treat the most basic principles of ethics, taught by the Magisterium in Veritatis Splendor and in the CCC (and in other magisterial sources) as if these were still a matter of dispute, or as if anyone could propose a new approach to ethics, which casts aside the three fonts of morality, and replaces them with some other basis. They treat intrinsic evil and the moral object as if the meaning of these terms were open questions. They make claims (such as that intention and circumstances can possibly change or constitute the moral object) that are directly contrary to definitive teachings of the Magisterium.
Other persons claim that the basis of morality as three fonts can be set aside to be replaced by virtue ethics, or an ethics based on relationships rather than acts, or some other new system of morality. They ignore the fact that Veritatis Splendor, the CCC, and other magisterial sources have definitively taught the three fonts of morality AND have clearly and definitively taught the meaning of each font.
But to many commentators, it is as if the Magisterium were either a mere advisor, as if they has as much teaching authority as the Magisterium does, as if the Magisterium were an annoyance, or even as if the Magisterium were a continual formidable opponent. Such persons who reject the teaching authority of the Church commit the sin of heresy and schism.
Which matters of faith or morals are open questions? Those question alone are open whose answers have not been definitively taught by the Magisterium, either infallibly or non-infallibly. Priests, theologians, and various online commentators are not free to contradict, ignore, or substantially change any teaching of the Magisterium.