One of the most discussed texts of the First Vatican Council (1869-1870) is the first paragraph of Dei Filius, 2. In the Latin text this paragraph is in fact a single sentence. It is especially the first clause that interests people. There we find this statement (to which I have added a period):
Eadem sancta mater Ecclesia tenet et docet, Deum, rerum omnium principium et finem, naturali humanæ rationis lumine e rebus creatis certo cognosci posse.
[The same holy mother Church holds and teaches that God, the principle and end of all things, can be known with certainty by the natural light of human reason from created things.]
The Council fathers then go on to cite Romans 1:20 as their proof text. There are those (notoriously, Karl Barth) who think that this is not the right way to read this passage in Romans. I am not concerned with that debate at the moment but only with how to interpret the brief passage from Dei Filius.
It is customary in the Catholic tradition to understand that those things that “unaided” reason can know about God are his existence and nature; the Trinity, Incarnation, etc. cannot be known by reason without revelation. So, it is natural to assume that the Council has the former in mind when it speaks of knowing God, the principle and end of all things, by the natural light of reason. This assumption is not controversial.
However, some interpreters of the document have argued — we will leave aside their motivations since they’re not particularly important here — that the above statement of Dei Filius does not exclude the possibility that supernatural revelation was necessary first to inform us about the existence and nature of God as long as it is acknowledged that once the cat is let out of the bag, so to say, we are now able to see by reason’s own power that the created order points to this God. The idea seems to be that it was always possible in fact to know God through the created order but that we were unable to grasp this (and could never have grasped it) until revelation pointed it out to us. And these commentators indeed hold that this is how things stand.
I think that there are a few problems with this interpretation of the text in question but let me just take up one in this post, the one that looks to me most obvious, that is, that the rest of the document appears to exclude this way of reading the text. The paragraph that follows our text runs like this:
Huic divinæ revelationi tribuendum quidem est, ut ea, quæ in rebus divinis humanæ rationi per se impervia non sunt, in præsenti quoque generis humani conditione ab omnibus expedite, firma certitudine et nullo admixto errore cognosci possint.
[It is indeed from this divine revelation that those divine things that are not of themselves inaccessible to human reason can, even in the present condition of the human race, be known by all easily, with firm certitude, and with no admixture of error.]
Again, we can assume that “rebus divinis humanæ rationi per se impervia non sunt” refer to God’s existence and nature. We are instructed that these divine things that are in principle naturally knowable were nevertheless revealed and that this places them in everyone’s reach (i.e., everyone who believes). A note in Denzinger’s Enchiridion Symbolorum (40th ed., P. Hünermann) suggests Summa Theologiae, I, 1, 1 as a source of this teaching. There Aquinas writes:
Ad ea etiam quae de Deo ratione humana investigari possunt, necessarium fuit hominem instrui revelatione divina. Quia veritas de Deo, per rationem investigata, a paucis, et per longum tempus, et cum admixtione multorum errorum, homini proveniret, a cuius tamen veritatis cognitione dependet tota hominis salus, quae in Deo est. Ut igitur salus hominibus et convenientius et certius proveniat, necessarium fuit quod de divinis per divinam revelationem instruantur.
[Even as regards those truths about God which human reason could have discovered, it was necessary that man should be taught by a divine revelation; because the truth about God such as reason could discover, would only be known by a few, and that after a long time, and with the admixture of many errors. Whereas man’s whole salvation, which is in God, depends upon the knowledge of this truth. Therefore, in order that the salvation of men might be brought about more fitly and more surely, it was necessary that they should be taught divine truths by divine revelation.]
Interestingly, Aquinas says here that that these truths about God that are naturally knowable do not absolutely require divine revelation since some people are capable of grasping them without supernatural assistance (elsewhere Aquinas even notes the fact and not just the possibility), even if these people are few. Revelation is needed only to make them more generally known.
Aquinas’s way of understanding these naturally knowable divine truths is plainly at odds with those who think that these truths must first be revealed before reason can investigate them on its own and interpret Dei Filius as permitting this view. But if Dei Filius takes Aquinas’s line, this view is excluded.
Returning to the text of Dei Filius we find that the very next sentence says:
Non hac tamen de causa revelatio absolute necessaria dicenda est, sed quia Deus ex infinita bonitate sua ordinavit hominem ad finem supernaturalem, ad participanda scilicet bona divina, quae humanae mentis intelligentiam omnino superant.
[It is not because of this that revelation is said to be absolutely necessary but because God from his infinite goodness ordained man to a supernatural end, namely, to sharing in the good things of God, which utterly surpasses the understanding of the human mind.]
Apparently, then, the Council does take Aquinas’s line, although it does not put it in the same way. We are told that “this” (hac) is not the reason why divine revelation was absolutely necessary. “This” refers back to the knowledge of divine things that are naturally accessible to reason. The point that the Council fathers are making is that revelation is not absolutely necessary for such knowledge (precisely what some interpreters of Dei Filius deny). Revelation is necessary, rather, because salvation requires knowledge of truths that are beyond reason’s natural power.
In light of these words of the Council I don’t see how it can be supposed that divine revelation is needed to point us to “naturally knowable” truths about God’s existence and nature.