Keep It Simple
Thomas Aquinas's Summa Theologiae, Part 1, Question 3

Table of Contents

Picture of <b>James Kintz</b><br><small>Associate Professor of Philosophy, Dominican School of Philosophy and Theology</small>
James Kintz
Associate Professor of Philosophy, Dominican School of Philosophy and Theology

Warm-Up: The Absolute Perfection of God

Many people believe in God, but it is not always clear what we should believe about God. Some have thought that whatever we can know about God must be learned from religious texts, such as the Bible or the Quran. But philosophers have often argued that we can also discover certain truths about God through the use of reason. For example, a number of philosophers have defended the claim that God is perfect – in fact, as perfect as a being could be. That is to say, if there is a God, then God could not be any more perfect than he is, and there could be no being more perfect than God.

But if we accept this, then new questions arise that demand investigation. For instance, if God is absolutely perfect, then could he be composed of different parts like human beings are? Or could God have any features that are not essential to him? This is certainly the case for human beings – a person who has long hair and a talent for playing music would still be the same person even if he cut his hair and could not play music. And there are a host of similar features or abilities that we can gain or lose while still remaining the same person. But could this be true of God as well? Or, like us, could God exercise one of his abilities some of the time but not at other times, such as when a person who can play the piano chooses to read a book instead?

Thomas Aquinas addresses questions such as these in this section of the Summa Theologiae, arguing that God is simple, which means that God has no parts, nor does he have any attributes that are not included in his essence. And this is largely because of the sort of being that God is. In this entry, we will look at some of Aquinas’s primary arguments for why we ought to think of God as simple. 

Introduction

Thomas Aquinas (born in either 1224 or 1225; died in 1274) was a medieval Italian philosopher and theologian who studied under Albert the Great. Because he was a particularly reticent student, and because he was reported to be a large person, he was nicknamed “The Dumb Ox.” His teacher, however, recognized his intellectual abilities and allegedly stated that when he engages in the academic discussion “this Dumb Ox shall bellow so loud that his bellowings will fill the world.” And Albert was right: Aquinas was one of the most influential philosophers in the medieval world, and even though his life was relatively short he wrote an astounding number of philosophical and theological works that have an enduring influence on scholars into the present day.  

While Aquinas addressed many important topics in both philosophy and theology, one of the issues for which he is most famous concerns his arguments in defense of what is now known as “classical theism,” which includes a commitment to the doctrine of divine simplicity. In a nutshell, the doctrine of divine simplicity claims that God is not composed of any parts. Below you will read some of Aquinas’s chief arguments from the Summa Theologiae in defense of this doctrine.

It is worth noting at the outset that medieval philosophers wrote in a way that might appear strange to contemporary readers. They would focus on a disputed question, offering their own account on a controversial issue (for Aquinas, this can be found in the section following the “On the contrary” and “I answer that” or “Reply”), but in the process they would also present common and/or challenging counterarguments to their own position (found in the objections), as well as their responses to those counterarguments (found in the replies to objections). In what follows we will focus on the corpus (the “I answer that” section) of four of the eight articles that comprise Summa Theologiae I, Question 3, but readers are encouraged to dig deeper by reading this Question in its entirety, including the objections and replies, found here.

Key Concepts

Essence: The “what it is to be” of a thing. For example, the essence of a human being is to be a rational animal, and the essence of a cheetah is to be the fastest land animal.

Subject/Suppositum: Something or someone that can bear properties but is not itself a property that something else can bear. Dylan can have properties, like being short or being musical, but no one can have Dylan as a property. 

Property: A feature that an object has. For example, a ball could be orange, which means that the ball has the property of orangeness. In many cases a property can be gained or lost. The ball could be painted green, in which case it would gain the property of greenness and lose the property of orangeness.

Accident/accidental property: A property that something can possess or not possess while still remaining the thing that it is. For example, Dylan could grow taller, or he could stop being musical, without becoming a different person. By contrast, rationality is an essential property of Dylan, since being rational is part of the “what it is to be” of a human being.

Actuality: The being, or act of being, of a thing. For example, hot water is actually hot (the water is hot), even though it is potentially cold. Likewise, a boy is actually a human being (he is a human being), even though he is also potentially a full-grown man (and he will still be an actual human being when he becomes a full-grown man).

Potentiality: Ways a given thing can become different from the way it is now. For example, cold water is potentially hot, since it can be heated up, and an acorn is potentially an Oak tree since it can grow to full size under the right conditions. 

Constituent Principles: Parts of a material object that cause the object to be the sort of thing that it is, but that cannot be removed from that object (in the way that some properties can be gained or lost). For Aquinas, this would include things such as form (the structure of a material object) and matter (that which is structured). For example, Dylan’s form is his soul, and his matter is his body. His soul and body are distinct, but Dylan could not exist if he were not composed of both. 

Everybody Needs Somebody… Except God

If God is simple – which means that he has no parts – then he cannot have a body. Here is Aquinas’s argument to show this:

Question 3, Article 1

First, no body is in motion unless it be put in motion, as is evident from induction. Now it has been already proved (Question 2, Article 3) that God is the First Mover, and is Himself unmoved. Therefore it is clear that God is not a body. Secondly, because the first being must of necessity be in act, and in no way in potentiality. For although in any single thing that passes from potentiality to actuality, the potentiality is prior in time to the actuality; nevertheless, absolutely speaking, actuality is prior to potentiality; for whatever is in potentiality can be reduced into actuality only by some being in actuality. Now it has been already proved that God is the First Being. It is therefore impossible that in God there should be any potentiality. But every body is in potentiality because the continuous, as such, is divisible to infinity; it is therefore impossible that God should be a body.

The first argument that Aquinas gives begins with the observation that everything in the natural world either undergoes change or is at least subject to change. But anything that changes – or is put in motion, as Aquinas puts it – must be changed by something else.

For instance, if a baseball player hits a ball, then he puts the bat into motion which in turn puts the ball into motion. But there is also a sense in which the baseball player himself was put in motion by his parents, who were put in motion by their parents, and so on. Clearly, this cannot go on forever, so Aquinas thinks that there must be something that can cause motion or change but is not itself put in motion or changed by anything else. And that something is God. But since all bodies – that is, anything that exists in the physical universe – are either in motion or potentially in motion, then it cannot be the case that God has a body.

The second argument he gives depends on an important distinction between potentiality and actuality. While the argument here is somewhat complex, we can get the gist of it by thinking about the way that potentiality depends on actuality. A cheetah has the potentiality to run fast when she is chasing a gazelle, but she has this potentiality because she is already actually a cheetah. Likewise, a small oak tree has the potentiality to grow into a large oak tree because it is already actually an oak tree. To have a potentiality of some kind thus depends on something that is already actual in some way.

But notice that neither the cheetah nor the oak tree exist on their own – both of them were caused to exist by something else (parents, an acorn). This is to say: they potentially existed before they actually existed, which implies that they must have depended for their coming into being on something else that already actually existed (again, parents, an acorn).

But, as Aquinas notes, God is the “First Being,” so he could not depend on anything else for his existence like the cheetah or the oak tree do. Likewise, because he is the First Being he cannot have any potentiality. After all, if an oak tree actualizes its potential to become large, this is because something else acts on it to help it grow, such as the sun or proper rainfall. But as the First Being there is quite literally nothing else that could act on God to actualize any potentiality. So, Aquinas insists that God has no potentiality whatsoever. Since any object that has a body has potentiality, and since God does not have any potentiality, Aquinas concludes that God does not have a body.

Do It Yourself!

Embodiment, Change, and Experience

While Aquinas’s arguments here are from the Middle Ages, if he is right then they ought to hold today. So, using your own rational skills, do you think that it is plausible to suppose that God has a body (and, therefore, parts)? One way to consider this is to think about your own body – to be human is to be an embodied creature, which is to say that the way we are, as well as the way we experience the world around us, is a result of having (or being) a body. But we undergo change all the time, and we experience change in the world. Is it plausible to think that the same could be true for a perfect being like God? And, if God does not have a body, what other sorts of conceptual commitments would follow? After you have worked through the rest of Aquinas’s arguments in favor of divine simplicity, return to questions such as these and see where reason leads.

It Is What It Is

For Aquinas, things in the natural world have essences. That is, there is a “what it is to be” of a given thing that makes it distinct from other kinds of things. To be a human being, for example, is to be a rational animal, and to be a cheetah is to be the fastest land animal. And anything that fits within the same category has the same essence. But things such as humans and cheetahs have features in addition to their essence. Dylan is a human being with a human essence, but he is not the only human being – Paul is also a human being with the same essence as Dylan. Furthermore, Dylan may have a beard while Paul is clean-shaven, so they have different properties even though they share the same essence. So, Dylan and Paul are not identical to the human essence. But for Aquinas, this basic principle that existence and essence are distinct does not hold for God:

Question 3, Article 3

God is the same as His essence or nature. To understand this, it must be noted that in things composed of matter and form, the nature or essence must differ from the suppositum, because the essence or nature connotes only what is included in the definition of the species; as, humanity connotes all that is included in the definition of man, for it is by this that man is man, and it is this that humanity signifies, that, namely, whereby man is man. Now individual matter, with all the individualizing accidents, is not included in the definition of the species. For this particular flesh, these bones, this blackness or whiteness, etc., are not included in the definition of a man. Therefore this flesh, these bones, and the accidental qualities distinguishing this particular matter, are not included in humanity; and yet they are included in the thing which is man. Hence the thing which is a man has something more in it than has humanity. Consequently humanity and a man are not wholly identical […] On the other hand, in things not composed of matter and form, in which individualization is not due to individual matter – that is to say, to this matter – the very forms being individualized of themselves – it is necessary the forms themselves should be subsisting “supposita.” Therefore “suppositum” and nature in them are identified. Since God then is not composed of matter and form, He must be His own Godhead, His own Life, and whatever else is thus predicated of Him.

Argument

God is Identical to His Essence

Whenever something has a body – that is, whenever it is composed of matter and form – that thing always has accidental properties. This means that we can draw a distinction between that thing and its essence. But in the text above Aquinas argues that no such distinction can be drawn between God and his essence. One way we might simplify and formalize the foregoing argument is as follows: 

P1: If something has properties, or attributes, that are not included in its essence, then that thing is not identical to its essence. 

P2: When something has a property that is not included in its essence, this is because that thing is partially composed of matter (e.g., humans are composed of a body and a soul – the former is matter, the latter is form). 

P3: But God is not composed of matter. 

P4: If God is not composed of matter, then he could not have any properties that are not included in his essence.

P5: Since God does not have any properties that are not included in his essence, then there is no way to distinguish God from his essence.  

P6: If it is impossible to distinguish one thing from another (in this case, God and his essence), then those things are not distinct.

C: Therefore, God is not distinct from his essence, but is identical to his essence.

Premise 1 states what appears to be a basic fact about things in the material world. Dylan (the subject/suppositum) has properties that are not included in the essence “human,” such as being short or being musical. To have these accidental properties means that Dylan would still count as a human being even if he were not short, and even if he were not musical. Since Dylan has properties that are not included in his essence, it could not be the case that he is identical to his essence. And the same would be true of anything else in the created world.

Premise 2 states that accidental properties are a result of having matter (i.e., having a body), which also seems largely uncontroversial since something could only have properties such as “shortness” or “musicality” if that thing has a material body. Premise 3 states something that Aquinas has already established in Article 1, viz., that God does not have a body. Since God does not have a body, then as premise 4 states he could not have any properties in addition to what he already has in virtue of his essence.

In light of this, Premise 5 states that there is no way to distinguish God from his essence, as we can for beings like Dylan, and premise 6 notes that when it is impossible to distinguish one thing from another, then that is because those two things are not actually distinct. In other words, two things that may have appeared to be distinct are actually one and the same thing. Hence, God is not separate or distinguishable from his essence, but is identical to his essence.

To Be or… To Be?

Given what we learned in Article 3, it might initially appear strange that Aquinas is discussing essence and existence again in Article 4. But here he tackles this distinction by focusing on existence rather than essence. As we saw above, in most things essence and existence are not identical, but this is not the case for God, who is identical to his essence. And, when Aquinas focuses on the existence side of the essence-existence distinction, it turns out that God is identical to his existence as well. In other words, God just is his own being.

Question 3, Article 4

God is not only His own essence […], but also His own existence. This may be shown in several ways. First […], if the existence of a thing differs from its essence, this existence must be caused either by some exterior agent or by its essential principles. Now it is impossible for a thing’s existence to be caused by its essential constituent principles, for nothing can be the sufficient cause of its own existence, if its existence is caused. Therefore that thing, whose existence differs from its essence, must have its existence caused by another. But this cannot be true of God; because we call God the first efficient cause. Therefore it is impossible that in God His existence should differ from His essence. Second, existence is that which makes every form or nature actual; for goodness and humanity are spoken of as actual, only because they are spoken of as existing. Therefore existence must be compared to essence, if the latter is a distinct reality, as actuality to potentiality. Therefore, since in God there is no potentiality […], it follows that in Him essence does not differ from existence. Therefore His essence is His existence. Third […], that which has existence but is not existence, is a being by participation. But God is His own essence […]; if, therefore, He is not His own existence He will be not essential, but participated being. He will not therefore be the first being—which is absurd. Therefore God is His own existence, and not merely His own essence.

Main Idea

The Cause That Needs No Cause

There’s a lot to unpack here, but the gist of what Aquinas is getting at is this: when the essence and existence of a thing come apart, as they do in all created things, then something external to the created thing must cause it to exist. In such cases, Aquinas identifies two options: 1) it is caused by its constituent principles or 2) it is caused by some external agent. The former isn’t possible, since for Aquinas the constituent principles of a particular thing exist because the thing itself exists. For example, because Dylan has a human soul which structures the matter he is composed of, he has the capacity to laugh. His soul or structure is what causes his capacity to laugh. But his structure itself could not cause Dylan to exist, because neither Dylan’s soul/structure, nor his body, could exist before Dylan exists. Dylan just is his body and soul. 

In light of this, if a thing’s existence is caused then it must have been caused by some external agent. And insofar as a created thing receives its existence from something else, that thing cannot be responsible for its own existence, but has what Aquinas calls “being by participation,” which means that its status as an existing thing involves a dependence on something else (both for its coming into existence and for its staying in existence). And when this is the case, there is a distinction between a thing and its existence.

Think about it like this: I can think about Dylan independently of whether Dylan exists – in fact, we have been doing precisely this throughout this whole entry! So, there are questions that we can ask about Dylan, and then there is the further question as to whether Dylan actually exists, which suggests that Dylan is not identical to his existence. But, of course, this could not be the case for God, because as the Cause of all things God neither has a cause nor could have a cause. Since God’s existence could not have been caused by anything external, there cannot be a distinction between God and God’s existence (as there is for all created things). Aquinas thus concludes that God must be identical to his existence. 

Here’s a shortcut to get to the same conclusion. Notice that in Article 3 Aquinas argued that God is identical with his essence. In other words, God just is his essence, which is to say that his essence and his existence are the same thing. If essence and existence are the same thing for God, and if God is identical to his essence, then he is also identical to his existence.

Accidents Happen…

All physical beings have both essential properties and accidental properties. For example, rationality is an essential property of being a human, but being short is an accidental property of a given human, which is to say that Dylan would still be a human even if he wasn’t short. But, for Aquinas, God does not have any accidental properties:

Question 3, Article 6

From all we have said, it is clear there can be no accident in God. First, because a subject is compared to its accidents as potentiality to actuality; for a subject is in some sense made actual by its accidents. But there can be no potentiality in God, as was shown (Question 2, Article 3). Secondly, because God is His own existence; and […] although every essence may have something superadded to it, this cannot apply to absolute being: thus a heated substance can have something extraneous to heat added to it, as whiteness, nevertheless absolute heat can have nothing else than heat. Thirdly, because what is essential is prior to what is accidental. Whence as God is absolute primal being, there can be in Him nothing accidental. Neither can He have any essential accidents (as the capability of laughing is an essential accident of man), because such accidents are caused by the constituent principles of the subject. Now there can be nothing caused in God, since He is the first cause. Hence it follows that there is no accident in God.

Here, Aquinas argues that God has no accidents. When he was a baby, Dylan may have had the properties of being small and non-musical. But “small” and “non-musical” are accidental properties that he will eventually lose when he grows up and develops his musical abilities. But even Dylan, once he is full-grown, will still have a number of accidental properties (e.g., being clean-shaven, being able to play the piano), and any accidental properties can be gained or lost without impacting his status as a human being.

In light of this, it is clear that accidental properties are tied up with potentiality. But since God has no potentiality, he can have no accidental properties. Likewise, God could not become more fully what he is, because he is already perfect in every possible respect. Finally, like anything with potentiality, for that potentiality to become actual something external that is already actual must move that thing from potentiality to actuality. But God is the First Cause, so there is nothing that could act on God. Thus, there could be no accidents in God. 

Connection

The Unity of Divine Attributes: A Lesson from Les Misérables

The claim that God has no accidents has some important implications. For example, we saw that God is identical to both his essence and his existence, and for similar reasons God must also be identical to all of his attributes. Further, since God has no potentiality, it could not be the case that God exhibits some of his attributes at some times but not at others, but, as identical with all of his attributes, God is always perfectly exhibiting any attribute that he possesses. 

Such implications have struck many as odd, perhaps even implausible, for a number of reasons. For example, among other things, God has attributes that are not obviously the same thing, such as being both omnipresent and omnibenevolent. But there is no overlap between these distinct attributes, and having one does not entail having the other. Further, not only does God possess seemingly distinct attributes such as these, but he also appears to possess contradictory attributes, such as being perfectly just and also perfectly merciful. But if it is the case that God has no accidents, then any attributes that we identify in God, including the seemingly contradictory ones, are included in God’s essence/existence, and are always fully actualized. 

How can this be? These sorts of claims are deeply puzzling, and many philosophers of religion reject the doctrine of divine simplicity because it appears so implausible on such points. 

Yet while it is impossible to address this fully here, we nevertheless have resources at our disposal to mitigate such worries. Consider an example from Victor Hugo’s Les Misérables. Jean Valjean is sent to prison for stealing bread to feed his starving family, and over many years in jail he has grown deeply bitter at the injustice of his imprisonment. But, eventually, Valjean gets out of prison, and as he travels through the countryside he happens upon the home of a bishop, who, unlike everyone else that he has encountered, treats him with great kindness and compassion, even inviting him to stay the night in his own home. But despite such treatment, Valjean secretly steals the bishop’s silver and escapes in the middle of the night. He is soon caught, and the silver is recognized as belonging to the bishop, so the authorities bring him back to the bishop’s home so that the bishop can confirm that it is his silver and press charges. But rather than prosecuting Valjean, the bishop once again greets Valjean with great kindness and insists that he gave the silver to Valjean as a gift; he even hands him the matching silver candlesticks, claiming that he forgot them in his haste to leave. 

The bishop would have been well within his rights to send Valjean back to jail. This would have been perfectly just. But given Valjean’s history, if he had done this Valjean would have only become more bitter, likely seeing himself as, for example, having had a right to take the silver, perhaps as recompense for his previously unjust incarceration. To put this another way, while another imprisonment may have been just, Valjean would not have recognized the justice of his new incarceration but would have viewed himself as a victim of an unfair system. This would in turn have contributed to his inability to recognize his own guilt. But by responding to this betrayal and theft with a profound kindness – by showing him mercy – the bishop impressed upon Valjean that he was guilty, and Valjean felt his guilt far more keenly than he would have if the bishop had acted with justice instead of mercy. In fact, if we take Valjean’s disposition and history into account, and if we think that for justice to occur it would be better for the wrongdoer to recognize his guilt, then if the bishop had prosecuted Valjean it would have prevented justice from obtaining. Indeed, given the details of the situation, by acting with mercy the bishop was also acting with justice. 

What this example intends to illustrate is that in one act the bishop was both merciful and just – merciful in that he did not require Valjean to pay for his crime, and just in that showing mercy was the only way to “punish” Valjean and impress upon him his guilt. So, even though justice and mercy appear to be contradictory, they can be complementary, and in some cases they can be a single action. While this does not show how we can reconcile all of God’s seemingly diverse attributes into a single act, it should at least hint at a means by which we can avoid some of the objections to the claim that God has no accidents.  

Summary

The doctrine of divine simplicity is, at least in many respects, not such an easy idea to wrap our heads around. But while we need to take our time in considering and assessing Aquinas’s arguments in support of this doctrine, the bare essentials are relatively straightforward. To claim that God is simple is just to say that God has no parts of any kind. And this must be true given that Aquinas understands God as Pure Actuality – that is, he has no potentiality – and to have parts of any kind would entail potentiality.

There are other important details, of course. For instance, that God is identical with his essence and with his existence. But the doctrine of divine simplicity for Aquinas boils down to the central claim that God is already as perfect as he could be, and any composition or complexity in God would make him less perfect, which is impossible. Pretty simple, right?

Want to Learn More?

If you would like to pursue Aquinas’s conception of divine simplicity further, as well as contemporary developments of this doctrine, read the articles “Divine Simplicity” on the Internet Encyclopedia of Philosophy and “Divine Simplicity” on the Stanford Encyclopedia of Philosophy. Also, see chapter 3 of Brian Davies book The Thought of Thomas Aquinas, as well as chapter 3 of Eleonore Stump’s book Aquinas. Students are also encouraged to read ST I, Q. 3, in its entirety, and can find more from Aquinas on this subject in Book I of his Summa Contra Gentiles, especially chapters 15-23.

Acknowledgements

The text from Aquinas has been taken from the Summa Theologiae, translated by the Fathers of the English Dominican Province, and made available for free online by The Aquinas Institute. This work is in the public domain. All images were created using Midjourney.

Citation

Kintz, James. 2025. “Keep It Simple: Thomas Aquinas’s Summa Theologiae Part I, Question 3.”  The Philosophy Teaching Library. Edited by Robert Weston Siscoe, <https://philolibrary.crc.nd.edu/article/keep-it-simple/>.

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By ‘science’, Plato means to be talking about all rational disciplines, including mathematics.

Key Concept

The form of the beautiful has to be perfectly beautiful because all instances of beautiful things are explained by it, so it has to be responsible for the highest possible degrees of beauty possessed by anything. Moreover, it has no trace of ugliness in it.

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The form of the beautiful has to be immaterial because all the many beautiful things do not share any material – that is, they are all made of different stuff.

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Form (εἶδος / ἰδέα) – Intelligible, immaterial, perfect entities that explain the unity among the many things which share the feature named by the entity (e.g., Beauty, Squareness, Oddness). For example, think of a square. There might be many different squares, but they all share features like having four sides of equal length. So, the Form of Squareness would include all of those features that make something a square.

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Guardian – This is the name Plato gives to the ruling class in his ideal city. Think of them as philosopher kings – they have complete control over the organization of the state. The Republic is partially about why Plato thinks they would be needed for an ideal system of government and what they would need to learn to do the job well.

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Plato has previously argued that we are made up of different parts. The first part is the appetitive which is responsible for our desires for food, sex, and other bodily needs. Then there is the spirited part, which longs for fame and honor. Finally, he identifies the rational part, which discerns what is good and bad for us through reason. The parts can all come into conflict with one another, and managing their relations is what Plato thinks justice is all about.

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Soul (ψῡχή) – What Greeks meant by this word is controversial. For now, think of it as the thing that makes you different from a rock or other objects, the thinking and experiencing part of you as well as the part of you that acts and makes decision. You might use the word ‘mind’ or ‘self’ to talk about this.

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Virtue – Virtues are the character traits that make a person good. For example, most people consider courage and generosity to be virtues. English-speakers usually reserve the word ‘virtue’ for human beings, but in ancient Greek the word can be more comfortably applied to other beings as well.

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Was it his burly physique, his wide breadth of wisdom, or his remarkable forehead which earned him this nickname?

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Aporia – A Greek term for “being at a loss” or “clueless.” Socrates often questions people until they have no idea how to define something that they thought they understood.

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You might be confused by the word ‘attention’ below. In Greek the word is therapeia, from which we get the English word ‘therapy.’ It primarily means the same as ‘service’ as in ‘to serve,’ but shades into ‘worship,’ ‘take care of,’ and ‘attend to.’

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Meletus – A poet and citizen of Athens and one of Socrates’ accusers. Amongst other things, Meletus accused Socrates of impiety and corrupting the youth.

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Divine Voluntarism – The idea that God is free to determine even the most basic truths. If divine voluntarism is true, then God could have made it so that 2+2=5 or so that cruelty and blasphemy are holy and good.

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Euthyphro Dilemma – The question, “Is a thing holy because the gods love it, or do the gods love it because it is holy?” The general idea of a forced choice (or “dilemma”) about the true order of explanation occurs often in philosophy and gets referred to by this term.

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Essence – What a thing fundamentally is. A square might be red or blue without changing the fact that it’s a square, but a square must have four sides, so having four sides is part of a square’s essence.

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Definition – The perfect description of a thing. A definition should pick out all and only examples of a thing. For example, ‘bachelor’ might be defined as ‘unmarried man,’ because all unmarried men are bachelors, and only unmarried men are bachelors.

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In Disney’s retelling of the Hunchback of Notre Dame, the clergyman Claude Frollo orders the death of many Roma on religious grounds. It is clear, however, that he is really motivated by spite and his unrequited lust for the Romani woman Esmerelda.

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Spanish conquistadors were shocked by the scope of ritual human sacrifice among the Aztecs, as hundreds or even thousands of people were sacrificed each year. The Aztecs thought that the sacrifices could repay the sacrifices the gods had made in creating the sun and earth.

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Zeus – The god of sky and thunder in ancient Greek mythology, Zeus was depicted as chief among the gods and called the father of the gods and men.

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Forms – The perfect, divine, and intelligible entities that exist independently of the physical world. They are comprehensible only through reason, not through our senses, and their existence explains the properties of objects in the physical world.

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Recollection – The soul existed prior to birth; during this time it learned everything, and hence all learning is only recalling what we already know.

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Immortality of the Soul – Unlike the body, the soul is not subject to physical death, because it is immortal and indestructible.

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Philosophy – The practice of preparing the soul for death by training it to think and exist independently of the body

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Death – Plato understands this as the soul’s separation from the body

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Human Identity Across Time – Locke’s notion that any human stays the same across time if, and only if, it maintains the same (distinctively human) organizing structure of parts.

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Substance Identity Across Time – Something is the same substance across a segment of time if, and only if, it continuously exists across the relevant segment of time without gaining or losing any of its parts.

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Immaterial Soul – A personal thinking substance without any physical constitution.

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Personal Identity Across Time – Whatever makes someone the numerically same person (i.e., that very person) at different times; according to Locke, it is a relation of first-person consciousness via memory.

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Person – Locke’s forensic definition of person (pertaining to courts of law regarding the justice of praise, blame, reward, or punishment): a thinking, intelligent being, that has reason and reflection, and can consider itself as itself, the same thinking thing in different times and places.

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The Prophet Muhammad is a central figure in Islam.  He is viewed as the last of a long line of prophets, which includes Moses and Jesus. He is responsible for writing the Quran, which was dedicated to him by the angel Gabriel.  His life and sayings are recounted in the Hadith; he is viewed as an exemplary role model of Islamic life and faith.

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Exhortation — The method of understanding and interpreting Truth available to the common people. The majority of people take scripture literally and understand truth and right action based upon this understanding. They are persuaded by the vivid imagery of the Quran and the rhetorical exhortations of religious leaders. Averroes takes this to be lowest form of understanding

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Dogmatic Discourse — The method of understanding displayed by those who, through natural ability and habit, are able to have a deeper understanding of the Quran, and of the truths it illuminates. These people know that not all of the scriptures are to be taken literally, and that greater underlying Truths are revealed by interpreting some elements allegorically. Still, they err on the side of dogmatism and literal interpretation whenever uncertainty arises. Averroes associates this way of thinking with Muslim theologians and views this to be the middle level of understanding.     

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Philosophical Inference – The type of understanding associated with philosophical demonstration or argument. This is the highest level of understanding, accomplished by a select few, who have a natural capacity for philosophy and proper philosophical training. 

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Law — The Quran (the central religious text of Islam) and, to a lesser extent, the Hadith (reports of what the prophet Muhammad said and did). Averroes is concerned with explaining how philosophy relates to what Muslims take to be the unerring Truth regarding God and the nature of existence, as they are expressed in Scripture.

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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.     

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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.

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Substance Dualism — a theory claiming that the mind (or soul) and body are two distinct and very different things.

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Body — what it sounds like! The body is the physical part or aspect of a thing and has characteristics like shape, size, etc.

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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.

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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.

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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.

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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.

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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.

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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.

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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.

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 Faith – Belief in and fidelity to a transcendent divine subject like God.

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Orthodoxy – Orthodoxy refers to “right belief,” and it is concern with identifying heresies and ensuring that people believe and practice correctly.

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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.

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Above the Individual Man – The human perfections are “above the individual” insofar as no particular individual ever perfectly realizes them. They are abstractions.

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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.

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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.

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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.

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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.

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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.

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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.

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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.

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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.

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Synthesis – The prefix ‘syn-’ means “together,” so a synthesis “brings together” or combines elements of both a thesis and its antithesis.

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Antithesis– An antithesis is the contradiction of a thesis. For example, internationalism could be understood as the antithesis of nationalism.

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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.

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Progressor’s Temptation – a unique temptation for those making progress in which pride impedes their further progress and leads to backsliding.

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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.

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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.

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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.

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Askeses – exercises of Stoic thought and practice that make the lessons and habits of Stoic philosophy second-nature for Stoic practitioners.

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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. 

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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.

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The Greatest Happiness Principle – A principle which says that actions are right insofar as they promote happiness and wrong insofar as they promote unhappiness

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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.

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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.

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Utilitarianism – A normative theory of which actions are right or wrong. Utilitarianism says the right action is that which maximises utility.

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Jeremy Bentham – Considered by some as the father of utilitarianism, Bentham was a moral philosopher and one of John Stuart Mill’s teachers

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Epicurus – an ancient Greek philosopher and one of the first to advocate that the ultimate good is experiencing pleasure and avoiding pain.

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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.

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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)

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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.

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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.

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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. 

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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.

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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. 

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Contingent Being – A being that can fail to exist. Its existence is not guaranteed. This being might come to exist or it might not.

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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.

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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.

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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.

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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.

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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. 

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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. 

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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.

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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.

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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.

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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.

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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.

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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.

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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. 

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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.

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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.” 

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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.

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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. 

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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.  

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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.’

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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. 

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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.

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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.

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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.

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Doxastic Voluntarism – the view that we have at least some control over what we believe.

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Evidence – information that increases the probability that a claim is true.

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Sufficient – enough of something for a particular purpose. Whether something is sufficient is context-dependent.

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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

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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

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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

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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.”

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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

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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

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Final Good – A good that we pursue for its own sake. Common examples of final goods include happiness, knowledge, and friendship

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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

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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

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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

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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

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Meletus – A poet and citizen of Athens and one of Socrates’ accusers. Amongst other things, Meletus accused Socrates of corrupting the youth

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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

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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

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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

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Philosophical Skepticism – The position that we do not know many things that we ordinarily take ourselves to know

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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

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A Priori Knowledge – Knowledge that can be gained without having any particular concrete experiences. Such knowledge is typically gained by rational insight or intuition

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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

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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.

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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.

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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.

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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.

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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

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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

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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.

Historical Connection

Solon’s Warning

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

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Historical Connection

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

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