Commentaria in Primam Partem Summae Theologiae

The title is clear. – In the body he does two things: first, he teaches in general in what matter of faith it is permissible or not permissible to hold contrary opinions; second, he answers the question¹.

II. As to the first point, he posits a twofold class of things pertaining to the faith: namely, directly and indirectly. Concerning the first class he says that to hold a false opinion is heresy, especially when joined with pertinacity. – Concerning the second class, however, he says two things. First, that before something contrary to the faith is considered, or determined, holding a false opinion about it is not heresy, especially without pertinacity. The second is that an error of this kind after its manifestation, or the Church's determination, is heresy. – And from these it is deduced as a corollary that many things today are reckoned heretical, etc.

III. Note here that for the notion of heresy in itself, it suffices that there be error in matters of faith; but for the formal notion of a heretic, something further is required beyond this, namely pertinacity. And therefore in the text, by way of addition, there is appended, whether pertinacity be present or absent.

Again, in the second kind of case, when a determination of the Church is lacking, it is not held to be manifest that something contrary to the faith follows from some position, on the ground that many doctors believe thus, while others hold the opposite. Hence in cases of this kind, those who hold a false opinion are excused not only from heresy but also from sin, since, according to their own degree, as far as they know, they judge themselves to be following the more reasonable way, with reverence for the Church preserved.

IV. As to the second point², the responsive conclusion is that, although to hold contrary opinions about the notions would be contrary to the faith if there were nothing in them, or if they were not considered. – And it is proved: because the notions are of the second kind³.