Aquinas’s thought is often considered an exemplary balance between Christian faith and natural reason. However, it is not always sufficiently clear what such balance consists of. With respect to the relation between philosophical topics and the Christian faith, various scholars have advanced perspectives that, although supported by Aquinas’s texts, contrast one another. Some maintain that Aquinas elaborated his philosophical view without being under the influence of faith. Others believe that the Christian faith constitutes an indispensable component of Aquinas’s view; at (...) least when Aquinas focused on those statements that, though maintainable by mere reason, belong to the Christian revelation. In this essay I intend to show that the aforementioned perspectives can be reconciled on the basis of Aquinas’s concept of faith. If we do not limit ourselves to considering faith as the assent to the revealed truth, but also look at what leads the believer to assent—i.e., charity that unites the believer with God and is gratuitously conceded by God himself—then the relation between faith and reason appears to be twofold. On the one hand, the truths of faith cannot participate in the rational inquiry, because according to Aquinas faith lacks the evidence searched for by natural reason. On the other hand, since Aquinas holds that faith is the assent to the revelation due to the love for God that is granted by God himself, the believer will take faith as more certain than intellect and science, and the truths of faith will constitute the orientation and criterion of her/his rational investigation. The truths shall constitute orientation because the believer aims to confirm by reason what she/he already believes. They will also be criterion, because in case of a contradiction between rational arguments and revealed truths, reason must be considered mistaken and the rational investigation must start anew from the beginning. (shrink)