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Faith and Reason. The relation of faith to reason is of utmost importance for the thinking believer. The problem of how to combine these aspects of personhood has existed from the earliest apologists. Justin Martyr, Clement of Alexandria, and Tertullian all struggled. Augustine made the first serious attempt to relate the two, but the most comprehensive treatment came at the end of the medieval period when Christian intellectualism flowered in the work of Thomas Aquinas.
Relation of Faith to Reason. Aquinas held that faith and reason intertwine. Faith uses reason, and reason cannot succeed in finding truth without faith.
Reason Cannot Produce Faith. Reason accompanies, but does not cause, faith. Faith is consent without inquiry in that faith’s assent is not caused by investigation. Rather, it is produced by God. Commenting on Ephesians 2:8–9, Aquinas contended that “free will is inadequate for the act of faith since the contents of faith are above reason.… That a man should believe, therefore, cannot occur from himself unless God gives it” (Aquinas, Ephesians, 96; unless noted, all citations in this article are from works by Thomas Aquinas). Faith is a gift of God, and no one can believe without it.
Nonetheless, “this does not prevent the understanding of one who believes from having some discursive thought of comparison about those things which he believes” (On Truth, 14.A1.2). Such discursive thought, or reasoning from premises to conclusions, is not the cause of the assent of faith, but it can and should accompany it (ibid., 14.A1.6). Faith and reason are parallel. One does not cause the other because “faith involves will (freedom) and reason doesn’t coerce the will” (ibid.). A person is free to dissent, even though there may be convincing reasons to believe.
As a matter of tactical approach in apologetics, if the authority of Scripture is accepted (faith), appeal can be made to it (reason). “Thus, against the Jews we are able to argue by means of the Old Testament, while against heretics we are able to argue by means of the New Testament. But Mohammedans [see Islam] and the pagans accept neither the one nor the other.… We must, therefore, have recourse to the natural reason, to which all men are forced to give their assent” (Summa Theologica, 1a.2.2).
However, some Christian truths are attainable by human reason, for example, that God exists and is one. “Such truths about God have been proved demonstratively by the philosophers, guided by the light of the natural reason” (ibid., 1a.3.2)
Three Uses of Reason. Reason or philosophy can be used in three ways, Aquinas says:
- It demonstrates the “preambles of faith” (that God exists, that we are his creatures …; see Cosmological Argument; God, Evidence for).
- It analyzes teachings of philosophers in order to reveal corresponding concepts in Christian faith. Aquinas gives the example of Augustine’s On the Trinity, which draws on philosophy to help explain the Trinity.
- It opposes attacks against faith from logic (Gentiles, 1.9).
Reason can be used to prove natural theology, which studies the existence and nature of one God. It can be used to illustrate supernatural theological concepts, such as the Trinity and the Incarnation (see Christ, Deity of). And it can be used to refute false theologies (De Trinitate, 2.3). The apologist directs the person to accept two kinds of truth about divine things and to destroy what is contrary to truth. The person is directed to the truths of natural theology by the investigation of the reason and to the truths of supernatural theology by faith.
So to make the first kind of divine truth known, we must proceed through demonstrative arguments. However, since such arguments are not available for the second kind of divine truth, our intention should not be to convince our adversary by arguments: It should be to answer his arguments against the truth; for, as we have shown, the natural reason cannot be contrary to the truth of faith. The sole way to overcome an adversary of divine truth is from the authority of Scripture—an authority divinely confirmed by miracles. For that which is above the human reason we believe only because God has revealed it. Nevertheless, there are certainly likely [probable] arguments that should be brought forth in order to make divine truth known. [Gentiles, 1.9; see Miracles, Apologetic Value of]
God’s existence is self-evident absolutely (in itself) but not relatively (to us) (ibid., 1.10–11; see First Principles). Hence, in the final analysis, one must receive by faith those things that can be known by reason, as well as those things that lie above reason. Intellectual assent that lacks faith cannot have certitude, for human reason is notoriously suspect when it comes to spiritual matters. Consequently, “it was necessary for divine truth to be delivered by way of faith, being told to them as it were, by God Himself Who cannot lie” (Summa Theologica, 2a2ae.1, 5.4).
Divine Authority. Aquinas did not believe that reason provides the basis for believing in God. It can prove that God exists, but it cannot convince an unbeliever to believe in God.
Reason Prior to Faith. We may believe (assent without reservation) in something that is neither self-evident nor deduced from it by a movement of the will. However, this does not mean that reason plays no prior role to belief. We judge a revelation to be worthy of belief “on the basis of evident signs or something of the sort” (ibid., 2a2ae.1, 4. ad 2).
Reason inquires about what is to be believed before it believes in it. “Faith does not involve a search by natural reason to prove what is believed. But it does involve a form of inquiry unto things by which a person is led to belief, e.g. whether they are spoken by God and confirmed by miracles” (ibid., 2a2ae.2, 1, reply). Demons are not willingly convinced by the evidence that God exists but are intellectually forced by confirming signs to the fact that what the faithful believe is true. Yet they cannot truly be said to believe (On Truth, 14.9. ad 4).
The Testimony of the Spirit. In order to believe in God one must have the inner testimony of the Holy Spirit (see Holy Spirit, Role in Apologetics). For “one who believes does have a sufficient motive for believing, namely the authority of God’s teaching, confirmed by miracles, and—what is greater—the inner inspiration [instinctus] of God inviting him to believe” (Summa Theologica, 2a2ae.6.1). The Holy Spirit uses two causes to stimulate voluntary faith. The persuasion may be from without, for example, a miracle that is witnessed. Or persuasion may be from within. The first cause is never enough for one inwardly to assent to the things of faith. The assent of faith is caused by God as he moves the believer inwardly through grace. Belief is a matter of the will, but the will needs to be prepared by God “to be lifted up to what surpasses nature” (ibid., 2a2ae.2, 9. ad 3).
Reason in Support of Faith. Commenting on the use of reason in 1 Peter 3:15, Aquinas argued that “human reasoning in support of what we believe may stand in a two-fold relation to the will of the believer.” First, the unbeliever may not have the will to believe unless moved by human reason. Second, the person with a will ready to believe loves the truth, thinks it out, and takes to heart its evidence. The first, unbelieving will may come to a faith of sorts, but there will be no merit in it, because belief does not extend far beyond sight. The second person also studies the human reasoning, but it is a meritorious work of faith (ibid., 2a2ae.2, 10).
Positive Evidence. Faith is supported by, though not based on, probable evidence. “Those who place their faith in this truth, however, ‘for which the human reason offers no experimental evidence,’ do not believe foolishly, as though ‘following artificial fables’ ” (2 Peter 1:16). Rather, “It reveals its own presence, as well as the truth of its teaching and inspiration, by fitting arguments; and in order to confirm those truths that exceed natural knowledge, it gives visible manifestations to works that surpass the ability of all nature.” The kind of positive evidence that Aquinas used included such things as raising the dead, miracles, and the conversion of the pagan world to Christianity (On Truth, 14.A1).
Negative Evidence. The negative evidence encompasses arguments against false religions, including things like their fleshly appeal to carnal pleasures, their teachings that contradict their promises, their many fables and falsities, the lack of miracles to witness to divine inspiration of their holy book (like the Qur’an), use of warfare (arms) to spread their message, the fact that wise men did not believe Muhammad, only ignorant, desert wanderers, the fact that there were no prophets to witness to him, and Muslim perversions of Old and New Testament stories (Gentiles, 1.6).
Faith and Fallible Testimony. How can we be sure when the support of our faith rests on many intermediary (fallible) testimonies? Aquinas responds that the intermediaries are above suspicion if they were confirmed by miracles (for example, Mark 16:20). “We believe the successors of the apostles and prophets only in so far as they tell us those things which the apostles and prophets have left in their writings” (On Truth, 14.10, ad 11). The Bible alone is the final and infallible authority for our faith (see Bible, Evidence for).
Faith and Demonstrative Arguments. Aquinas distinguished between two kinds of rational arguments: demonstrative and persuasive. “Demonstrative, cogent, and intellectually convincing argument cannot lay hold of the truths of faith, though it may neutralize destructive criticism that would render faith untenable.” On the other hand, “persuasive reasoning drawn from probabilities … does not weaken the merit of faith, for it implies no attempt to convert faith into sight by resolving what is believed into evident first principles” (De Trinitate, 2.1, ad 5).
Distinguishing Faith and Reason. Though faith is not separated from reason, Aquinas does formally distinguish between them. He believed they are related, but the relationship does not coerce a person to believe.
Faith in Relation to Reason. Human reason does not force faith. If it did, then faith would not be a free act. What happens is that “the mind of the one believing settles upon the one side of a question not in virtue of his reason but in virtue of his will. Therefore assent is understood in the definition [of faith] as an act of the mind in so far as the mind is brought to its decision by the will” (ibid., 2a2ae. 2, 1, ad 3).
Faith is not unreasonable. Faith is reason with assent. For “to ponder with assent is, then, distinctive of the believer: this is how his act of belief is set off from all other acts of the mind concerned with the true and the false” (Summa Theologica, 2a2ae.2, 1, reply). Faith, then, is defined as “that habit of mind whereby eternal life begins in us and which brings the mind to assent to things that appear not.” Faith differs from science in that the object of faith is unseen. It also differs from doubt, suspicion and opinion in that there is evidence to support faith.
Faith is a free act. Aquinas quotes Augustine with approval that “Faith is a virtue by which things not seen are believed” (ibid., 2a2ae.4, 1, reply). He declares that to believe is an act of mind assenting to the divine truth by virtue of the command of the will as this is moved by God through grace; in this the act stands under control of free will and is directed toward God. The act of faith is, therefore, meritorious. That is, one is rewarded for believing in what he does not see. There is no merit (reward) in believing what can be seen, since there is no faith involved; it can be seen. The scientist [i.e., philosopher] is impelled to assent by force of a conclusive proof. Thus the assent is not meritorious. [ibid., 2a2ae. 2, 9]
Faith is an act of mind and will. Since belief is an act of the intellect under the impetus of the will, it issues from both mind and will, and both are perfectible by action. “If an act of faith is to be completely good, then, habits must necessarily be present in both mind and will” (ibid., 2a2ae. 4, 2, reply). That is, one cannot be saved without a willingness to do something with faith. Saving faith will produce good works.
Meritorious Nature of Faith. Faith is meritorious, not because one has to work for it, but because it involves the will to believe. It “depends on the will according to its very nature (ibid., ad 5). “For in science and opinion [probable arguments] there is no inclination because of the will, but only because of reason” (ibid., 14.3, reply). But “no act can be meritorious unless it is voluntary, as has been said” (ibid., 14.5, reply).
Aquinas believed that Hebrews 11:1 is a good definition of faith, for it describes not merely what faith does but what it is. He saw in it the three essentials:
- It mentions the will and the object that moves the will as principles on which the nature of faith is based.
- In it we can distinguish faith from those things which appear not, as opposed to science and understanding.
- The whole definition reduces to the essential phrase, “the substance of things hoped for.” (ibid., 14.2)
The formal difference between faith and reason is that one cannot both know and believe the same thing at the same time. For “Whatever things we know with scientific knowledge properly so called we know by reducing them to first principles which are naturally present to the understanding.”
Faith and Knowledge about the Same Object. Scientific knowledge culminates in sight of the thing believed, so there is no room for faith. One cannot have faith and scientific knowledge about the same thing (ibid., 14.9, reply). The object of true faith is above senses and understanding. “Consequently, the object of faith is that which is absent from our understanding.” As Augustine said, “we believe that which is absent, but we see that which is present” (ibid., 14.9, reply).
This does not mean, of course, that everyone will necessarily believe what I can see without faith (Summa Theologica, 2a2ae.1, 5). It does mean that the same person cannot have both faith and proof of the same object. One who sees it, does not believe it by faith on the testimony of others. One who believes it on the testimony of another does not see (know) it personally.
Probable Knowledge and Faith. Likewise, one cannot have “opinion” (probable knowledge) and “science” (certain knowledge) about the same object. As Aquinas notes, “opinion includes a fear that the other part [of the contradiction] is true, and scientific knowledge excludes such fear. However, this fear that the opposite may be true does not apply to matters of faith. For faith brings with it a greater certitude than what can be known by reason” (On Truth, 14.9, ad 6).
Creedal Knowledge and Faith. If the existence of God can be proved by reason, and if what is known by reason cannot also be a matter of faith, then why is belief in God proposed in the Creed? Aquinas responds that not all are capable of demonstrating God’s existence. “We do not say that the proposition, God is one, in so far as it is proved by demonstration, is an article of faith, but something presupposed before the articles. For the knowledge of faith presupposes natural knowledge, just as grace presupposes nature” (ibid., 14.9, ad 8).
Perfected by Love, Produced by Grace. Reason can go only so far. Faith goes beyond reason and completes it. “Faith does not destroy reason, but goes beyond it and perfects it” (ibid., 14.10, reply, ad 7). “Love is the perfection of faith. Since charity is a perfection of the will, faith is formed by charity” (ibid., ad 1). “It is called form in so far as faith acquires some perfection from charity” (ibid., ad 7). But “the act of faith which precedes charity is an imperfect act awaiting completion from charity” (ibid., 14.A5, reply). So love perfects faith. Since believing depends on the understanding and the will, “such an act cannot be perfect unless the will is made perfect by charity and the understanding by faith. Thus formless faith cannot be a virtue” (ibid., ad 1).
However, “that which faith receives from charity is accidental to faith in its natural constitution, but essential to it with reference to its morality” (ibid., 14.6, reply).
Not only is love necessary to perfect faith, but grace is necessary to produce it. “Now, grace is the first [that is, remote] perfection of the virtues, but charity is their proximate perfection” (ibid., 14.A5, ad 6).
The Limitations of Reason. Aquinas did not believe that human reason was without limitations. In fact he offered many arguments as to why reason is insufficient and revelation is needed.
Five Reasons for Revelation. Following Jewish philosopher Moses Maimonides, Aquinas set forth five reasons why we must first believe what we may later be able to provide good evidence for (Maimonides, 1.34):
- The object of spiritual understanding is deep and subtle, far removed from sense perception.
- Human understanding is weak as it fights through these issues.
- A number of things are needed for conclusive spiritual proof. It takes time to discern them.
- Some people are disinclined to rigorous philosophical investigation.
- It is necessary to engage in other occupations besides philosophy and science to provide the necessities of life (On Truth, 14.10, reply).
Aquinas said it is clear that, “if it were necessary to use a strict demonstration as the only way to reach a knowledge of the things which we must know about God, very few could ever construct such a demonstration and even these could do it only after a long time.” Elsewhere, Aquinas lists only three basic reasons divine revelation is needed.
- Few possess the knowledge of God, some do not have the disposition for philosophical study, and others do not have the time or are indolent.
- Time is required to find the truth. This truth is very profound, and there are many things that must be presupposed. During youth the soul is distracted by “the various movements of the passions.”
- It is difficult to sort out what is false in the intellect. Our judgment is weak in sorting true from false concepts. Even in demonstrated propositions there is a mingling of false.
“That is why it was necessary that the unshakable certitude and pure truth concerning divine things should be presented to men by way of faith” (Gentiles, 1.4, 2–5).
The Noetic Effects of Sin. Clearly, the mind falls far short when it comes to the things of God. As examples of weakness Aquinas looked at the philosophers and their errors and contradictions. “To the end, therefore, that a knowledge of God, undoubted and secure, might be present among men, it was necessary that divine things be taught by way of faith, spoken as it were by the Word of God who cannot lie” (ibid., 2a2ae. 2, 4). For “the searching of natural reason does not fill mankind’s need to know even those divine realities which reason could prove” (ibid., 2a2ae.2, 4, reply).
As a result of the noetic effects of sin, grace is needed. Aquinas concluded that “If for something to be in our power means that we can do it without the help of grace, then we are bound to many things that are not within our power without healing grace—for example to love God or neighbor.” The same is true of belief. But with the help of grace we do have this power (ibid., 2a2ae.2, 6, ad 1).
However, Aquinas did not believe that sin destroyed human rational ability. “Sin cannot destroy man’s rationality altogether, for then he would no longer be capable of sin” (ibid., 1a2ae.85, 2).
Things above Reason. Not only is faith necessary because of human depravity, but also because some things simply go beyond the power of reason. That does not mean they are contrary to reason, but that they are not fully comprehensible. “Faith, however, is said to surpass reason, not because there is no act of reason in faith, but because reasoning about faith cannot lead to the sight of those things which are matters of faith” (ibid., 14.A2, ad 9). If one could base faith fully on reason, faith would not be a free act; it would be consent caused by the mind.
At two levels a matter of faith may be “above reason.” At its highest level it can be above reason absolutely—if it exceeds the intellectual capacity of the human mind (e.g., the Trinity). It is impossible to have scientific knowledge of this. Believers assent to it only on the testimony of God.” Or, it may not absolutely exceed the intellect capacity of all, but is exceedingly difficult to comprehend, and is above the intellectual capacity of some (for example, that God exists without body). “These we may have scientific proofs of and, if not, we may believe them” (On Truth, 14.9, reply).
We must have faith when the light of grace is stronger than the light of nature. For “although the divinely infused light is more powerful than natural light, in our present state we do not share it perfectly, but imperfectly.” Therefore, “because of this defective participation, through that infused light itself we are not brought to the vision of those things for the knowledge of which it was given us. But we will have it in heaven when we share that light perfectly and in the light of God we will see light” (Gentiles, 14.8, ad 2).
Faith, then, surpasses reason. For “some truths about God exceed all the ability of the human reason. Such is the truth that God is triune” (ibid., 1.3). The ineffable essence of God cannot be known by human reason. The reason for this is that the mind depends on the senses. “Now, sensible things cannot lead the human intellect to the point of seeing in them the nature of the divine substance; for sensible things are effects that fall short of the power of their cause” (ibid., 1.3, 3).
Just because we have no reasons for things that go beyond reason does not mean they are not rational. Every belief that is not self-evident can be defended as necessary. We may not know the argument, but it exists. It at least is known to God “and to the blessed who have vision and not faith about these things” (De Trinitate, 1.1.4; On Truth, 14.9, ad 1). While human reason cannot attain to the things of faith, it is the preface to them. While “philosophical truths cannot be opposed to truths of faith, they fall short indeed, yet they also admit common analogies; and some moreover are foreshadowing, for nature is the preface of grace” (De Trinitate, 2.3).
“Although the truth of the Christian faith which we have discussed surpasses the capacity of the reason, nevertheless that truth that the human reason is naturally endowed to know cannot be opposed to the truth of the Christian faith” (Gentiles, 1.7, ).
Summary. Aquinas’s view of the relation of faith and reason blends positive elements of presuppositionalism and evidentialism, of rationalism (see Descartes, Rene; Leibniz, Gottfried) and fideism. Aquinas stresses the need for reason before, during, and after beliefs are acquired. Even the mysteries of faith are not irrational.
On the other hand, Aquinas does not believe that reason alone can bring anyone to faith. Salvation is accomplished only by the grace of God. Faith can never be based on reason. At best it can only be supported by reason. Thus, reason and evidence never coerce faith. There is always room for unbelievers not to believe in God, even though a believer can construct a valid proof that God exists. Reason can be used to demonstrate that God exists, but it can never in itself persuade someone to believe in God. Only God can do this, working in and through their free choice.
These distinctions of Aquinas are eminently relevant to the discussion between rationalists and fideists or between evidentialists and presuppositionalists. With regard to belief that God exists, Aquinas sides with the rationalists and evidentialists. But with respect to belief in God, he agrees with fideists (see Fideism) and presuppositionalists (see Apologetics, Presuppositional).
- Norman L. Geisler, “Faith and Reason,” Baker Encyclopedia of Christian Apologetics, Baker Reference Library (Grand Rapids, MI: Baker Books, 1999)
- Norman L. Geisler, Thomas Aquinas: An Evangelical Appraisal
- M. Maimonides, A Guide for the Perplexed
- Thomas Aquinas, In Boethius, De Trinitate
- ———, Commentary on Saint Paul’s Epistle to the Ephesians
- ———, Summa Contra Gentiles
- ———, Summa Theologica
- ———, On Truth