Encyclicals are authoritative, teaching documents. While they may or may not contain explicit infallible terminology; they may reiterate infallibly taught doctrines. And even if they do not do that, they still require an inward assent. *Lumen Gentium * 25 says “This religious submission of mind and will must be shown in a special way to the authentic magisterium of the Roman Pontiff, even when he is not speaking ex cathedra; that is, it must be shown in such a way that his supreme magisterium is acknowledged with reverence, the judgments made by him are sincerely adhered to, according to his manifest mindand will. His mind and will in the matter may be known either from the character of the documents, from his frequent repetition of the same doctrine, or from his manner of speaking.”
However, when the Pope speaks “ex cathedra, that is when, in the exercise of his office as shepherd and teacher of all Christians, in virtue of his supreme apostolic authority, he defines a doctrine concerning faith or morals to be held by the whole Church” (First Vatican Council 1869-1870). “These doctrines require the assent of theological faith by all members of the faithful. Thus, whoever obstinately places them in doubt or denies them falls under the censure of heresy, as indicated by the respective canons ofthe Codes of Canon Law.” (
Doctrinal Commentary on Concluding Formula of the Professio fidei)
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