Diggerdomer, canon 752 speaks of the situation where the College of Bishops may wish to speak on an issue of faith and morals without exercising infallibility. It says that in such cases, religious submission is required but not the assent of faith. The following is quoted from the
romancatholicism.org site:
Paul VI had already stated in his address concluding the Council the day before that the Council had not “wish[ed] to issue extraordinary dogmatic pronouncements” and therefore was not infallible; Felici went on to explain that Paul VI was making the Council a matter of religious submission, which is the assent given to non-infallible material, as we shall see.
“And last of all it was the most opportune, because, bearing in mind the necessities of the present day, above all it sought to meet the pastoral needs and, nourishing the flame of charity, it has made a great effort to reach not only the Christians still separated from communion with the Holy See, but also the whole human family. …] We decided moreover that all that has been established synodally is to be religiously observed by all the faithful, for the glory of God and the dignity of the Church and for the tranquillity and peace of all men. …] Given in Rome at St. Peter’s, under the [seal of the] ring of the fisherman, Dec. 8, on the feast of the Immaculate Conception of the Blessed Virgin Mary, the year 1965, the third year of our pontificate.” (In Spiritu Sancto, Walter M. Abbott, SJ, The Documents of Vatican II, pp. 738-9)
Paul VI established at the Council’s end that “all that has been established synodally is to be religiously observed”. The 1983 Code of Canon Law distinguishes the matter of religious submission from infallible, definitive teaching.
“Can. 752. While the assent of faith is not required, a religious submission of intellect and will is to be given to any doctrine which either the Supreme Pontiff or the College of Bishops, exercising their authentic magisterium, declare upon a matter of faith or morals, even though they do not intend to proclaim that doctrine by definitive act. Christ’s faithful are therefore to ensure that they avoid whatever does not accord with that doctrine.”
So, “religious submission” is given when the Pope, either alone or with his bishops in a council, does not intend to “proclaim doctrine by a definitive act”: therefore the matter of religious submission is not infallible, which is why it does not require “the assent of faith”.
Me again. We are not required to believe non-infallible teachings of an ecumenical council because they are non-infallible. Being non-infallible, they are fallible, and seeing as they can be in error, it would be wrong for the Church to bind Catholics to believe teachings that can be in error. This would be binding us to the mind of men, not to the mind of Christ. For this reason, we are required to give religious submission to non-infallible teachings, submission of mind and intellect so that we do not seek to rebel against the Church and don’t reject the authority of the council, but we are not required to yield these teachings the “assent of faith,” believing whatever the council says. This could risk binding the faithful to believing error, something the Church does not do.
We
are required to give the assent of faith to all defined dogmas and to the whole of the Church’s deposit of faith preserved in her Sacred Tradition.