18 Moreover, the Angelic Doctor pushed his philosophic inquiry into the reasons and principles of things, which because they are most comprehensive and contain in their bosom, so to say, the seeds of almost infinite truths, were to be unfolded in good time by later masters and with a goodly yield. And as he also used this philosophic method in the refutation of error, he won this title to distinction for himself: that, single-handed, he victoriously combated the errors of former times, and supplied invincible arms to put those to rout which might in after-times spring up. Again, clearly distinguishing, as is fitting, reason from faith, while happily associating the one with the other, he both preserved the rights and had regard for the dignity of each; so much so, indeed, that reason, borne on the wings of Thomas to its human height, can scarcely rise higher, while faith could scarcely expect more or stronger aids from reason than those which she has already obtained through Thomas.
Source: Aeterni Patris (Vatican.va)