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Thomas Aquinas on Non-Theological Faith

Published online by Cambridge University Press:  29 February 2024

Catherine Peters*
Department of Philosophy, Loyola Marymount University, Los Angeles, CA, USA
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The majority of studies on ‘faith’ (fides) in the thought of Thomas Aquinas consider it in a religious or theological context: fides as the theological virtue by which one assents to the truths of divine revelation. The focus on theological faith is appropriate, given its central importance as a theological virtue, but this is not the only sense of fides that Thomas identifies. The present study investigates two non-theological senses formulated in his commentary on the De Trinitate of Boethius: first, fides as the proximate cause of assenting to principles within a given science (‘epistemic faith’) and, second, fides as an indispensable element of society (‘societal faith’). These senses have been largely overlooked in secondary literature but, I argue, might help to dispel mischaracterizations of faith as fundamentally unreasonable.

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The majority of studies on ‘faith’ (fides) in the thought of Thomas Aquinas consider it in a religious or theological context. That is, fides as one of the three theological virtues by which one assents to the truths of divine revelation.Footnote 1 Unquestionably, Thomas’ presentations of theological fides are extensive, detailed, and rich. While focusing on theological fides is appropriate – given the central importance of faith as a theological virtue – such concentration can sometimes suggest a distance between theological certainty and other human forms of knowing. One example of an apparent disparity between theological and natural investigations concerns the role of authority. In theology, one accepts revealed truths on the basis of divine authority and such arguments are the strongest. In human disciplines, by contrast, arguments from authority are the weakest form of argument.Footnote 2 This divergence might lead one to regard theology as an instance of fideism, a forgoing of rational inquiry to make room for religious belief on the basis of believed authority. In such a conception of theology, faith becomes independent of reason, if not even unreasonable. Thomas himself never endorsed such a separation of faith and reason, of course, but claiming that faith may be reasonable now often calls for defense.

In the present study, I propose such a defense by considering two non-theological senses of fides as found in Thomas’ commentary on the De Trinitate of Boethius. The first, which I shall call ‘epistemic faith’, refers to faith within scientific practice. The second, which I shall call ‘societal faith’, refers to the function of faith within society. In contrast to the abundant treatments of theological faith, consideration of these two non-theological senses of fides is sparse.Footnote 3 The present study intends to show the importance of these non-theological senses, both in themselves and as entrées to theological faith. These two senses of fides can remind us that faith is a critical element in human life even outside the sphere of religious belief and, consequently, they suggest that faith may be reasonable. Recognizing the importance and pervasiveness of fides allows one to recognize, I propose, that it is not so much a question of whether one has faith as it is in what one has faith.

1. Fides in the super boetium de trinitate

Though unfinished, Thomas’ commentary on the De Trinitate of Boethius contains an abundance of riches.Footnote 4 Question V, in particular, has occupied a significant place in Thomistic scholarship insofar as it contains explicit and extensive treatment of how different sciences pursue their investigations and how certain natural sciences (i.e., physics, mathematics, and metaphysics) relate to theology. Thomas makes clear from the outset that he accepts the generally Aristotelian conception of a ‘science’ as an organized body of investigation aimed at arriving at demonstrated truths about a given subject.Footnote 5 Theological demonstrations – like all demonstrations – proceed from principles, and so Thomas must consider whence these principles come. In natural sciences, principles are ultimately acquired by intellectus, the culminating point of human cognition by which one grasps universals within sensed particulars. In theological science, principles are acquired by fides. Footnote 6 As Thomas explains ‘as the principle of our cognition is naturally the knowledge of created things, obtained by means of the senses, so the principle of supernatural cognition is that knowledge of First Truth conferred upon us, infused by faith’.Footnote 7 Within his view of the scientific nature of theology, fides functions as a kind of intellectus insofar as this allows one to accept the first principles of theology.Footnote 8

2. Non-theological fides

Faith is, for Thomas, first and foremost a theological virtue, that by which we assent to the truths of divine revelation. But fides is neither only nor always concerned with theology or religious belief. In his De Trinitate commentary, for instance, Thomas references two non-theological senses of fides. Let us consider each in turn.

2.1 Epistemic faith

Recall that, for Thomas, all sciences (both theological and natural) depend on principles. The principles of natural sciences are, ultimately, grasped by intellectus and originate in sense experience. Importantly, however, while maintaining that natural sciences are ultimately empirical, Thomas does not insist that each science must be directly traced back to sense experience. On the contrary, he reminds us that, even ‘in those sciences handed down to us by human tradition, there are certain principles in some of them which are not universally known, but which presuppose truths derived from a higher science’.Footnote 9 In other words, a given science can accept principles from another science. While intellectus is always the ultimate cause of accepting scientific principles, it is often fides which serves as a proximate cause.Footnote 10 Put another way, we often accept principles on the basis of a kind of faith, not because of direct experience or insight. This is the kind of faith which I call ‘epistemic’.Footnote 11

Thomas suggests this sense of fides as a proximate cause of accepting scientific principles in Super Boethium De Trinitate, q. 2, article 2. This article concerns whether it is possible for there to be a scientia of theology, if theology is grounded in faith.Footnote 12 There he explains how theology proceeds from the principles of a higher science (namely the scientia of God and the blessed) but is still demonstrative insofar as these truths are accepted as principles and allow further demonstrations.Footnote 13 While replying to an objection, Thomas argues that faith concerns the principles of science, but not its demonstrations. The dependence on principles for demonstration is not unique to theology, he maintains, because ‘in any science whatever there are certain things that serve as principles, and others as conclusions. Hence the reasoning process set forth in the sciences precedes the assent given to a conclusion, but follows upon assent to principles, since it proceeds from them’.Footnote 14 In theology, these principles are the articles of faith. These must be accepted through faith but, once accepted, they serve as principles of theological demonstrations. Thomas continues to draw parallels between the science of theology and other sciences as follows:

Even in those sciences handed down to us by human tradition, there are certain principles in some of them which are not universally known, but which presuppose truths derived from a higher science, just as in subordinate sciences certain things taken from superior sciences are assumed and believed to be true; and truths of this kind are not per se nota except to the higher knowers.Footnote 15

Aristotle’s account of how sciences can be related to one another is clearly in play. Though sciences are specified by their subject matter (biology differs from chemistry, for example, because they consider different subjects), Aristotle does not separate one from all others. He first hints at the possibility of relating one science to another in Posterior Analytics I, 7 when stating that there can be a crossover between sciences if their demonstrations are ‘related as subordinate to superior (e.g. as optical theorems to geometry or harmonic theorems to arithmetic)’.Footnote 16 Aristotle elaborates on this suggestion in Posterior Analytics I, 13, where he explains that there are two ways that distinct sciences can stand in relation to one another. One way is when a science deals, in part, with the subject of another science (for example, botany deals with part of biology, but not all of it). In his commentary, Thomas sets aside the relationship of ‘part to whole’ and focuses on ‘subalternation’.Footnote 17 This occurs when a higher science possesses a demonstration for something that a lower science accepts as a non-demonstrated fact.Footnote 18 In such a relation, a ‘lower’ science accepts, as its principles, conclusions that may be demonstrated in another science.

In the Super Boetium De Trinitate passage quoted above, Thomas draws no distinction that separates, say, theology and philosophy from physics and mathematics. The sciences ‘handed down to us by human tradition’ include any area of investigation that follows the canon of the Posterior Analytics. Though ultimately interested in understanding the nature of theology, Thomas reminds us that subordination, in itself, does not rule out the possibility of attaining knowledge (scientia). A subordinate science might receive principles from a higher science, but these principles are nonetheless certain. In this way, both the higher subordinating and lower subordinated science can mount demonstrations.

While intellectus is the starting point of a science insofar as it allows us to grasp the indispensable principles of demonstration, Thomas soon turns to make a comparison and distinction between intellectus and fides. It is here that Thomas indicates a non-theological function of faith: faith as the proximate cause of grasping scientific principles.

Intellectus is always the first principle of any science (scientiae), but not always the proximate principle; rather, it is often fides which is the proximate principle of a science, as is evident in the case of the subordinate sciences; since their conclusions proceed from faith in truths accepted on the authority of a superior science as from a proximate principle, but also from the understanding of scientists in the superior field who have intellectual certitude of these created truths as from their ultimate principle.Footnote 19

Intellectus is that by which we grasp first principles. As such, it provides the ultimate grounding for all scientific investigations whatsoever. But not all sciences employ first principles; some, such as subordinate sciences, use proximate principles. A subordinate science accepts principles from a higher science, where these principles are ultimately grasped non-demonstratively through intellectus. But the subordinate science assumes these principles in order to mount its own demonstrations. If a subordinate science was not able to assume these principles, then each science would need to be a first. In other words, all principles would need to be directly received through intellectus, not received from another science.

So, for example, in this view of scientific practice, a psychiatrist would not be able to implement the conclusions of, say, biology or chemistry in practicing her medicine qua psychiatrist but rather would have to seek unmediated principles through intellectus. In other words, she would need to investigate the first principles of biology or chemistry herself before employing them in her practice. Aware that such recourse is neither theoretically nor practically necessary, Thomas maintains that fides can serve as a proximate cause of accepting principles. Thus, continuing my example, a psychiatrist need not herself perform the requisite chemical experiments needed to determine the nature and efficacy of a drug but can, instead, accept the findings of chemistry and implement them in her treatments.Footnote 20 This acceptance of principles on the basis of fides, one should note, does not thereby result in a loss of certitude.Footnote 21 Accepting a principle ‘on faith’ in this way does not mean that one does so ignorantly or naively. Subordinate sciences, for Thomas, in order to be subordinate, are dependent, but they are not thereby dubitable. Their certitude is derived from the certitude of the subordinating science, which itself is traced to intellectus. Faith, thus, can serve as a proximate cause of accepting principles and, arguably, makes the interchange between different scientific fields possible.

A little later, also in the Super Boetium De Trinitate, Thomas returns to the issue of fides and scientific practice. While his earlier concern was with the acceptance of principles, here he considers the process of scientific investigation. Keeping in mind that learning requires pre-possessed knowledge of some sort, he states that:

it is needful for us even at first to have some notion of those things that are most knowable in themselves; but this cannot be except by believing (credendo). And this is evident even in the order of the sciences; since that science which is concerned with highest causes, namely, metaphysics, comes last in human knowledge; yet in sciences that are preambles to it there must be supposed certain truths which only in it become more fully known therefore every science has some suppositions that must be believed in order to carry on the process of learning.Footnote 22

Though still concerned with the role of fides in science, one sees a difference in focus: now Thomas is treating how one, in fact, must accept on faith (credere) some truths if one is to pursue further investigation. In both instances, though, the role of faith concerns the possession or acquisition of scientific knowledge. In other words, they are two aspects of epistemic fides.

2.2 Societal faith

The second, less-often invoked, non-theological use of fides concerns the role of faith within a given society. Importantly, by this sense of faith, Thomas does not mean some sort of natural religiosity or human proclivity to cultic practice. Instead, the foundation for this sense of fides is his understanding of human dependency on each other within society. Thomas explains that ‘without faith human society cannot be preserved’ because it is indispensable, within a society, that ‘one man believe in the promises of another and in his testimony and the like, for this is necessary if they are to live together; therefore faith is most necessary for mankind’.Footnote 23 It is this kind of faith which I call ‘societal’.

Immediately after explaining how fides is somewhat akin to intellectus, scientia, and opinio, Thomas observes that fides, like opinio, deals at times with matters that seem in themselves dubitable (such as another person’s attestations). But, because society is built upon the relation of one person to another, there must be a way to give credence to each other:

since among men dwelling together one man should deal with another as with himself in what he is not self-sufficient, therefore it is needful that he be able to stand with as much certainty on what another knows, but of which he himself is ignorant, as upon the truths which he himself knows. Hence it is that in human society faith is necessary in order that one man give credence to the words of another, and this is the foundation of justice, as Tullius says in his book, De Officiis.Footnote 24

While Thomas will devote the rest of his attention in this question to the importance of theological faith, here he is focused on societal fides. Inspiration for associating faith with justice is found in Cicero, but it is important to note that neither Thomas nor Cicero depends on an explicitly theological source for this sense of fides. For both thinkers, fides is indispensable insofar as human beings are, by nature, social animals.

Thomas’ references to societal fides are not limited to the De Trinitate commentary. The importance of social veracity becomes yet more clear in his treatments of the virtue of ‘truth’ in the Summa Theologiae. As he insists there,

Since man is a social animal, one man naturally owes another whatever is necessary for the preservation of human society. Now it would be impossible for men to live together, unless they believed one another, as declaring the truth one to another. Hence the virtue of truth does, in a manner, regard something as being due.Footnote 25

Thomas repeats this claim later and argues that, given human nature, we have certain needs.Footnote 26 Inasmuch as we are imperfect and dependent beings, we naturally need to live in society with others. But without this kind of fides, society itself would be impossible to establish or maintain. Though referenced sparingly in the De Trinitate commentary, societal fides, thus, gives important insight into Thomas’ view of human nature and society.Footnote 27 In closing, I would also suggest, given that the very existence of a society depends on fides, that we should be more concerned with who and what we believe rather than attempting to banish faith from the public sphere.Footnote 28

2.3 ‘Testimonial justification’

These two non-theological senses of fides yield insight into Thomas’ view of scientific practice and human society. Given the importance of these areas of life, it is perhaps surprising that these senses have been, thus far, largely overlooked. A notable exception to this general tendency is Mathew Kent Siebert’s study, ‘Aquinas on Testimonial Justification: Faith and Opinion’.Footnote 29 In this study, Siebert draws on the De Trinitate commentary to offer ‘the first detailed interpretation and reconstruction of Aquinas’s account of testimonial justification’.Footnote 30 In his treatment, Siebert identifies three distinct sources for testimony: experts, peers, and teachers.Footnote 31 Expert testimonial justification consists of ‘a vertical epistemic division of labor, extending from experts down to those who trust them’, while peer testimonial justification refers to a societal need which ‘often requires us to act on what other people know, when not in a position to verify something for ourselves’.Footnote 32 Teacher testimonial justification is needed for learning because, Siebert reminds us, students must rely on the knowledge of their teacher if they are to progress in knowledge.Footnote 33 Each of these areas is an instance of someone (expert, peer, or teacher) transmitting something to another (a non-expert, a peer, or a student).

Siebert’s emphasis on the importance of testimony is well-placed but, at times, seems to equate non-theological fides and testimony.Footnote 34 What I have called societal faith clearly, it seems, concerns testimony: Thomas himself refers to the ‘testimony’ (testimoniis) of someone when introducing this sense of fides. Footnote 35 What is less clear, however, is that epistemic fides is also, always and only, a matter of testimony. Siebert argues that, for Thomas, ‘some of the preexisting knowledge required for learning a science must be testimonial’.Footnote 36 As he explains,

[Thomas] appeals to the Aristotelian ordering of the sciences, on which metaphysics is the most fundamental but also the most obscure. Similar considerations apply to contemporary natural science, in which physics is the most fundamental but at the same time arguably the most difficult to understand. Someone setting out to study physics would not get very far without some direction on the basic principles of force, motion, and matter, as physicists today understand them. The faith of a student, unlike that of nonexperts in a vertical epistemic division of labor, is a provisional faith, supporting one’s education until one is an expert oneself, and in the ideal case one comes to understand why the principles one accepted at the beginning of one’s education are true.Footnote 37

While Thomas does distinguish between the ‘knowledge’ of a student and the ‘knowledge’ of an expert, such distinction does not answer the question of whether epistemic fides reduces to testimony.Footnote 38 To answer this question, it is critical to understand what is meant by ‘testimony’.

Some maintain that testimony is, always and fundamentally, inter-personal. Paul Faulkner, for instance, argues that ‘the fact that what is presented-as-true does come from another person is a distinguishing feature of testimony’.Footnote 39 Taken in this way, the inter-personal element is indispensable in differentiating between testimony and other modes of acquiring belief or knowledge. Even those who advocate a broader understanding of ‘testimony’ consistently return to the personal dimension of such communications.Footnote 40 Granted, the testimony of societal fides certainly seems to be inter-personal. What is at issue now is whether epistemic fides is, similarly, fundamentally testimonial and, if so, essentially inter-personal.

Siebert’s underlining of the testimonial aspect of scientific practice emphasizes the mode of transmitting scientific truths. But Thomas’ account of subalternate science – the background for what Siebert calls ‘expert testimonial justification’ – does not focus on the mode of transmission so much as it does on the relation between ‘higher’ and ‘lower’ sciences. Thomas maintains that both ‘higher’ and ‘lower’ sciences can formulate demonstrations (inasmuch as each kind of science possesses principles) and refers to these demonstrations as propter quid and quia, respectively.Footnote 41 While there are a variety of ways to distinguish ‘higher’ (propter quid) demonstrations from ‘lower’ (quia) demonstrations, the way of most relevance to the present study concerns demonstrations from mediate or immediate principles:

one way that scientific knowledge quia differs from propter quid is that it is the former if the syllogism is not through immediate principles but through mediate ones. For in that case the first cause will not be employed, whereas science propter quid is according to the first cause; consequently, the former will not be science propter quid.Footnote 42

Epistemic faith, as I have presented it, relies on Thomas’ schema of subordinate sciences.Footnote 43 While the question of transmission is central to the ‘teacher testimony’ identified in Siebert’s study, Thomas’ treatment of ‘expert testimony’ in this context focuses on the distinction between a higher subordinating and a lower subordinated science, not testimony. Granted, Thomas does refer to the role of experts within scientific practice.Footnote 44 But he soon returns to the issue of ‘proximate principles’ within a science and no longer invokes experts or testimony to explain subordination.Footnote 45 At this point, then, one might draw the following distinction between epistemic and societal fides: societal fides is a form of testimony inasmuch as it consists in the transmission of truths between persons. Epistemic fides, by contrast, may include testimony but it is not necessarily or always, considered in itself, testimonial.Footnote 46 Epistemic fides concerns the acceptance of principles from ‘higher’ sciences. There are different modes of transmitting truths of a higher science, and these modes may or may not be inter-personal. Let us consider some examples:

Someone who is not a physicist may accept as true the principle that ‘for every action there is an equal and opposite reaction’. Though this is, of course, often called one of ‘Newton’s Laws’, it does not seem that the non-physicist accepts them qua testimony (i.e., because Isaac Newton or someone else asserted it as true) but, rather, as established truths within a given discipline (in this case, physics). Of course, the way in which this non-physicist might come to know them might be through the testimony of an expert, a peer, or teacher, but the conviction of these truths – the conviction allowed through non-theological faith – does not rest only or primarily on testimony. While someone might, in practice, depend on the testimony of an expert, subalternation for Thomas Aquinas is a classification of the relationship between higher and panolower sciences, not the assessment of individuals’ expertise or truthfulness. Though who is testifying might influence the conviction (or lack thereof) of the recipient of this testimony, it need not. So, continuing the example of the psychiatrist above, her certitude about the nature and efficacy of a given drug need not depend on the testimony of a chemist but instead on the established discoveries of the science of chemistry.Footnote 47 Thus, epistemic fides is not necessarily testimonial and should be distinguished from societal fides. It is important to note the possible testimonial independence of epistemic fides because of an underlying, distinct but related, controversy: whether subordinated sciences, testimony, both, or neither might yield genuine scientia.Footnote 48 Regarding both senses of non-theological faith as testimonial blurs key distinctions within this debate.

3. The importance of non-theological fides

Thus far, we have considered two non-theological senses of fides as formulated in the De Trinitate commentary: epistemic and societal. At this point, one might object to using the same term, fides, to refer to both theological and non-theological faith. If by ‘faith’ one means always and only religious faith, then the epistemic and societal senses identified in the present study are mistaken expansions of the term. To assert that fides is univocal in this way, though, begs the question of the present study by maintaining that this term refers always and only to theological faith. How, then, might one defend the proposed expansion of this term while avoiding equivocation? Throughout his presentations of fides, Thomas identifies the object of this virtue as truth. In the context of theological fides, this is the ‘First Truth’, God, and all other things inasmuch as they relate to God.Footnote 49 Insofar as both epistemic and societal fides concern truth (the truths of a given science or the truths asserted in society), they can also be termed fides without falling prey to equivocation. Thus, fides is an analogical term, whose various senses are united insofar as each relates, in one way or another, to truth.

While Thomas himself references these two non-theological senses of fides only in passing – and epistemic faith more than societal faith – investigation into his reasoning for both has revealed insights into his view of faith, scientific practice, and society. In neither epistemic nor societal faith does one rely on theology or revelation. Instead, both are natural instances of granting assent to a given proposition. Before ending this study, it is fitting to reflect on the importance of affirming these two non-theological senses of fides and then to consider what entrée they might offer to theological faith.

Epistemic faith allows one to accept the conclusions from one science and implement them as principles in another (such as a psychiatrist making use of chemistry). Without epistemic fides, subordinate sciences would either need to investigate demonstrations for their own principles or would need to be made unsubordinated and first. To do so, though, would undercut the very essence of a subordinate science which would, in turn, destroy the relation between sciences. Theoretically, a science providing demonstrations of its own principles makes itself susceptible to the problem that launched Aristotle’s Posterior Analytics: namely, that any discipline that demonstrates the principles of its certitude is trapped in an infinite regress. Practically, too, a denial of subordination would mean that there is no hierarchy or relation between sciences. If each science is made a first, then different areas of investigation would be siloed from another. But this is belied by common scientific practice in which the practitioner of one discipline implements or even depends on the findings of a different discipline.Footnote 50

One might, of course, try to maintain that in such ‘borrowings’, one changes disciplines, such that when a physicist is considering a mathematical formula she is then working as a mathematician, or when a theologian uses scripture to consider a moral issue she is then working as a moralist. Yet this suggestion seems odd. Would one wish to maintain, say, that a psychiatrist is no longer a psychiatrist but rather a chemist when he, for example, prescribes a ‘selective serotonin reuptake inhibitor’ (SSRI) to a patient because such medication functions as a chemical messenger? It seems not.Footnote 51 The specific discipline of psychiatry is different from but related to chemistry. The psychiatrist accepts the findings of chemistry as principles and applies them in his treatment.Footnote 52 In this way, the psychiatrist is practicing psychiatry as a subordinate discipline.

Turning to societal faith, this is central to Thomas’ view of human nature and society. The lack of belief in the words or actions of another, he maintains, makes a given society unable to function. This kind of faith, thus, makes possible the kind of communication needed for a society to exist. At this point, though, I should note a likely contrast between epistemic and societal fides. As we have seen, epistemic fides does not lose certitude insofar as it figures within Thomas’ notion of subordination. But, while epistemic fides relates to principles of a science, societal fides concerns human speech and activity, which can be highly dubitable. Nonetheless, Thomas insists that faith is indispensable for a society. Apparently aware of the difference between fides of this sort and the fides of principles (both natural and theological), Thomas does not claim certitude from societal fides. He does, however, insist that the violation of the trust manifested by fides is a seriously grave matter, such that lies are a direct attack upon the fides upon which a society depends for its survival.

4. Non-theological fides as entrée to theological faith?

The importance of fides in Thomas Aquinas’ thought seems rivaled only by its misperceptions. Religious ‘faith’ is, today, often presented as a subjective, non-critical, or dubitable attitude. Such characterizations are foreign to Thomistic accounts of faith. In his view, faith does not subvert or weaken rationality but, instead, perfects our natural ability to know. As he states,

it must be said that gifts of grace are added to those of nature in such a way that they do not destroy the latter, but rather perfect them; wherefore also the light of faith, which is gratuitously infused into our minds, does not destroy the natural light of cognition, which is in us by nature.Footnote 53

Thomas thus argues that, while theological faith accesses truths that are not naturally knowable (because they exceed human reason), it does not destroy natural knowledge. Indeed, there can be no contradiction between faith and natural knowledge because both arise, ultimately, from the same source.Footnote 54

This view of the fundamental harmony between reason and faith leads Thomas to argue that theology (sacra doctrina) may invoke natural reason to demonstrate certain preambles to faith, to clarify the meaning of certain revealed truths, or to refute those who deny these truths.Footnote 55 In defending his claim that natural knowledge might be incorporated within theological practice, Thomas contends that

When one of two things passes into the dominion of another, the product is not considered a mixture except when the nature of both is altered. Wherefore those who use philosophical doctrines in sacred Scripture in such a way as to subject them to the service of faith, do not mix water with wine, but change water into wine.Footnote 56

Thus, one sees that any suggestion that faith and reason are irreconcilable or radically separate is incompatible with the Thomistic account of fides. Nonetheless, the alleged separation of natural reason and religious belief remains all too common. One way of attempting to bridge this divide is to recognize natural or non-theological senses of faith and the indispensable roles of such faith within human life. Accepting truths through non-theological faith, both epistemically and socially, may even serve as entrées to theological faith inasmuch as they habituate us to acknowledging the mediated character of our knowledge.

Thomas himself suggests, albeit in passing, that ‘science begets and nourishes faith, by way of external persuasion afforded by science’.Footnote 57 This passage appears in the context of investigating the causes of faith when Thomas replies to an objection that there is no need for divine infusion of faith because, following Augustine, ‘science begets faith in us, and nourishes, defends and strengthens it’.Footnote 58 In his reply, Thomas insists that the ‘chief and proper cause’ of faith is an inward movement (i.e., the result of an infusion of grace), but this does not preclude or eliminate ‘external persuasions’. Examples of such ‘external’ inducements provided by Thomas include witnessing a miracle or being converted by the words of another.Footnote 59 He acknowledges that these are not sufficient in themselves to yield theological faith but nonetheless maintains that these external factors might lead to such faith.

In another passage Thomas argues that, while theological fides properly precedes other virtues (inasmuch as it directly concerns the end to which all other virtues are ordered), other virtues may, in practice, precede theological fides. Footnote 60 The examples he mentions are fortitude (which allows one to overcome the fear that might hinder faith) and humility (which allows the submission needed for faith). Might not the acknowledgment of epistemic and societal faith within human life also, in practice, precede and even serve as external inducements to theological faith? Recognizing the role of faith within scientific practice may allow one to bridge modern divides between science and theology because both rely on a kind of fides. Societal faith, too, allows one to recognize that human society itself depends on fides between its members. Though outliers of Thomas’ extended treatments of fides, acknowledging epistemic and societal fides might help to dispel mischaracterizations of faith as fundamentally unreasonable. In sum, inasmuch as these non-theological senses of fides allow one to overcome the perceived irreconcilability of faith and reason, they may serve as entrées to theological fides.

5. Conclusion

In the present study, I have explored two non-theological senses of faith in the thought of Thomas Aquinas: epistemic and societal fides. In drawing attention to these senses, I do not intend to downplay the importance of faith as a theological virtue. As mentioned in the beginning of this study, theological faith is, ultimately, the most important sense of fides and, consequently, rightfully occupies the majority of Thomas’ attention. Yet, as we have seen, non-theological faith is indispensable in human life and can challenge perceptions of faith as fundamentally unreasonable. Far from weakening the meaning and significance of theological faith, these non-theological senses can instead expand and enrich our understanding of fides, not only in the thought of Thomas Aquinas but also in our own lives.Footnote 61


1 An example of the tendency to focus on the theological meaning of fides can be found in Bruno Niederbacher’s, ‘The Relation of Reason to Faith’, in The Oxford Handbook of Aquinas, ed. by Brian Davies (Oxford: Oxford University Press, 2012), pp. 337–47. Though Niederbacher defends the ultimate compatibility of faith and reason, he begins by separating them. Richard Swinburne also offered an account of ‘The Thomistic View of Faith’ which focuses exclusively on its religious purpose in Faith and Reason (Oxford: Oxford University Press, 1999), pp. 138–41.

2 See Thomas Aquinas, Summa Theologicae I, q. 8. English translation from Fathers of the English Dominican Province (New York: Benziger Brothers, 1947). Henceforth, ST.

3 The various senses of fides have not gone entirely unnoticed. Deferrari, for instance, outlined five distinct senses of ‘faith’ as an act, a habit, an object, a characteristic, or a security. See Roy J. Deferrari, A Lexicon of St. Thomas Aquinas based on the Summa Theologica and Selected Passages of His Other Works (Washington: Catholic University of America Press, 1948), p. 419 ff. Thomistic scholarship in general, though, tends to investigate fides as a theological virtue more than these non-theological uses of the term.

4 For some treatments of this work, see Leo Elders, Faith and Science: An Introduction to St. Thomas’ Expositio in Boethii De Trinitate (Roma: Herder, 1974); Douglas C. Hall, The Trinity: An Analysis of St. Thomas Aquinas’ ‘Expositio’ of the ‘De Trinitate’ of Boethius (Leiden: E. J. Brill, 1992); Lawrence J. Donoho, ‘The Nature and Grace of Sacra Doctrina in St. Thomas’s Super Boethium De Trinitate’, The Thomist, 63 (1999), 343–401; Jean-Pierre Torrell, ‘Philosophie et théologie d’après le Prologue de Thomas d’Aquin au Super Boetium De Trinitate: Essais d’une lecture théologique’, Documenti e studi sulla Tradizione filosofica medievale, 10 (1999), 299–353; Matthew Kostelecky, ‘Thomas Aquinas’ Commentary on Boethius’ De Trinitate and the Structure of the Summa contra gentiles’, Religious Studies and Theology, 35 (2016), 145–62. See also Faustinus Ik. Ugwuanyi, ‘Why Aquinas Stopped Commenting on Boethius’s De Trinitate’, Studia Gilsoniana, 9 (2020), pp. 167–88. A study of this commentary which does not treat the function of fides but instead focuses on the role of question V for Thomistic epistemology is Ariberto Acerbi’s, ‘Aquinas’s Commentary on Boethius’s ‘De Trinitate’, The Review of Metaphysics, 66 (2012), 317–38.

5 As he explains, ‘we must understand what science should be called divine science. We must realize indeed that if a science considers a subject-genus, it must investigate the principles of that genus, since science is perfected only through knowledge of principles’. Thomas Aquinas, Super Boetium De Trinitate, q. 5 a. 4, c. (English translation: Armand Mauer, 1953.) Translation modified when noted.

6 Thomas Aquinas, Super Boetium De Trinitate, q. 2 a. 2, c.

7 Thomas Aquinas, Super Boetium De Trinitate, proemium. See also Super Boetium De Trinitate, q. 2 a. 2, c.

8 These first principles of theology are the articles of faith, as Thomas makes clear at Summa theologia I, q. 1, a. 8, c. Adverting to the earlier presentation of sacra doctrina, Thomas later explains in ST II-II, q. 1, a. 7 that the articles of faith ‘stand in the same relation to the doctrine of faith, as self-evident principles to a teaching based on natural reason’. These formulae of belief are necessary, Thomas maintains, because one ‘cannot believe, unless the truth be proposed to him that he may believe it. Hence the need for the truth of faith to be collected together, so that it might the more easily be proposed to all, lest anyone might stray from the truth through ignorance of the faith’. (ST II-II, q. 1, a. 9, c) Thomas offers an extensive commentary on these articles in his Expositio in Symbolum Apostolorum where Thomas delineates twelve propositions, each divinely revealed, that encapsulate the object of Christian belief. See also his short work De articulis Fidei et Ecclesiae sacramentis ad archiepiscopum Panormitanum. In this last work, Thomas presents a listing of the articles of faith that both cites the scriptural support with a given article and defends the article against various theological or philosophical criticisms.

9 Thomas Aquinas, Super Boetium De Trinitate, q. 2, a. 2, ad 5. (English translation of questions 1–4 by Rose E. Brennan, 1946.) Translation modified when noted.

10 Thomas Aquinas, Super Boetium De Trinitate q. 2, a. 2, ad 7.

11 Although Thomas references this non-theological sense of fides within scientific practice and the subordination of the sciences, referring to it as ‘scientific faith’ would be misleading if taken to refer to belief in science or even to religious belief mediated by science. Thomas’ understanding of ‘science’, too, is broader than the modern conception and encompasses any organized body of demonstrated knowledge (including, importantly, theology). I will, therefore, refer to this non-theological sense of faith as ‘epistemic’ rather than ‘scientific’ since it concerns knowledge broadly construed. I note that Jonathan Jenkins Ichikawa has used the term ‘epistemic faith’ in his treatment of ‘Faith and Epistemology’, Episteme, 17 (2020), 121–40. By ‘epistemic faith’ he means ‘an approximation, a reliance upon certain epistemic procedures, despite their apparent epistemic shortcomings. Faith is unjustified, and issues into unjustified beliefs, when the apparent epistemic shortcomings really do undermine reasonable belief; it is justified when the epistemic worries are insufficient or unfounded’ (p. 121). As will be clear in the body of my study, this is a very different usage from my employment of the term.

12 Thomas clearly has in mind the meaning of science as found in the Posterior Analytics, but now he is applying it to theology. As he states in the opening of his response: ‘the essence of science consists in this, that from things known a knowledge of things previously unknown is derived, and since this may occur in relation to divine truths, evidently there can be a science of divine things’. (Super Boetium De Trinitate, q. 2, a. 2, reply.).

13 Thomas Aquinas, Super Boetium De Trinitate, q. 2, a. 2, reply.

14 Thomas Aquinas, Super Boetium De Trinitate, q. 2, a. 2, ad 4.

15 Thomas Aquinas, Super Boetium De Trinitate, q. 2, a. 2, ad 5. (Translation modified).

16 Aristotle, Posterior Analytics I, 7, 7508b13-17. In the present study, I will use ‘subordinate’ and ‘subalternate’ interchangeably.

17 See Thomas Aquinas, Expositio libri Posteriorum Analyticorum I, lectio 25. For an extended treatment of subalternation in Thomas’ thought, see John I. Jenkins, Knowledge and Faith in Thomas Aquinas (Cambridge: Cambridge University Press, 1997), especially part I.

18 See Thomas Aquinas, Expositio libri Posteriorum Analyticorum I, lectio 25.

19 Thomas Aquinas, Super Boetium De Trinitate, q. 2, a. 2, ad 7 (translation modified).

20 At this point, I should note that in this example the psychiatrist is not depending on an individual chemist but on the chemical discoveries of this ‘higher’ science. The importance of this distinction will become clear in a later section of my study.

21 Of course, Thomas also maintains that theological faith is reasonable. For a study of this point, see Dominic Legge, ‘Reasonable Belief: The Contribution of Aquinas and his Dominican Followers on the Act of Faith and its Reasonableness’, Angelicum, 93 (2016), 315–30.

22 Thomas Aquinas, Super Boetium De Trinitate, q. 3, a. 1, response. (Translation modified).

23 Thomas Aquinas, Super Boetium De Trinitate, q. 3, a. 1, sed contra. I note at this point that Thomas also maintains that theological faith and, similarly, the discipline of theology itself are also necessary for human beings. The grounding for this claim is, of course, Thomas’ view of the ultimate end of human beings: namely, to obtain eternal life with God. To explore this sense of necessity, though critical for Thomas’ overarching theological project, is outside the scope of the present study inasmuch as it directly concerns theological fides.

24 Thomas Aquinas, Super Boetium De Trinitate, q. 3 a. 1, c.

25 Thomas Aquinas, ST II-II, q. 109, a. 3, ad 1.

26 Thomas Aquinas, ST II-II, q. 114, a. 2, ad 1.

27 Marie I. George has explored the connection between trust (a parallel to societal fides) and human nature in her ‘Aquinas on Trust and Our Social Nature’, The Renewal of Civilization: Essays in Honor of Jacques Maritain, ed. by Gavin Colvert (Washington, DC: American Maritain Association, 2010), pp. 110–25.

28 Of course, whom we believe is, ultimately, a matter of trustworthiness (those we believe to stand by their word, fulfill promises, testify truthfully, and so forth), while what we believe encompasses the various truths, values, or convictions that an individual, group, or society may accept. To explore the whom or the what of faith, though extremely important in themselves, lies outside the purview of the present study.

29 Mathew Kent Siebert, ‘Aquinas on Testimonial Justification: Faith and Opinion’, The Review of Metaphysics, 69 (2016), 555–82.

30 Siebert, 556.

31 Siebert, 560.

32 Siebert, 557–559.

33 Siebert, 560.

34 See, for instance, Siebert 557–560.

35 Thomas Aquinas, Super Boetium De Trinitate, q. 3, a. 1, sed contra.

36 Siebert, 560.

37 Siebert, 560.

38 See Thomas Aquinas, Expositio libri Posteriorum Analyticorum I, lectio 19.

39 Paul Faulkner, ‘The Social Character of Testimonial Knowledge’, Journal of Philosophy, 97 (2000), 581–601, p. 585. Jennifer Lackey makes a similar claim in her study, ‘It Takes Two to Tango: Beyond Reductionism and Non‐Reductionism in the Epistemology of Testimony’, The Epistemology of Testimony, ed. by J. Lackey and E. Sosa (Oxford: Oxford University Press, 2006), pp. 160–82, especially p. 176. See also Christopher R. Green, ‘Epistemology of Testimony’, Internet Encyclopedia of Philosophy (ISSN 2161-0002): ‘Discussing the basis of different beliefs presupposes that one important way we should categorize beliefs is by where they came from. The basis of a belief is its source or root. … when someone tells us that p, and we accept it, we form a testimonially-based belief that p. Testimony in this sense need not be formal testimony in a courtroom, but happens whenever one person tells something to someone else’. <> [accessed 24 November 2023].

40 For instance, Axel Gelfert states that: ‘In contemporary epistemology, “testimony” is most frequently used as an umbrella term to capture all those situations in which we form beliefs or acquire knowledge on the basis of what someone tells us. This includes spoken as well as written statements, media reports, corporate communications, scientific publications and the like’. Axel Gelfert, ‘Testimony’, in Routledge Encyclopedia of Philosophy (Taylor and Francis. DOI:10.4324/0123456789-P049-2. Accessed: 24 November 2023). Siebert does not offer a definition of ‘testimony’, but he seems to tacitly accept that testimony is inter-personal in some way.

41 See Thomas Aquinas, Expositio libri Posteriorum Analyticorum I, lectio 23.

42 See Thomas Aquinas, Expositio libri Posteriorum Analyticorum I, lectio 23.

43 Thomas Aquinas uses the terminology of propter quid when presenting the meaning of subalternation within his commentary at Super Boetium De Trinitate, q. 5, a. 1, ad 5.

44 Cf. Thomas Aquinas, Super Boetium De Trinitate, q. 2, a. 2, ad 7.

45 Thomas Aquinas, Super Boetium De Trinitate, question 2, a. 3, ad 7: ‘Sciences which are ordered to one another are so related that one can use the principles of another, just as posterior sciences can use the principles of prior sciences, whether they are superior or inferior: wherefore metaphysics, which is superior in dignity to all, uses truths that have been proved in other sciences. And in like manner theology – Although all other sciences are related to it in the order of generation, as serving it and as preambles to it – can make use of the principles of all the others, even if they are posterior to it in dignity’.

46 To turn to Thomas’ Expositio libri Posteriorum Analyticorum for a moment, there is reference within his treatment of subalternate sciences to experts in a ‘higher’ science and practitioners of a ‘lower’ one. Thomas only argues, though, that the former has propter quid knowledge and the latter has quia, not that the practitioner need necessarily depend on the individual expert for the principles needed within his own discipline. See Expositio libri Posteriorum Analyticorum I, lectio 25. Similarly, in the Super Boetium De Trinitate, q. 2, a. 3, ad 7, Thomas argues that ‘sacra doctrina utitur philosophicis documentis propter se, non recipit ea propter auctoritatem dicentium, sed propter rationem dictorum, unde quaedam bene dicta accipit et alia respuit’.

47 The issue of present concern is whether non-theological fides is reducible to testimony. I thus leave unanswered the question of how, apart from testimony, the insights of a ‘higher’ science might be transmitted to ‘lower’ sciences.

48 Siebert acknowledges the ‘the controversial question whether, on Aquinas’s account of knowledge, testimony can provide knowledge’ at 556, n. 5.

49 Cf. Thomas Aquinas, ST II-II, q. 1, a. 1.

50 In philosophical and theological practice, too, it is difficult if not impossible to separate, for example, politics from ethics or epistemology from anthropology or scripture from dogmatics and morals.

51 At the same time, a psychiatrist does not need the same kind of depth of knowledge of the chemical composition or nature of an SSRI as a chemist might. This is not, of course, to say that the chemical composition is irrelevant to a psychiatrist, but their concern in most instances is on the function of the compound, not the composition.

52 Thomas himself uses a medical example to explain how theology accepts principles on faith in Super Boetium De Trinitate, q. 2, a. 2, ad 5.

53 Thomas Aquinas, Super Boetium De Trinitate, q. 2, a. 3, reply.

54 See Thomas Aquinas, Super Boetium De Trinitate, q. 2, a. 3, reply.

55 See Thomas Aquinas, Super Boetium De Trinitate, q. 2, a. 3, reply.

56 Thomas Aquinas, Super Boetium De Trinitate, q. 2, a. 3, ad 5. (Translation modified).

57 Thomas Aquinas, ST II-II, q. 6, a. 1, ad 1.

58 Thomas Aquinas, ST II-II, q. 6, a. 1, obj. 1.

59 See Thomas Aquinas, ST II-II, q. 6, a. 1, reply.

60 Cf. Thomas Aquinas, ST II-II, q. 4, a. 7.

61 My thanks to the anonymous reviewer who offered insightful critiques of an earlier version of this study.