Doubt Everything
René Descartes' Meditations on First Philosophy, Meditation 1

Picture of <b>Wes Siscoe</b><br><small>Assistant Professor of Philosophy, Bowling Green State University</small>
Wes Siscoe
Assistant Professor of Philosophy, Bowling Green State University

Table of Contents

Warm-Up: Is it Possible We are All in the Matrix?

In the science fiction movie The Matrix, Morpheus asks Neo a simple question: Will he take the blue pill or the red pill? If he takes the blue pill, he will go on with his life and forget that he ever met Morpheus. If he takes the red pill, he will learn what the world is really like. As Morpheus says, “All I am offering is the truth, nothing more.”

Neo takes the [Spoiler Alert!] red pill, forever changing his understanding of reality. As it turns out, the world is actually ruled by machines imbued with artificial intelligence. Neo’s actual body is connected to a vast power grid, and his mind has been connected, not to the real world, but to the simulated reality of the Matrix. 

Now this is all pretty far-fetched. From chess-playing computers like Deep Blue to large language models like ChatGPT, computer scientists have made a lot of progress when it comes to artificial intelligence. But we are still far from a place where artificial intelligence could take over and trap us in an entirely simulated world.

At the same time, isn’t it possible that we are in the Matrix? That artificial intelligence has actually already been developed, and that it is now creating the illusion that we are just discovering it? What evidence do you have to rule this out? 

In today’s reading, we will critically examine Descartes’ arguments that reality is not what it appears to be. Even though Descartes wasn’t thinking about the Matrix, he still made the case that we might all be dreaming, or that we might all be deceived by an evil demon. Is there any way that we can rule these things out?

Introduction

René Descartes (1596-1650) was a French mathematician and philosopher and is considered the father of modern philosophy. Coinciding with a period of scientific exploration and discovery in Europe, modern philosophy emphasized the use of reason over a dependence on traditional ways of thinking about the world. Embodying this spirit, Descartes split with many of the medieval and scholastic philosophers that came before him and attempted to build a philosophical system from scratch. In his Meditations on First Philosophy, Descartes begins this project by considering how much we can know about the world around us. 

Descartes splits his meditations up into six parts. In this first meditation, which will be the topic of this reading, he begins by considering which of our beliefs we should be certain about and which we have some reason to doubt. If you’re interested, the full text of all six of Descartes’ Meditations can be found here.

Key Concepts

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

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

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

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

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

The Method of Doubt

Descartes begins his investigation by explaining the project he is embarking on and laying out the method he will use to reach his conclusions.

Meditation 1, Paragraphs 1-2

Several years have now elapsed since I first became aware that I had accepted, even from my youth, many false opinions for true, and that consequently what I afterward based on such principles was highly doubtful; and from that time I was convinced of the necessity of undertaking once in my life to rid myself of all the opinions I had adopted, and of commencing anew the work of building from the foundation, if I desired to establish a firm and abiding superstructure in the sciences. But as this enterprise appeared to me to be one of great magnitude, I waited until I had attained an age so mature as to leave me no hope that at any stage of life more advanced I should be better able to execute my design.

But, to this end, it will not be necessary for me to show that the whole of [my former opinions] are false—a point, perhaps, which I shall never reach; but as even now my reason convinces me that I ought not the less carefully to withhold belief from what is not entirely certain and indubitable, than from what is manifestly false, it will be sufficient to justify the rejection of the whole if I shall find in each some ground for doubt. Nor for this purpose will it be necessary even to deal with each belief individually, which would be truly an endless labor; but, as the removal from below of the foundation necessarily involves the downfall of the whole edifice, I will at once approach the criticism of the principles on which all my former beliefs rested.

In this passage, Descartes explains that he wants to establish a firm foundation for the sciences. Descartes disagreed with many of the scientists that came before him, particularly in how they were inspired by certain Aristotelian philosophy, and so his project was to create a basis for science that was not vulnerable to such errors. In order to do this, Descartes employs the Cartesian Method of Doubt. Following this method, Descartes doubts all of his beliefs that there is a chance he could be wrong about, even if that chance seems very remote and far-fetched.

Video

Check out this video to hear the Cartesian Method of Doubt explained by a philosophy professor:

Can I Trust My Senses?

Having laid out his project, Descartes begins by applying his method. As he says in the previous passage, he does not plan on considering all his beliefs one-by-one. Instead, he focuses on the sources of his previous beliefs, allowing him to consider a whole category of his beliefs at the same time. The first source that Descartes examines are his senses. Is there anything he has learned through his sight, touch, taste, or smell which he can be certain about?

Meditation 1, Paragraphs 3-4

All that I have, up to this moment, accepted as possessed of the highest truth and certainty, I received either from or through the senses. I observed, however, that these sometimes misled us; and it is the part of prudence not to place absolute confidence in that by which we have even once been deceived.

But it may be said, perhaps, that, although the senses occasionally mislead us respecting minute objects, and such as are so far removed from us as to be beyond the reach of close observation, there are yet many other of their informations (presentations), of the truth of which it is manifestly impossible to doubt; as for example, that I am in this place, seated by the fire, clothed in a winter dressing gown, that I hold in my hands this piece of paper, with other intimations of the same nature. But how could I deny that I possess these hands and this body, and withal escape being classed with persons in a state of insanity, whose brains are so disordered and clouded by dark bilious vapors as to cause them pertinaciously to assert that they are monarchs when they are in the greatest poverty; or clothed [in gold] and purple when destitute of any covering; or that their head is made of clay, their body of glass, or that they are gourds? I should certainly be not less insane than they, were I to regulate my procedure according to examples so extravagant.

Do It Yourself!

When Have Your Senses Deceived You?
Descartes points out that there are occasions where his senses have deceived him. We have all experienced how a stick looks bent when it is half underwater, and how the road ahead can appear wet on a hot summer day. If we are following the Cartesian Method of Doubt, then because our senses have misled us, then we should kick to the curb all of our beliefs that are supplied by our senses. Can you think of any more examples? What is another way that our senses lead us astray?

Am I Dreaming?

At first, Descartes finds it almost unthinkable that he could doubt his senses. But then he considers the possibility that what he is experiencing isn’t actually produced by his senses at all, but is rather part of some elaborate dream. If this is true, he might not be able to trust his experiences after all…

Meditation 1, Paragraph 5

Though this be true, I must nevertheless here consider that I am a man, and that, consequently, I am in the habit of sleeping, and representing to myself in dreams those same things, or even sometimes others less probable, which the insane think are presented to them in their waking moments. How often have I dreamt that I was in these familiar circumstances, that I was dressed, and occupied this place by the fire, when I was lying undressed in bed? At the present moment, however, I certainly look upon this paper with eyes wide awake; the head which I now move is not asleep; I extend this hand consciously and with express purpose, and I perceive it; the occurrences in sleep are not so distinct as all this. But I cannot forget that, at other times I have been deceived in sleep by similar illusions; and, attentively considering those cases, I perceive so clearly that there exist no certain marks by which the state of waking can ever be distinguished from sleep, that I feel greatly astonished; and in amazement I almost persuade myself that I am now dreaming.

Thought Experiment

Can I Tell When I’m Dreaming?
In this passage, Descartes entertains the possibility that everything he is currently experiencing is a dream. His nightgown, his chair by the fire, all of it. Descartes’ key insight is that, if he cannot tell the difference between dreaming and being awake, then he has some reason to doubt the experiences that seem to come from his senses. So that’s the question. Can you tell when you are awake and when you are dreaming? Are there any obvious indicators that give your dreams away? I have had dreams that were so strange that, right in the middle of them, I became convinced that I was dreaming. So maybe it is possible to tell when we’re dreaming. What do you think? Can you tell the difference between when you’re dreaming and when you’re awake?

Physics, Arithmetic, Geometry, Oh My!

If Descartes is right and we can’t distinguish when we are dreaming from when we are awake, what does this mean for our sensory experiences? Should we doubt everything that we learn from our senses? Another issue is how these reflections apply to different areas of study, subjects like physics, arithmetic, and geometry. Can we trust what we learn about these subject matters?

Meditation 1, Paragraphs 6, 8

Let us suppose, then, that we are dreaming, and that all these particulars—namely, the opening of the eyes, the motion of the head, the forth-putting of the hands—are merely illusions; and even that we really possess neither an entire body nor hands such as we see. Nevertheless it must be admitted at least that the objects which appear to us in sleep are, as it were, painted representations which could not have been formed unless in the likeness of realities; and, therefore, that those general objects, at all events, namely, eyes, a head, hands, and an entire body, are not simply imaginary, but really existent. For, in truth, painters themselves, even when they study to represent sirens and satyrs by forms the most fantastic and extraordinary, cannot bestow upon them natures absolutely new, but can only make a certain medley of the members of different animals; or if they chance to imagine something so novel that nothing at all similar has ever been seen before, and such as is, therefore, purely fictitious and absolutely false, it is at least certain that the colors of which this is composed are real. And on the same principle, although these general objects, viz. [a body], eyes, a head, hands, and the like, be imaginary, we are nevertheless absolutely necessitated to admit the reality at least of some other objects still more simple and universal than these, of which, just as of certain real colors, all those images of things, whether true and real, or false and fantastic, that are found in our consciousness, are formed.

We will not, therefore, perhaps reason illegitimately if we conclude from this that Physics, Astronomy, Medicine, and all the other sciences that have for their end the consideration of composite objects, are indeed of a doubtful character; but that Arithmetic, Geometry, and the other sciences of the same class, which regard merely the simplest and most general objects, and scarcely inquire whether or not these are really existent, contain somewhat that is certain and indubitable: for whether I am awake or dreaming, it remains true that two and three make five, and that a square has but four sides; nor does it seem possible that truths so apparent can ever fall under a suspicion of falsity [or incertitude].

Connection

A Priori and A Posteriori Knowledge

Even though Descartes concludes that he cannot trust his senses, that doesn’t mean that we have to throw out everything we believe about the world. In particular, he thinks that we can hold onto our a priori knowledge. A Priori Knowledge can be learned just by thinking. Consider Descartes’ example that 2+3=5. This isn’t something we can only learn by experiencing the world. If I know that I have a carton of 2 apples on the counter and 3 in the refrigerator, I do not need to check and see whether I have 5 apples. I know that 2+3 is always equal to 5, and so Descartes thinks that I do not need to doubt that this is true even when I am dreaming and deceived about my sensory experiences. Among the subjects that can be learned a priori, Descartes includes arithmetic and geometry.

A Posteriori Knowledge, on the other hand, is vulnerable to misleading dreams. A posteriori knowledge can only be gained by learning about the real world, and so if our senses lead us astray, this can prevent us from learning what the world is like. Some examples of things that have been discovered a posteriori include the strength of gravity or that water boils at 100° Celsius. These are not truths that we can arrive at only by thinking, and we only learned about them through scientific discoveries about the way the world works. If we’re dreaming though, all bets are off!

An Omnipotent… Evil Demon?

So far, Descartes has entertained a form of Philosophical Skepticism, doubting that he knows many things which we ordinarily take ourselves to know. But philosophical skepticism can come in stronger or weaker forms. Descartes started out by doubting some of the things which he learned via his senses, and then used the dreaming argument to doubt that he knows anything except certain a priori propositions. In this passage, we’ll see that Descartes thinks that there is reason to doubt even 2+3=5 right alongside scientific claims like water boiling at 100° Celsius.

Meditation 1, Paragraphs 9, 12

Nevertheless, the belief that there is a God who is all powerful, and who created me, such as I am, has, for a long time, obtained steady possession of my mind. How, then, do I know that he has not arranged that there should be neither earth, nor sky, nor any extended thing, nor figure, nor magnitude, nor place, providing at the same time, however, for [the rise in me of the perceptions of all these objects, and] the persuasion that these do not exist otherwise than as I perceive them? And further, as I sometimes think that others are in error respecting matters of which they believe themselves to possess a perfect knowledge, how do I know that I am not also deceived each time I add together two and three, or number the sides of a square, or form some judgment still more simple, if more simple indeed can be imagined? But perhaps Deity has not been willing that I should be thus deceived, for he is said to be supremely good.

I will suppose, then, not that Deity, who is sovereignly good and the fountain of truth, but that some malignant demon, who is at once exceedingly potent and deceitful, has employed all his artifice to deceive me; I will suppose that the sky, the air, the earth, colors, figures, sounds, and all external things, are nothing better than the illusions of dreams, by means of which this being has laid snares for my credulity; I will consider myself as without hands, eyes, flesh, blood, or any of the senses, and as falsely believing that I am possessed of these; I will continue resolutely fixed in this belief, and if indeed by this means it be not in my power to arrive at the knowledge of truth, I shall at least do what is in my power, viz., [suspend my judgment], and guard with settled purpose against giving my assent to what is false, and being imposed upon by this deceiver, whatever be his power and artifice. But this undertaking is arduous, and a certain indolence insensibly leads me back to my ordinary course of life; and just as the captive, who, perchance, was enjoying in his dreams an imaginary liberty, when he begins to suspect that it is but a vision, dreads awakening, and conspires with the agreeable illusions that the deception may be prolonged; so I, of my own accord, fall back into the train of my former beliefs, and fear to arouse myself from my slumber, lest the time of laborious wakefulness that would succeed this quiet rest, in place of bringing any light of day, should prove inadequate to dispel the darkness that will arise from the difficulties that have now been raised.

Argument

The Evil Demon

In this passage, Descartes imagines a demon powerful enough to deceive him about everything he believes (there is actually one key belief that he thinks he can be certain about, but we’ll have to save that for his second Meditation!), giving him at least a small reason to doubt all that he thinks is true. If we lay out The Evil Demon Argument using premises and a conclusion, it would look something like this:

Premise 1: It is possible that I could be deceived by a powerful demon about everything I believe

Premise 2: If it is possible that I could be deceived by a powerful demon about everything I believe, then I cannot be certain about anything that I believe

Conclusion: I cannot be certain about anything that I believe

Descartes motivates the first premise by imagining a demon so powerful that it could deceive him at will, creating vast and complex illusions. In this case, the demon might even be capable of deceiving him about basic arithmetic, so strong would the illusions be. But, as we see with the connection drawn by the second premise, if such a demon does exist, then we cannot be certain about anything that we believe. While it might only provide us with a very small reason to doubt that the reality is as we take it to be, that can still provide us with a small reason for not being absolutely certain.

Summary

In Descartes’ First Meditation, we saw that he wanted to establish a certain foundation for his beliefs. In order to do that, he rejected all beliefs that he had at least some reason to doubt. By considering the possibility that he might be dreaming, he came to think that his senses could not be fully trusted, and the possibility of deception by a very powerful evil demon gave him reason to think that even things he thought he knew a priori, like his mathematical beliefs, could be mistaken. In his Second Meditation, Descartes picks up where we left off, considering whether he has any certain beliefs.

Connection

The Brain-in-a-Vat

Are there any other arguments that can give us reason to doubt everything we believe? In our Warm-Up, we considered a world like the one depicted in the Matrix, where the experiences of most people are of a very sophisticated virtual simulation. If we think that this is a possibility that we can’t rule out, then we could create our own version of Descartes’ argument, starting with the premise that it is possible we are being deceived by very sophisticated artificial intelligence.

In fact, many contemporary philosophers use a different thought experiment than Descartes’ Evil Demon. In its place, they discuss whether we can know that we are not a brain in a vat. The example is discussed so often in philosophy, that there is now even an entire book focused on the thought experiment titled The Brain in a Vat! In many cases where this example is used, the imagined brain is kept alive and hooked up to a simulation by a mad scientist, but it could just as easily be controlled by advanced AI, just like we find in the Matrix.

Want to Learn More?

If you’re curious where Descartes’ method of doubt ultimately takes him, pick up the story with his Second Meditation, where he lands on a conclusion of which he can be certain. And for an overview of how contemporary philosophers think about skepticism, see the articles “Contemporary Skepticism” and “The Brain in a Vat Argument” on the Internet Encyclopedia of Philosophy.

Acknowledgements

This work has been adapted from Meditations on First Philosophy, a title from the eCampusOntario Public Domain Core Collection. This work is in the Public Domain. All images were created using Midjourney and are the property of the Philosophy Teaching Library.

Citation

Siscoe, Robert Weston. 2023. “Doubt Everything: Rene Descartes’ Meditations on First Philosophy, Meditation 1.” The Philosophy Teaching Library. Edited by Robert Weston Siscoe, <https://philolibrary.crc.nd.edu/article/doubt-everything/>.

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Key Concept

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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