When I recently asked this question, a discussion ensued that has prompted me to lay out an argument against the position in which two claims are simultaneously held to be true: (1) some (but not all) Church councils are authoritative, and (2) there is no sacramental magisterial authority.
My argument begins by raising a question for the person holding that position.
(Q1) On what grounds does one determine which councils are authoritative?
For the person holding this position, there seems to be only one available answer to that question: Those councils are authoritative that agree with Scripture. But this answer just pushes us back to a further question:
(Q2) Agree with Scripture according to whom?
At that this point, the person holding this position can reply by appealing either to another council, to the Holy Spirit, or to his own interpretation of Scripture. Let's consider each of these three in turn.
First, if the person appeals to another council, the original question (i.e. Q1) applies to his determination of the authority of that council as well. So this reply simply pushes the question back; it does not answer the question. So this reply is not an option.
Second, if the person appeals to the Holy Spirit, this too pushes the question back to a further question: According to whose determination of what the Holy Spirit is saying? The answer to that question cannot be "another council", since again, that too would just push back the question. Nor can the answer be "the Holy Spirit", because that too would just push back the question. Nor can the answer be "the Scriptures", because the appeal to the Holy Spirit was the answer to Q2. So to appeal to Scripture here would be to fall into circular reasoning. The circularity would look like this: According to whose interpretation of Scripture? The Holy Spirit's. According to whose determination of what the Holy Spirit is saying? The Scripture's. According to whose interpretation of Scripture? The Holy Spirit's. .... So this reply too is not an option.
Third, he can appeal to his own interpretation of Scripture. This amounts to the notion that those Church councils are authoritative that agree with one's own interpretation of Scripture, and that those Church councils are not authoritative that do not agree with one's own interpretation of Scripture. But this completely undermines the authority of any council, for the very nature of authority is not something to which we are subject only when in agreement with it.
But there seem to be no other possible answers to Q2. If there are no other answers to Q2, then since the first two replies to Q2 do not answer the question, the person holding this position is by default treating the third reply as the answer to Q2. This implies that the person holding this position is involved in a contradiction. On the one hand he is claiming that some Church councils are authoritative. But on the other hand, by picking as 'authoritative' only those councils that agree with his own interpretation of Scripture he is acting as though there is no such thing as ecclesial authority. His position would not involve a contradiction if when he says "some councils are authoritative", what he means by 'authoritative' is "in agreement with my interpretation of Scripture". In other words, he can avoid the contradiction by making explicit that he is using the term 'authoritative' in a way that is contrary to its ordinary sense. But if he retains the ordinary sense of the term 'authoritative', then his position involves a contradiction. This implies that if the ordinary sense of the terms is retained, claim (1) and claim (2) are contraries, i.e. they cannot both be true.
Now, the common rejoinder to this sort of argument is a tu quoque: you too. The claim is that in the process of becoming Catholic or Orthodox, a person must use his own reason and private judgment, and that he too just chooses his ecclesial authority according to his own interpretation of Scripture. So he too faces this same contradiction of claiming that there is ecclesial authority but in fact determining who counts as ecclesial authority by seeing who agrees with himself. But there is a qualitative difference between the two cases. The person who discovers sacramental magisterial authority does not do so by determining who agrees with himself. He does so by finding out (often from the fathers) that the early Church was always governed by sacramental magisterial authorities, and then tracing forward the sacramental line of apostolic succession through the history of the Church to the present. So he is not choosing his ecclesial authority based on whether they agree with his own interpretation of Scripture; he is choosing his ecclesial authority based on whether they are the *sacramental* successors of the Apostles. A sacramental criterion of ecclesial authority is in that way qualitatively different from a doctrinal (i.e. formal) criterion. Sacramentality cannot be reduced to form. And that is why sacramental authority is not properly discovered (as such) by doctrinal agreement with the individual. So the person in the process of becoming Catholic or Orthodox is not susceptible to the tu quoque charge, because his manner of seeking out ecclesial authority is not incompatible with the existence of that authority, whereas the person holding (1) and (2) and determining which councils are authoritative by judging them according to his own interpretation of Scripture is seeking out ecclesial authority in a manner that is incompatible with the existence of actual ecclesial authority.
"Let unity, the greatest good of all goods, be your preoccupation." - St. Ignatius of Antioch (Letter to St. Polycarp)