When the Pope or a Council or the Universal Magisterium teaches infallibly, the faithful are required to give the full assent of faith (what I term ‘sacred assent’). Infallible teachings of the Magisterium are guaranteed by the Holy Spirit to be without error. But such teachings are not merely error free. Statements such as ‘Two plus two equals four,’ and ‘The sky is blue’ are error free. Infallible teachings of the Magisterium are on important matters of faith, morals, or salvation. A triviality cannot be infallibly defined, even if all agree that the point is true. The gift of infallibility is important to our salvation, and so we are required under pain of heresy to believe what is taught.
However, a faithful Catholic may disagree, to a limited extent, with the interpretation of an infallible teaching that prevails among theologians or among the laity. All infallible teachings (dogmas) require interpretation, in other words, the use of the faculty of reason is necessary so that we can understand to what we must assent. A faithful Catholic might have a somewhat different interpretation of an infallible teaching than other Catholics. But no interpretation can change an infallible teaching from one assertion into another. We may ask how are we to understand this teaching, but we may not use ‘interpretation’ to change a teaching that we dislike into one we like.
Non-infallible teachings of the Pope require a different type and degree of assent. They require the religious submission of will and intellect (what I term ‘ordinary assent’). The ordinary teachings of the Pope, of an Ecumenical Council, and even of the body of Bishops united with the Pope (when that teaching is not presented to the faithful as definitively to be held), are non-infallible and subject to a limited possibility of error. But if such teachings can err, then why should we be required to believe them? Just as the infallible teachings are on matters pertaining to faith, morals, and salvation, so also are the non-infallible teachings on the same subject. And the errors that are possible never reach to such an extent as to lead the faithful away from the path of salvation. So the Church can require us to believe that which is helpful to salvation and which cannot endanger our salvation, despite some possibility of error.
But in the case of non-infallible teachings, the faithful can faithfully dissent, to a limited extent. For God who is Truth never requires His children to adhere to any falsehood. But the limit of dissent is the same as the limit of possible error. Furthermore, since non-infallible teachings are of the Magisterium teaching from Sacred Tradition and Sacred Scripture, as well as from natural law, mere reason is not sufficient to constitute a basis for licit dissent. The dissent must be limited, and must be based on Tradition, Scripture, and/or other teachings of the Magisterium.
The theological opinions of a Pope, expressed in a sermon, or in a general audience, or in a work of private theology, are not acts of the Magisterium. All are free to disagree. However, even reason itself requires that a reasonable person not disagree with any assertion without some basis, and further requires that one not disagree with an assertion by a person who has knowledge in a particular field without a substantial basis.
The decision of the temporal authority of the Pope are fallible. The Pope can err in his decisions about how to govern the Church, about rules and rulings in particular cases, about temporal matters of prudential judgment. However, the Church is indefectible, and so this type of decision — though it is neither an infallible nor a non-infallible teaching — can never lead the Church away from the path of salvation.
A faithful Catholic may disagree with the Pope on whether a particular war is a just war, or whether a nation should go to war in one case or another, or whether a particular nation or state should have the death penalty, or should exercise it in a particular case. This type of decision is of the prudential order. But the dissent of a faithful Catholic from a judgment of the prudential order of a Pope should always have some substantial basis in reason and temporal facts, and must always be consistent with the teachings of Tradition, Scripture, Magisterium.