Vol. I, Book 1, Ch. 2 http://www.britac.ac.uk/pubs/dialogus/t1d1.html, as translated by John Kilcullen and John Scott (2003).
Dialogus (1494)
Context: It is on account of theology alone that any assertion whatsoever should be called catholic or heretical. For only an assertion which is consonant with theology is truly catholic, and only one which is known to be opposed to theology is known to be heretical. For if some assertion were found to be opposed to decrees of the highest pontiffs, or also of general councils or also to laws of the emperors, nevertheless, if it were not in conflict with theology, even if it could be considered false, erroneous or unjust, it should not be counted as a heresy.
William of Ockham: Assertion
William of Ockham was medieval philosopher and theologian. Explore interesting quotes on assertion.
Vol. I, Book 1, Ch. 2.
Dialogus (1494)
Context: The Holy Spirit through blessed John the evangelist makes a terrible threat against those who add anything to or take anything from divine scripture when he says in the last chapter of Revelations [22:18–9], "If any man shall add to these things, God shall add unto him the plagues which are in this book. And if any man shall take away from the words of the book of this prophecy, God shall take his part out of the book of life and out of the holy city, and from these things that are written in this book." We clearly gather from all these that nothing should be added to sacred scripture nor anything removed from it. To decide by way of teaching, therefore, which assertion should be considered catholic, which heretical, chiefly pertains to theologians, the experts on divine scripture.
You see that I have set out opposing assertions in response to your question and I have touched on quite strong arguments in support of each position. Therefore consider now which seems the more probable to you.
Vol. I, Book 2, Ch. 22 http://www.britac.ac.uk/pubs/dialogus/t1d2b.html, as translated by John Scott (1999)
Dialogus (1494)