Mark Twain once said, “Faith is believing what you know ain’t so”. This is almost certainly meant as a joke. But, behind the joke, there is a sincere and serious twofold critique of religious belief. First, there is the underlying suggestion that faith is, by its very nature, irrational: to believe something by faith is to believe against all evidence to the contrary. Second, there is the underlying suggestion that religious believers, deep down, know that their beliefs are irrational – and believe anyway. Twain, then, is accusing religious believers of not only believing things that are false, but of believing things that they know are false, and thus behaving irrationally. Twain’s take on religious belief is not an uncommon one. Many people think of the relationship between faith and reason as one of irresolvable conflict: those who believe by faith reject reason, and those who are reasonable reject faith. But are faith and reason really incompatible in this way? Is reason the only way of coming to know that something is true, or can we also learn things by means of faith? Could faith and reason somehow work together or complement one another? Can faith be reasonable?
Thomas Aquinas (1225-1274) was an Italian Dominican priest, philosopher, theologian, saint, and doctor of the Roman Catholic Church, famous for synthesizing the thought of Aristotle and Christian doctrine. His most important and well-known work is his Summa Theologiae (“Theological Summary” or “Summary of Theology”). Meant as an introduction to the study of theology, the Summa Theologiae is actually a massive work, covering a wide range of philosophical and theological topics, such as the existence and nature of God, the nature of human persons, the foundations of ethics, various virtues and vices, and the sacraments.
Here, we will be reading from Aquinas’s other summa, the Summa Contra Gentiles. This work was written as a handbook for preachers and missionaries to help them better articulate and defend the Christian faith to unbelievers. Like the Summa Theologiae, the Summa Contra Gentiles covers a wide range of philosophical and theological topics. Here, we will be taking a look at some of the early chapters of Book I in which Aquinas discusses the relationship between faith and reason. This material serves as a sort of prelude to the long and detailed discussions concerning the existence and nature of God that follow. The full text of the Summa Contra Gentiles can be found here.
Faith – The act of accepting a proposition as true for which there is less than demonstrable evidence, which rises above mere opinion but falls short of logical or scientific demonstration. Faith can also refer to a particular religious tradition or the body of beliefs that are central to that religious tradition.
Revelation – Theological truths that have been made known by means of some religious text, testimony, authority, or experience, or the act or process in which such truths are made known.
Fideism – The view that the only reliable means of coming to know truths about God is faith. As a result, what we might otherwise believe by means of reason ought to be disregarded or even rejected in favor of what we must believe by means of faith.
Rationalism – The view that the only reliable means of coming to know truths about God is reason. As a result, what we might otherwise believe by means of faith ought to be disregarded or even rejected in favor of what we must believe by means of reason.
Aquinas begins his discussion of the relationship between faith and reason by distinguishing between two types of truths about God: truths that surpass the capability of reason and so are strictly a matter of faith, and truths that do not surpass the capability of reason, and so can be known either by reason or by faith. Right off the bat, then, Aquinas signals his rejection of both fideism and rationalism in favor of a more moderate and complementary understanding of the relationship between faith and reason.
Book I, Chapter 3.2:
Now, in those things which we hold about God there is truth in two ways. For certain things that are true about God wholly surpass the capability of human reason: for instance, that God is triune. But there are certain things to which even natural reason can attain, for instance, that God exists, that God is one, and others like these, which even the philosophers, being guided by the light of natural reason, proved demonstratively about God.
According to Aquinas, there are certain truths about God which can be known by reason and others which can only be known by faith. Aquinas is short on examples here, but some of the examples he provides are that God exists, that there is only one God, that in God there are three persons, and that God became human for our salvation. Aquinas holds that the first two of these are truths that can be known by reason, whereas the last two can only be known by faith. But what do you think? How far can reason take us? Can it demonstrate the truth of all of these claims? Some of them? None of them? Where would you place reason’s edge? Come back to this question after you have read the rest of the article. Did you change your mind?
But why should we think that there are truths about God that exceed human reason? Why not think that the only truths that can be known about God are those that we can know by means of our natural capacities, that is, by means of reason and observation? Aquinas gives two main reasons for why we should expect there to be such truths:
Book I, Chapter 3.3, 3.5:
That certain divine truths wholly surpass the capability of human reason is most clearly evident.
For, since the principle of all the knowledge which reason acquires about a thing is the understanding of that thing’s essence…it follows that our knowledge about a thing will be in proportion to our understanding of its essence. Therefore, if the human intellect comprehends the essence of a particular thing, such as a stone or a triangle, no truth about that thing will surpass the capability of human reason. But this does not happen to us in relation to God, because the human intellect is incapable by its natural power of attaining to the comprehension of His essence. For our intellect’s knowledge, according to the mode of the present life, originates from the senses: and thus things which are not objects of sense cannot be comprehended by the human intellect except insofar as knowledge of them is gathered from sensible things. Now sensible things cannot lead our intellect to see in them what God is, because they are effects unequal to the power of their cause. And yet our intellect is led by sensible things to the divine knowledge so as to know about God that He is, and other such truths which need to be ascribed to the first principle. Accordingly, some divine truths are attainable by human reason, while others altogether surpass the power of human reason…
Furthermore, the same is made abundantly clear by the deficiency which we experience every day in our knowledge of things. For we are ignorant of many of the properties of sensible things, and in many cases we are unable to discover the nature of those properties which we perceive by our senses. Much less, therefore, is human reason capable of investigating all the truths about that most sublime essence.
According to the first argument, since our limited human intellects are incapable of grasping the full reality of God, we should expect that there are truths about God which we are simply incapable of understanding on our own. Why think that our limited human intellects are incapable of grasping the full reality of God? As Aquinas explains, we human beings rely on our senses to learn about the world around us. We look to the observable qualities of a thing to learn more about what that thing is. This is what Aquinas means by the “essence” of a thing. To understand the essence of a thing is to understand what kind of thing it is, what it is in itself.
But God is immaterial, and so does not have any observable qualities. The best we can do is observe His effects, the various ways in which He interacts with the material world. Those effects can reveal to us that God exists, and something about the sort of thing that He is, but we shouldn’t expect that they will tell us the whole story. The second argument is a bit more straightforward. Our limited human intellects seem hardly capable of grasping the full reality of the physical world (just think about all of the deep mysteries about our universe that continue to elude our grasp). So why should we think that they would be up to the task of fully grasping something outside of it?
For Aquinas, faith is not only an act but a virtue, that is, a disposition to act. More specifically, faith is a theological virtue. Theological virtues are those virtues by which we are directed toward God, which are directly infused in us by God through grace, and which prepare us for ultimate happiness with God in heaven in the life to come. Earlier we said that to believe something by faith or by means of faith or as a matter of faith is to accept some proposition as true in the absence of demonstrable evidence. For Aquinas, while this is a suitable definition for faith in general, in the case of truths about God there is a bit more to the story. To accept some proposition about God as true in the absence of demonstrable evidence requires the relevant infused virtue. One must have received the virtue of faith from God through grace in order to be able to come to believe the relevant proposition in that way. For more on faith as a theological virtue, see the relevant questions and articles of Aquinas’s Summa Theologiae, found here.
But why would God reveal certain truths about Himself which human beings are perfectly capable of discovering on their own by means of reason? Isn’t that unnecessary or redundant? Aquinas offers three reasons God might have for doing this:
Book I, Chapter 4.1-4.5:
While, then, the truth of the intelligible things of God is twofold—one to which the inquiry of reason can attain, the other which surpasses the whole range of human reason—both are fittingly proposed by God to man as an object of belief.
We must first show this with regard to that truth which is attainable by the inquiry of reason, lest it appear to some that, since it can be attained by reason, it is useless to make it an object of faith by supernatural inspiration. Now, there would be three unsuitable consequences if this truth were left solely to the inquiry of reason.
One is that few men would have knowledge of God. For very many are hindered from gathering the fruit of diligent inquiry, which is the discovery of truth, for three reasons.
Some, indeed, on account of an indisposition of temperament, from which many are naturally indisposed to knowledge, so that no efforts of theirs would enable them to reach to the attainment of the highest degree of human knowledge, which consists in knowing God. Some are hindered by the needs of household affairs. For there must be among men some that devote themselves to the conduct of temporal affairs, who would be unable to devote so much time to the leisure of contemplative research as to reach the summit of human inquiry, namely, the knowledge of God. And some are hindered by laziness. For in order to acquire the knowledge of God in those things which reason is able to investigate, one must have a previous knowledge of many things. For almost the entire consideration of philosophy is directed to the knowledge of God, on account of which metaphysics, which is about divine things, is the last of the parts of philosophy to be studied. Thus, it is not possible to arrive at the inquiry about the aforesaid truth except after a most laborious study, and few are willing to take upon themselves this labor out of the love of knowledge, even though God has instilled natural desire for it in the minds of men.
The second inconvenience is that those who would arrive at the discovery of the aforesaid truth would scarcely succeed in doing so after a long time. First, because this truth is so profound that the human intellect is only enabled to grasp it by reason after long practice. Second, because many things are required beforehand, as stated above. Third, because the mind is not fit for the knowledge of so sublime a truth at the time of youth, when tossed about by the various movements of the passions… Hence, mankind would remain in the deepest darkness of ignorance if the path of reason were the only available way to the knowledge of God, because the knowledge of God, which especially makes men perfect and good, would be acquired only by the few, and by these only after a long time.
The third inconvenience is that much falsehood is mingled with the investigations of human reason, on account of our intellect’s weakness in forming judgments, and the admixture of phantasms. Consequently, many would remain in doubt about those things even which are most truly demonstrated while ignoring the force of the demonstration, especially when they perceive that different things are taught by the various men who are called wise. Moreover, among the many demonstrated truths there is sometimes a mixture of falsehood, which is not demonstrated but asserted for some probable or sophistical reason which at times is mistaken for a demonstration. Therefore, it was necessary that definite certainty and pure truth about divine things should be offered to man by the way of faith.
Therefore, the divine mercy helpfully provides that even some things which reason is able to investigate are held by faith, so that all may share in the knowledge of God easily, and without doubt or error.
According to Aquinas, if God did not also reveal those truths that human beings are capable of discovering by means of natural reason, three “unsuitable consequences” or “inconveniences” would follow: few would know these truths about God, those few would only know these truths after a long period of study, and, even after having come to know such truths, those few would still retain some degree of doubt about them. God would reveal even those truths about Himself that are knowable by means of reason, then, to ensure that everyone, immediately, and with certainty, could come to know these truths.
Faith is sometimes defined as believing without evidence. While Aquinas does hold that what is believed by means of faith is believed in the absence of logical or scientific demonstration, he does not hold that what is believed by means of faith is believed in the absence of any evidence whatsoever. For Aquinas, the evidence for those truths believed by faith is revelation in its many forms (Scripture, testimony, religious authority, and religious experience) and what serves as confirmation of this evidence are miracles (healings, astronomical signs, supernatural gifts and abilities, and unexpected conversions):
Book I, Chapter 6.1-6.3:
Now those who believe this truth, of which reason affords no proof, believe not lightly, as though following foolish fables (2 Pet 1:16).
For divine wisdom himself, who knows all things most fully, deigned to reveal to man the secrets of God’s wisdom (Job 11:6), and by suitable arguments proves His presence, and the truth of His doctrine and inspiration, by performing works surpassing the capability of the whole of nature, namely, the wondrous healing of the sick, the raising of the dead to life, a marvelous control over the heavenly bodies, and, what excites yet more wonder, the inspiration of human minds, so that unlettered and simple persons are filled with the Holy Spirit, and in one instant are endowed with the most sublime wisdom and eloquence.
And after considering these arguments, convinced by the strength of the proof, and not by the force of arms, nor by the promise of delights, but—and this is the greatest marvel of all—amidst the tyranny of persecutions, a countless crowd of not only simple but also of the wisest men, embraced the Christian faith, which inculcates things surpassing all human understanding, curbs the pleasures of the flesh, and teaches contempt of all worldly things. That the minds of mortal beings should assent to such things is both the greatest of miracles, and the evident work of divine inspiration, seeing that they despise visible things and desire only those that are invisible.
And that this happened not suddenly nor by chance, but by the disposition of God, is shown by the fact that God foretold that he would do so by the manifold oracles of the prophets, whose books we hold in veneration as bearing witness to our faith…
Now, such a wondrous conversion of the world to the Christian faith is a most indubitable proof that such signs did take place, so that there is no need to repeat them when they are so evidently apparent from their effect. For it would be the most wondrous sign of all if, without any wondrous signs, the world were persuaded by simple and lowly men to believe things so arduous, to accomplish things so difficult, and to hope for things so sublime. Even now, in our time, God does not cease to work miracles through his saints in confirmation of the faith.
Aquinas thinks that it is reasonable to believe certain truths about God by faith. Here we should let revelation be our guide. For Aquinas, it is reasonable to believe certain truths that have been revealed about God even when we cannot reason our way to them. But there are many different faiths, and many different religious traditions, each one proposing different truths about God to be believed and different sources of revelation to serve as our guide. So how do we figure which faith to believe, which source of revelation to accept as a reliable source of truths about God?
Aquinas offers us two strategies for dealing with this problem, sometimes called The Problem of Religious Diversity. First, given that the truths of faith and the truths of reason cannot contradict one another (more on this later), we can evaluate the claims of certain religions based on how well they fit with what we already know by reason. If the claims of some particular religion conflict with what we already know by reason, then that is a reason to doubt those claims. However, Aquinas also thinks that humans are capable of faulty reasoning, so we have to be on guard for that possibility as well. Second, Aquinas thinks that the greatest confirmation that we can have for some particular revealed truth is that there are miraculous occurrences that validate it. For example, if practitioners of a particular religion have demonstrated an ability to perform supernatural feats, or if miraculous events have occurred in the context of a particular religion’s history or practice, then that is a reason to take seriously the possibility that that religion could be a potential source of revealed truth about God. However, Aquinas also thinks that human history contains plenty of examples of frauds and fakes, individuals who claim to have performed or witnessed miracles but were later debunked. And so we must always be on guard for that possibility as well.
According to Aquinas, then, there are two modes of truth, or two ways of coming to know truths about God: by reason and by faith through revelation. As we have seen, Aquinas thinks that there are good reasons to expect that there would be truths of both sorts. But how are these two modes of truth, two ways of coming to know truths about God, related to one another? Could truths from these two modes of knowing ever conflict? Here’s what Aquinas says:
Book I, Chapter 7.1, 7.2, 7.7:
Now, though the aforesaid truth of the Christian faith surpasses the ability of human reason, nevertheless those things which are naturally instilled in human reason cannot be opposed to this truth.
For it is clear that those things which are implanted in reason by nature are most true, so much so that it is impossible to think them to be false. Nor is it lawful to deem false that which is held by faith, since it is so evidently confirmed by God. Seeing, then, that the false alone is opposed to the true (as is obvious if we examine their definitions), it is impossible for the aforesaid truth of faith to be contrary to those principles which reason knows naturally.
Moreover, the same thing which the disciple’s mind receives from its teacher is contained in the knowledge of the teacher—unless he teach fictitiously, which is wicked to say of God. Now, the knowledge of naturally known principles is instilled into us by God, since God himself is the author of our nature. Therefore, the divine wisdom also contains these principles. Consequently, whatever is contrary to these principles is contrary to the divine wisdom. Therefore, it cannot be from God. Therefore, those things which are received by faith from divine revelation cannot be contrary to our natural knowledge.
From this we may evidently conclude that whatever arguments are alleged against the teachings of faith, they do not rightly proceed from the first self-evident principles instilled by nature. Hence, they lack the force of demonstration, and are either probable or sophistical arguments, and consequently it is possible to solve them.
In these passages, Aquinas says that, as a matter of principle, there could never be any real conflict between truths known through reason and truths known through faith by means of revelation. Any apparent conflict between the two is just that: an apparent conflict. In any apparent conflict, there must be some fault in our reasoning or in our interpretation of revelation (or both!).
In this passage Aquinas provides an argument for the conclusion that faith and reason can never really contradict one another. His argument appears to be this:
Premise 1: The faculties and principles by which we determine the truths of reason have been implanted in us by God, and so the truths of reason have as their ultimate source, God Himself.
Premise 2: The faculties and principles by which we come to accept the truths of faith have been revealed to us by God, and so have as their ultimate source, God Himself.
Premise 3: Hence, for the truths of faith and the truths of reason to contradict one another would be for God to contradict Himself.
Premise 4: But God cannot contradict Himself.
Premise 5: Therefore, the truths of faith and the truths of reason cannot contradict one another.
A key claim in this argument is premise 4. The main reason why the truths of faith and the truths of reason cannot contradict one another is that they have the same source: God Himself. Now, in other contexts, it is not impossible that two claims coming from the same source might contradict one another. After all, I can certainly contradict myself! But in the special case of God, Aquinas thinks that this is impossible. For, God is perfectly rational, and so cannot make a mistake, and God is perfectly good, and so cannot deceive us. We might still wonder whether the “truths” that we come to believe by either reason or revelation might actually be the result of confusion or distortion on our part, despite ultimately deriving from a reliable source. But, excepting that sort of case, Aquinas thinks what we should be able to trust both sources, and thus we should have confidence that they will ultimately produce the very same or complementary results.
In defending the compatibility of faith and reason, Aquinas upholds the reliability of both sources of knowledge. In this way he, once again, rejects both fideism and rationalism. According to Aquinas, faith through revelation is the most reliable and most certain source of knowledge about God, but reason also has a crucial role to play:
Book I, Chapter 9.1-9.2:
Accordingly, from what we have been saying, it is evident that the intention of the wise man must be directed to the twofold truth of divine things and to the refutation of contrary errors, and that reason’s investigation can reach one of these, but the other surpasses every effort of reason. And I speak of a twofold truth of divine things not on the part of God himself, Who is truth one and simple, but on the part of our knowledge, which has a variable relation to the knowledge of divine things.
Therefore, in order to deduce the first kind of truth, we must proceed by demonstrative arguments by which we can convince our adversaries. But, since there are no such arguments in support of the second kind of truth, our intention must be not to convince our opponent by our arguments, but to solve the arguments which he brings against the truth, because, as shown above, natural reason cannot be opposed to the truth of faith.
In a special way, the opponent of this kind of truth may be convinced by the authority of Scripture confirmed by God with miracles, since we do not believe what is above human reason unless God has revealed it.
In support, however, of this kind of truth, certain probable arguments must be adduced for the practice and help of the faithful, but not for the conviction of our opponents, because the very insufficiency of these arguments would rather confirm them in their error if they thought that we assented to the truth of faith on account of such weak reasonings.
According to Aquinas, reason can be used to demonstrate certain truths about God, it can be used to disarm or rebut objections raised against the truths of faith, and it can be used to provide arguments that show the truths of faith to be “likely” or “fitting”. As Aquinas explains, these latter arguments are not meant to convince anyone who is not already convinced of the relevant truths and so should not be used for that purpose. Rather, they are for the sake of the faithful in helping them to better understand what it is they already believe.
According to Thomas Aquinas, there are two ways of coming to know truths about God: by reason and by faith through revelation. Aquinas thinks that both reason and faith are reliable and authoritative. Moreover, he thinks that there are good reasons to expect that there would be truths of both sorts. And, finally, he thinks that, as a matter of principle, the truths of one can never really contradict the truths of the other.
For an explanation of Aquinas’s views from Fr. Dominic Legge, a Dominican priest, check out the following video:
To learn more about those truths about God that Aquinas thinks can be demonstrated by means of reason (such as that God exists, that there is only one God, and that God is perfectly good), keep reading Book I of the Summa Contra Gentiles, or check out similar discussions in his Summa Theologiae. You can also click here for the Philosophy Teaching Library entry on Aquinas’s famous Five Ways. To learn more about The Problem of Religious Pluralism, check out this online encyclopedia article on the topic.
This work has been adapted from Summa Contra Gentiles by Thomas Aquinas, translated by Fr. Laurence Shapcote, and made available online by the Aquinas Institute. This work is in the Public Domain. All images were created using Midjourney and are the property of the Philosophy Teaching Library.
Skryzypek, Jeremy. 2024. “Is Faith Irrational? Thomas Aquinas’s Summa Contra Gentiles, Book I, Chapters 3-9.” The Philosophy Teaching Library. Edited by Robert Weston Siscoe, <https://philolibrary.crc.nd.edu/article/is-faith-irrational/>.
Occasionalism — a theory claiming that God is the only true cause of changes in the world. For example, when you high-five me, you’re not really the cause of the stinging sensation I experience. God is the cause. Your high five is just the occasion on which God causes it.
Interactionism — a theory claiming that things in the world can truly cause changes in each other. For example, when you high-five me, you truly cause me to experience a stinging sensation in my hand.
Substance Dualism — a theory claiming that the mind (or soul) and body are two distinct and very different things.
Body — what it sounds like! The body is the physical part or aspect of a thing and has characteristics like shape, size, etc.
Soul — that part or aspect of a thing involving mental aspects of their existence, e.g., thoughts, feelings, decisions, etc. The “soul”, in this sense, is more or less just the mind.
Causal Interaction — When one thing acts (i.e., itself does something) and in so acting makes another thing change. For example, when you high-five me, you cause me to experience a stinging sensation in my hand.
God as God – The phrase “God as God” is basically a synonym for “God the subject.” In other words, it refers to God precisely in God’s status as an incomprehensible divine Other.
Incarnation – The Christian doctrine of the incarnation is the notion that the word of God became fully human in the person of Jesus of Nazareth. It is closely associated with the doctrine of the trinity, which asserts that God the Father, God the Son (Jesus as the word made flesh), and God the Holy Spirit are one God.
Religious Fanaticism – In Feuerbach’s use of the term, a religious fanatic is someone who is unwaveringly faithful to God as an utterly mysterious superhuman being. They subordinate other things—especially the love of other humans—to submission before this divine other.
God the Subject – When Feuerbach refers to God as a subject, he is referring to the commonplace religious belief that God is a being who has various attributes, like a loving nature.
Faith Separates Man From God – Faith separates God from man in this sense: it treats God as a mysterious other, a being radically distinct from us.
Faith – Belief in and fidelity to a transcendent divine subject like God.
Orthodoxy – Orthodoxy refers to “right belief,” and it is concern with identifying heresies and ensuring that people believe and practice correctly.
Indirect Form of Self-Knowledge – Feuerbach’s view is that religious belief is a naive way of relating to our human nature and its perfections. It is naive or childlike because it treats these as external realities that belong to God. He believes a mature and contemplative person realizes these don’t belong to God, but rather to our species, abstractly conceived.
Above the Individual Man – The human perfections are “above the individual” insofar as no particular individual ever perfectly realizes them. They are abstractions.
Divine Trinity – Feuerbach is having fun here. He is using the theological phrasing of the Trinity to talk about human perfections. In calling reason, love, and freedom of the will “divine,” he means they are absolutely good; they are activities whose goodness is intrinsic to their practice or exercise. This isn’t a novel philosophical view. For example, Immanuel Kant argued that autonomy or a good will is the only thing which is unconditionally good.
Perfections – The end to which a faculty or power is ordered. For example, omniscience would be the perfection of the intellect. Traditionally, God is said to possess all perfections.
Love – When Feuerbach writes about love, he is referring to unconditional concern for others and the desire for fellowship with them. He is here asserting that love, understood in this sense, is the perfect activity of the affective faculty. In other words, our feelings and passions are fully actualized and engaged in an intrinsically valuable activity when we genuinely love others.
Infinite – The infinite is whatever can be understood as unbounded or unlimited. Human nature in the abstract is unbounded and unlimited. It is only bounded or limited in its concrete form as it is realized by particular material individuals.
Higher Consciousness – The sort of consciousness that mature human beings possess, but which other animals do not. It is “higher” than animal consciousness because it involves thinking abstractly about the form or essence of things.
Science – Feuerbach uses the term science in its classical sense, meaning systematically organized knowledge. Any body of knowledge founded on an understanding of first principles and the essences of things is a science in this sense.
Popular Sovereignty – The view that a government’s authority to rule comes from the people, making a ruler subject to the will of their citizens.
The Divine Right of Kings – The theory that kings are chosen by God and thus that political revolt is a rebellion against the will of God.
Synthesis – The prefix ‘syn-’ means “together,” so a synthesis “brings together” or combines elements of both a thesis and its antithesis.
Antithesis– An antithesis is the contradiction of a thesis. For example, internationalism could be understood as the antithesis of nationalism.
Thesis – In Hegelian terms, a thesis can be understood as a position or theory. Examples include any of the “-isms” that we discuss in science, history, and philosophy, such as Darwinism, capitalism, nationalism, etc.
Progressor’s Temptation – a unique temptation for those making progress in which pride impedes their further progress and leads to backsliding.
Progressors – those who are not yet expert Stoic practitioners, but who are also aware of the fact that they must change their lives in that direction. They are working on making progress.
Intellectualism – the philosophical view that our motivations and emotions are all judgments. The reason why you do something, your motivation, is because you believe it’s the right thing to do. The reason why you feel good or bad about something, an emotion, is because you believe that something good or bad happened to you.
Duties – acts of service, obedience, and respect that we owe to each other. The duties we owe to each other depend on what kind of relationship we have.
Askeses – exercises of Stoic thought and practice that make the lessons and habits of Stoic philosophy second-nature for Stoic practitioners.
Externals – things that are not under our control but that are all-too-easily confused with things that should be important to us, like wealth, status, and pleasure. Too many people believe externals like these are necessary for the good life, and the Stoic path is to focus not on these things but rather what is up to us.
The Fundamental Division – the division between things that are under our direct control and those that are not. The important lesson is to care only about the things we can control.
The Greatest Happiness Principle – A principle which says that actions are right insofar as they promote happiness and wrong insofar as they promote unhappiness
Higher and Lower Pleasures – Types of pleasures that differ in terms of their quality. Things like food and drugs create lower pleasures. Things like intellectual pursuits and doing the right thing create higher forms of pleasure.
The Doctrine of Swine – An objection that utilitarianism entails that if people would be happy rolling in mud, that’s what would be morally best for them to do, so we should reject the theory.
Utilitarianism – A normative theory of which actions are right or wrong. Utilitarianism says the right action is that which maximises utility.
Jeremy Bentham – Considered by some as the father of utilitarianism, Bentham was a moral philosopher and one of John Stuart Mill’s teachers
Epicurus – an ancient Greek philosopher and one of the first to advocate that the ultimate good is experiencing pleasure and avoiding pain.
Utility – The thing that is ultimately valuable in itself. For Mill, this is happiness, which he then understands as pleasure and the absence of pain.
Contract Theory – a modern political theory identifying consent as the sole justification for government. Contract theory is associated with Thomas Hobbes (1588-1679), John Locke (1632-1704), Jean Jacques Rousseau (1712-1778), and more recently, John Rawls (1921-2002)
Prejudice – a foundational, strongly held, unreasoned (but not necessarily irrational) moral opinion or belief. We might believe, for example, that parents have special obligations towards their own children.
A Priori – a philosophical term of art meaning (in Latin) “prior to experience,” which refers to knowledge that is innate or arrived at purely through reasoning, like the truths of mathematics.
Rights – moral claims invoking immunity from (or entitlement to) some specific treatment (or good) from others. Commonly recognized rights include the right to free speech or the right to healthcare.
Reform – a change in the social order that originates from the existing character of society. An example would be market-based healthcare reform in a capitalist society.
Conservatism – a modern political ideology that aims to preserve and promote the existing (or traditional) institutions of society. These institutions typically include the rule of law, property, the family, and religion.
Contingent Being – A being that can fail to exist. Its existence is not guaranteed. This being might come to exist or it might not.
Necessary Being – A being that can’t fail to exist. Its non-existence is impossible. This also means that such a being has always existed.
Want to read more about why the infinite regress option doesn’t work in the Second Way? Check out Sean Floyd’s entry in the Internet Encyclopedia of Philosophy.
Efficient Cause – An efficient cause is something that directly makes another thing exist or move. An example of this is when I kick a ball down a hill. I am the efficient cause of the ball rolling down the hill because I make it move down the hill.
Infinite Regress: Begin with some fact. We begin to explain that fact by appealing to another fact, where these facts are related by either causality or dependence. To create the regress, you keep appealing to more and more facts about causality and dependence without end.
Actuality – An ability or action something is currently exercising. Imagine that I am sitting comfortably at my desk, and then I stand up to take a break from reading. In this case, I am now actually standing.
Potentiality – What something has the capacity to do, but isn’t currently doing. Imagine I am sitting comfortably at my desk. Even though I’m not currently standing, I have the capacity to be standing. So, even while I’m not standing, I have the potential to stand.
Theists and Non-Theists – A theist is someone who believes that God exists, while a non-theist does not. Non-theists include atheists, who believe that God does not exist, and agnostics, who are uncertain about whether God exists.
Glaucon – one of Plato’s brothers and one of Socrates’ main interlocutors in the Republic dialogue. In that dialogue, he challenges Socrates to provide a compelling justification for why one should be a just person beyond merely following conventions or avoiding punishment. This sets up Socrates’ defense of justice as intrinsically worthwhile. Throughout the Republic, Glaucon prods Socrates to fully explain his theories of the ideal society, philosopher-kings, and the Form of the Good.
Aristotle – a Greek philosopher (384-322 BC) who studied under Plato and went on to be one of the most influential philosophers to ever live. Simply called “The Philosopher” by Thomas Aquinas and others in the medieval period, Aristotle’s views would eventually be synthesized with Christian theology, laying the intellectual foundation for later scholarly developments in Western Europe.
Understanding – Socrates describes education as turning one’s “understanding” in the right direction. The word “understanding” here translates the ancient Greek term “to phronēsai,” which means “understanding,” “being conscious,” or “having insight.” People who are wicked focus their “understanding” on how best to accomplish their selfish and narrow desires. Those who are wise, in contrast, have learned to focus their “understanding” on what is truly good and beneficial.
The Form of the Good – Socrates characterizes the ultimate goal of education as coming to know “the Form of the Good.” The Form of the Good is his technical term for the meaning of goodness: what it is to be good. Socrates is clear that this “knowledge of the Good” is not simply theoretical knowledge, but also knowledge in the sense of “knowing how”: knowing how to achieve what’s good, to do what’s good, to accomplish what’s good. Mere “book knowledge” or simply being smart is not enough.
The Intelligible – Socrates uses “the intelligible” to name the aspects of the world that we can only grasp through thinking or insight. With my eyes I can see the tree outside my window, but what it means to be a tree is something I can only comprehend in thought. Likewise, I can see the people around me, but human nature, human dignity, and what it means to be human is something I can only grasp conceptually. “The intelligible” is the world insofar as it “makes sense” and can be comprehended.
The Visible – By “the visible,” Socrates means those aspects of the world we can perceive with our five senses and our imagination—those aspects of the world we can see, hear, taste, smell, touch, and imagine. For example, with my eyes I can see the sky, trees, people around me, and so on as visible things. “The visible” is the world insofar as it can be perceived and imagined.
Education – Socrates says that the allegorical story he tells represents the effect of education on human nature. “Education” here is a translation of the ancient Greek word “paideia,” which means “education” in the widest sense of the term. “Paideia” doesn’t mean “education” in the sense of going to school or getting good grades. Instead, it refers to the process of becoming a wise, intelligent, good, and well-rounded human being.
Allegory – An allegory is a symbolic narrative where characters, events, and/or settings represent abstract ideas or convey deeper meanings beyond the literal story. Socrates tells such a symbolic narrative in the passages below. The characters, events, and setting of his narrative symbolize the effect of what he calls “education.”
Self-knowledge – Knowledge of the contents of one’s own mind, such as one’s own beliefs and desires. Self-knowledge can be gained through introspection, that is, by reflecting on what one thinks and experiences. Some philosophers believe that self-knowledge has special properties that our knowledge of the external world lacks, such as being clearer, more reliable, or more valuable.
Dualism – The view that the mind is entirely distinct from the body. This view is usually contrasted with different kinds of monism, which hold that the mind is ultimately just a part of the body (materialism) or that the body is ultimately just a part of the mind (idealism). Dualists hold that the mind and the body are fundamentally different aspects of reality, and both categories are needed to properly describe the universe, especially the human person.
The Self – What the ‘I’ in ‘I am, I exist’ refers to; the part of you that really makes you you. Many philosophers have provided rich accounts of what the self ultimately is, including the soul, the mind, one special feature of the mind (such as consciousness), a mixture of all these elements, or perhaps a mere illusion.
The ‘Cogito’ – Descartes’ famous claim ‘I think, therefore I am’ is often referred to as the cogito. The name comes from the Latin rendering of this phrase, which is ‘cogito, ergo sum.’ Descartes held that one can always believe this proposition with certainty. We cannot doubt our own existence, so the cogito survives his exercise of intense doubt. The cogito appears several times in Descartes’ writings, and he often phrased it slightly differently each time. It appears in the Second Meditation as ‘I am, I exist.’
Certainty – When one believes something with certainty, one is maximally confident that it is true. A certainty is something that is beyond dispute or immune to doubt. Although this captures the basic idea, like many epistemological notions, clarifying precisely what the notion of certainty amounts to is an ongoing area of philosophical research.
Vice – A bad habit that we learn over time through instruction or instinct and that we develop through repetition. What makes the habit bad is that, once we have that habit, our tendency is to do the incorrect thing in certain types of situations. We may choose to do something entirely uncalled for in that situation, or we may act at the wrong time, in the wrong way, to the wrong degree, or with the wrong attitudes, or for the wrong reasons.
Relative Mean – The “Goldilocks amount” of some type of action or emotion. When you act in this way, according to Aristotle, you act exactly as is required under the current circumstances. This means that you do what is called for by the situation at hand, rather than doing something too extreme or not doing something extreme enough. You do something in the moderate amount (the mean amount) relative to the specific situation you are in when you need to act.
Excellence/Virtue – A good habit that we learn over time through instruction and repetition. What makes the habit good is that, once we have that habit, we have a strong tendency to do the right thing at the right time, in the right way, to the right degree, with the right attitudes, whenever we are confronted with a situation that we know calls us to exercise that habit.
Doxastic Voluntarism – the view that we have at least some control over what we believe.
Evidence – information that increases the probability that a claim is true.
Sufficient – enough of something for a particular purpose. Whether something is sufficient is context-dependent.
Solon – In the Histories of Herodotus, Solon visits Croesus, the king of Lydia. Even though Croesus shows Solon all of his wealth, Solon refuses to call him the happiest man who ever lived because he does not know how Croesus will die
Priam – According to Greek mythology, Priam was the final king of Troy during the Trojan War. Despite his wealth and political power, he was killed by Achilles’ son Neopotolemus during the Sack of Troy
Virtue – The consistent and reliable tendency to perform one’s function excellently. When a person has a certain virtue, like courage, they have spent time developing the habit, in this case reacting to danger well, using their human abilities. The virtues then make it possible for us to live a life of flourishing
Sardanapalus – An Assyrian king described by the historian Diodorus as living a life of extreme decadence. Sardanapalus indulged himself with food, alcohol, and many concubines, even going so far to say that physical gratification is the purpose of life. Chrysippus said that, on his tomb is inscribed the following: “Though knowing full well that thou art but mortal, indulge thy desire, find joy in thy feasts. Dead, thou shalt have no delight […] I have only what I have eaten, what wantonness I have committed, what joys I received through passion; but my many rich possessions are now utterly dissolved.”
Function – the characteristic activity of a given thing which makes it what it is. The function of a knife is cutting, while the function of a heart is to pump blood
Eudaimonia – Frequently translated as ‘happiness’, eudaimonia means the attainment of active human flourishing, and is the end Aristotle identifies as humanity’s highest final good
Final Good – A good that we pursue for its own sake. Common examples of final goods include happiness, knowledge, and friendship
Instrumental Good – A good that we pursue for the sake of some other good. A common example is money, as money allows us to purchase other kinds of goods
Anytus – an Athenian politician, war general, and one of the primary accusers behind Socrates’ prosecution. Anytus feared that Socrates would undermine the young Athenian democracy he had helped create and defend
Oracle of Delphi – the high priestess at the temple at Delphi, the oracle was one of the most sought after seers of the ancient world and was thought to relay messages from the god Apollo
Chaerephon – an ancient Greek from the city Sphettus, Chaerephon is remembered as a loyal friend of Socrates, also making an appearance in two other Platonic dialogues, the Charmides and the Gorgias
Meletus – A poet and citizen of Athens and one of Socrates’ accusers. Amongst other things, Meletus accused Socrates of corrupting the youth
Apollo – the ancient sacred site Delphi was dedicated to the god Apollo, an ancient Greek god and the god that Socrates refers to throughout the Apology
Virtue – a character trait, acquired through habitual practice, that enables one to act well. The virtues can also be thought of as excellences of human character, as they make it possible for us to live a life of flourishing. Examples of the virtues include courage, prudence, and justice
The Evil Demon Argument – Argues that we cannot hold any of our beliefs with certainty because we could be radically deceived by an evil demon. A classic argument given by Descartes for doubting the reliability of almost all of our beliefs
Philosophical Skepticism – The position that we do not know many things that we ordinarily take ourselves to know
A Posteriori Knowledge – Knowledge that can only be acquired through having particular, concrete experiences. Such knowledge can be gained simply through our everyday experiences, or through more complex means like controlled scientific experiments
A Priori Knowledge – Knowledge that can be gained without having any particular concrete experiences. Such knowledge is typically gained by rational insight or intuition
Cartesian Method of Doubt – A process employed by René Descartes of rejecting all beliefs that he had at least some reason to doubt in order to see if he had any beliefs that he could know with certainty
Revelation – Theological truths that have been made known by means of some religious text, testimony, authority, or experience, or the act or process in which such truths are made known.
Rationalism – The view that the only reliable means of coming to know truths about God is reason. As a result, what we might otherwise believe by means of faith ought to be disregarded or even rejected in favor of what we must believe by means of reason.
Fideism – The view that the only reliable means of coming to know truths about God is faith. As a result, what we might otherwise believe by means of reason ought to be disregarded or even rejected in favor of what we must believe by means of faith.
Faith – The act of accepting a proposition as true for which there is less than demonstrable evidence, which rises above mere opinion but falls short of logical or scientific demonstration. Faith can also refer to a particular religious tradition or the body of beliefs that are central to that religious tradition.
Virtue – a character trait, acquired through habitual practice, that enables one to act well. The virtues can also be thought of as excellences of human character, as they make it possible for us to live a life of flourishing. Examples of the virtues include courage, prudence, and justice
Socratic Ignorance – an awareness of one’s own ignorance, and the reason that Socrates was deemed wise by the Oracle of Delphi. A person who lacks Socratic Ignorance may believe they know many things they actually don’t, leading them to overestimate how well they understand the world
Apology – a formal defense of justification of an action or belief. A Christian apologist, for example, is someone who defends their faith and seeks to justify it through an appeal to reason.
