Roberto Di Ceglie's Aquinas on Faith, Reason, and Charity begins by situating itself within a late last-century debate among Catholic philosophers as to the nature of ‘Christian philosophy’. That debate concerned whether faith only provides a motivation to philosophy or also necessarily involves changes to the discipline, imposing unique constraints upon or giving unique content to philosophy. The author wishes to endorse, defend, and develop in the current context of Thomistic scholarship the latter view (associated with Etienne Gilson) that philosophy changed substantially as a result of the encounter with Christianity. And he does this by proposing an epistemology that rests on grace.

Di Ceglie offers a perspective on which rationality is transformed when operating under the light of supernatural virtues. This perspective is advanced in criticizing many contemporary approaches to Thomistic faith. Di Ceglie has as his targets particularly Swinburne, the early Plantinga, and Kenny. He argues that these thinkers hold that faith is rational only to the extent that evidence for belief is available to the believer. He then rejects such views as overly reliant upon assumptions derived from Locke that faith consists in a species of assent to propositions, ignoring Aquinas’ claims that faith is a habit infused by grace and motivated by charity. Di Ceglie instead looks favourably upon the later Plantinga and Stump's construal of Aquinas as an externalist or reliabilist about justification, rejecting with Stump any broadly Cartesian internalist reading of Aquinas (31–32).

Yet Di Ceglie does not wholly embrace the externalist account. While appreciating Stump's mention of grace as the cause of faith and charity, Di Ceglie believes an externalist account of cognition fails to give the agent knowledge that their beliefs are justified. Di Ceglie claims that externalism requires reasoning to the fact that God created us with reliable cognitive faculties or that these faculties will operate properly in their intended environment. This cannot be done – Di Ceglie proposes – without employing as implicit premises beliefs about those same cognitive faculties in that reasoning:

Di Ceglie thus concludes that Stump and Plantinga's externalism is insufficient, because, without faith, the agent cannot believe with rational justification that their reasoning is reliable – there is no independent support for beliefs about the reliability of our reasoning faculties apart from faith.

In chapters 3–5, Di Ceglie develops an interpretation of Aquinas’ views on faith. He begins by showing that Aquinas holds that the certitude of faith is caused by grace rather than correlated with the strength of evidence available to the believer. In particular, Di Ceglie is interested in rebutting those views on which one must have good reasons for the existence of God accessible by natural reason before being able to believe in God through faith. He points out that, for Aquinas, the certitude of faith extends to belief in the existence of God, even though God's existence can be known philosophically as well (103–109). Faith is an effect of charity, he argues, so that what makes faith meritorious is that one's trust in and love of God motivates ‘steadfastly hold[ing] to their belief, however convincing contrary evidence might be’ (87). Di Ceglie takes this picture to undermine critiques of cognitive faith by relating our beliefs directly to our moral state and our relationship with God. But Di Ceglie's position also results in the position that faith without charity is not faith at all – it remains only ‘faith commonly so called’, which Di Ceglie identifies with the ‘faith of the demons’ referenced in Jas. 2:19 (123–124). Consequently, those in a state of mortal sin do not believe God or in God at all; they only believe things about God on the basis of reasons accessible to them. Di Ceglie claims that the formal object of lifeless faith is ‘the host of reasons for believing by “external persuasion”’ – and therefore that the ‘faith’ of sinners does not share a formal object with the faith of the believer (119). This also affects the certainty of the beliefs of those who are not in a state of grace, since their beliefs about God ‘will be based only on reasoning’ rather than, as with the believer, having a certainty proportionate to their love of God (128).

Di Ceglie defends this picture as having apologetic value. In responding to criticisms that believers are irrational or unable to engage honestly with their unbelieving epistemic peers, he underlines that faith serves to provide an orientation to objective research or investigation. Believers will want to confirm what they know by faith and will be more motivated to do so as their faith is motivated by love of God. A Christian philosopher will know God exists and therefore is motivated to search for a rational basis to demonstrate that to others without fear that their theoretical research could inadvertently undermine their religious beliefs. Believers will be more zealous for the truth than atheists or agnostics, since their research is motivated by love of God. Their faith also serves as a criterion according to which believers ‘reject outcomes that contradict divine revelation’ (152). Di Ceglie thinks this is compatible with objectivity, however, because faith is a product of grace and not reasoning. Thus, ‘this trust . . . cannot participate in the rational process’ (153). The believer is not wedded to any specific arguments for their beliefs and so, if their arguments fail or they encounter reasons to cease believing, they will merely ‘start researching anew from the beginning’ (153).

Di Ceglie concludes the book by recapitulating his central thesis that only faith in God's providence will give someone adequate justification for believing that their cognitive faculties are reliable. Believers believe in God not on the basis of any exercise of cognitive faculties but only as prompted by grace (150), giving them sufficient independent justification for their beliefs in the reliability of their faculties, as their belief in that reliability follows from what they believe about God by faith. He employs this epistemological claim as an apologetic argument against atheists and agnostics: a believer (unlike an atheist) will never be afraid that one's conclusions ‘may ever disprove beliefs that they maximally care about’ (162). Faith thus promotes reasoning, Di Ceglie concludes, in addition to motivating it and serving as a criterion for it. Since only the person with faith can have rational certainty that their reasoning is reliable and gives them motivation to be objective, the believer can criticize the reasoning of non-believers as relying upon irrational presumption that their faculties are reliable or as having no rational motive for objectivity in their enquiry. Only faith can give a non-circular subjective justification for anyone to believe in the reliability of their cognitive faculties – and faith is precisely what non-believers lack.

Di Ceglie's overall picture is one on which we cannot have rational certainty of the right sort in the articles of faith, in the existence of God, or even in the reliability of one's reasoning without grace and charity. Given the author's focus on Thomistic interpretation, Di Ceglie does not engage with any contemporary analytic literature concerning the nature of faith (no references to, for example, Kvanvig or Buchak, and only a passing reference to Howard-Synder in regard to other matters). Much of this discussion would probably resonate with Di Ceglie and provide him with resources for expanding his account. Further, Di Ceglie does not address systematic theological concerns, such as those conciliar claims made by the Catholic Church, for instance, that human beings can come to certainty about the existence of God from natural reason alone (Vatican I), or that the gift of faith remains in those who lack charity but have not sinned against faith specifically (Trent). While these claims do not affect the validity of an interpretation of Aquinas and are beyond Di Ceglie's stated aims, they would nevertheless merit addressing so that orthodox Catholics today may accept Di Ceglie's proposed interpretation as theologically reasonable.

Beyond these concerns of scope, questions might be raised about De Ceglie's epistemology. Di Ceglie operates mostly within Thomistic scholarship in advancing his own interpretation of Aquinas on faith. He does not outline his own working notion of epistemic justification, which raises some difficulties in understanding his position. Externalists such as Stump and Plantinga would straightforwardly reject the view that the believer needs to have arguments or evidence for their properly basic beliefs, and so do not require that believers have any arguments for properly basic beliefs if those beliefs are to count as having warrant or being justified. Di Ceglie's criticisms look like an internalist critique of Stump and Plantinga, because he seems to disagree that properly basic beliefs, at least concerning the reliability of one's epistemic faculties, can be justified without evidence or independent support accessible to the believer. Yet his own position is that the believer needs no arguments or evidence whatsoever for their beliefs to be justified when it comes to religious beliefs – faith in God alone is caused by grace alone, without any inferential support. There are then principled differences in accepting internalist criteria for the justification of properly basic beliefs but externalist criteria for the justification of religious beliefs.

More clarity on the reasons for this lack of symmetry in epistemic justification seems necessary in order to evaluate Di Ceglie's proposal. On the one hand, coming to an act of faith appears to involve use of our ordinary cognitive faculties, even though faith is caused by grace, and Di Ceglie's criticisms of externalism seemed to require that one has good non-circular reasons for believing that one's epistemic faculties are reliable. If faith literally has no basis in reasons that are accessible to the believer, or no non-circular reasons, then it appears as if faith is not rationally justified by Di Ceglie's own lights. We see this in Di Ceglie's account of the way in which believers are supposed to be rationally justified when they reject arguments that seem to undermine their faith. Yet it seems prima facie as if they do so on the basis of circular reasoning: for example, I know these arguments are false because God is reliable, and I know God is reliable because these arguments are false. It is difficult to evaluate Di Ceglie's proposal without clarity concerning, then, the asymmetrical burdens in justification of religious beliefs versus other properly basic beliefs.

On the other hand, given the wide scope of Di Ceglie's claims, it appears as if no belief is justified without faith and charity. If, as Catholic dogma teaches (viz. Trent), we cannot know with certainty whether we are in a state of grace, then it seems we could never in principle have certainty about the reliability of our cognitive faculties. The Tridentine claim, combined with Di Ceglie's account, would seem to undermine any apologetic use of the account of faith's rationality, since rational certainty and justification would be inaccessible to those without faith. Consequently, it would not seem possible to argue with unbelievers that they are being irrational or engage with them in epistemic criticism if (as Di Ceglie holds) the standards for that criticism derive from faith and are thus inaccessible to the unbelievers. Further, believers would not even have a shared rational basis for evaluating beliefs of other Catholics, if any are in a state of mortal sin. On both these fronts, more detail is necessary in order to understand Di Ceglie's proposal.

Roberto Di Ceglie's work will nevertheless be of interest to those who might be inclined to a less ‘intellectualist’ cognitive account of faith. His account shares features with non-cognitive accounts of faith, such as the emphasis on importance of moral character, motivation, or perspective, while preserving an integral place in faith for propositional assent. Finally, his exposition of Aquinas serves as an important corrective to an overly narrow vision of faith as mere assent to propositions about the existence of God, or to propositions on which demonstrative proof of the existence of God would be a necessary prerequisite for rational acts of faith.