A quote sadly (but necessarily) torn from a recent essay:
Note, however, I am setting aside the very important point that, in truth, we must go further and also speak theologically here, explaining how faith, synderesis, infused prudence, and the Spirit’s gift of counsel all interact. We do not have time, however, to add this complexity, though it is an important one (and, indeed, one that is too frequently forgotten). On this, see B.-H. Merkelbach, Summa theologiae moralis, 5th ed., vol. 2 (Paris: Desclée de Brouwer, 1947), no. 218: “Faith informs and elevates reason and synderesis, subordinating them to itself. Consequently, under the light of faith, synderesis is able to enunciate the first supernatural practical principles. And reasonably so, for supposing that faith teaches that God has elevated us to a supernatural end and that our ultimate good is only found in the beatific vision of God Himself, reason sees already that we must tend toward that end and that the ultimate good to be possessed in this manner must be loved in all of our acts. And do not say that synderesis does not have an idea of the supernatural end, for synderesis does not exist for conceiving ideas but, supposing these ideas, it sees and with ease enunciates their befittingness or unbefittingness.—St. Thomas does not expressly speak about supernatural conscience but everywhere says that the Major premise is placed in conscience by synderesis; however, he is not speaking only about the conscience of philosophers but also is speaking of the conscience of believers; [therefore, supernatural conscience enunciates its major premise by means of synderesis, though as elevated by faith]”(my translation)."