SLIDE 1: Title Slide
Okay, so here’s a question that’s probably crossed your mind at some point: What if everything you’re absolutely certain about… is wrong?
Not just a little wrong. Not “oops, I misread the data” wrong. But fundamentally, completely, can’t-even-know-if-you’re-wrong wrong.
Now, most philosophers throughout history have heard that question and responded with something like: “Well, that’s terrifying, so let me spend the next 500 pages proving why I’m definitely right about everything.”
But there was this guy—a physician, actually, living in the Roman Empire around 200 CE—who heard that question and thought: “You know what? That sounds… peaceful.”
His name was Sextus Empiricus, and today we’re diving into one of the most counterintuitive philosophical positions ever developed: the idea that doubt itself might be the path to inner tranquility.
Welcome to the ancient art of not being sure about anything—and why that might be exactly what you need.
SLIDE 2: The Man Behind the Method
So let’s start with the man himself, because Sextus is one of those historical figures where we know just enough to be frustrated by how little we actually know.
Here’s what we’ve got: Sextus Empiricus—and yes, that’s a Latin name, which tells us he was probably a Roman citizen—lived and worked sometime around 160 to 210 CE. We’re not entirely sure where he was born, but he likely taught in one of the major intellectual centers of the ancient world: Alexandria, Rome, or Athens.
And here’s where it gets interesting—he wasn’t primarily a philosopher. He was a physician. Specifically, he belonged to what was called the Empiric school of medicine.
Now, the Empirics had this radical idea: instead of developing grand theories about how the body works based on abstract principles—you know, “the four humors” and all that—they said, “Let’s just observe what actually happens. Let’s see what treatments work, and let’s not pretend we know why they work.”
Experience over theory. Observation over speculation.
Sound familiar? Because that same instinct—that same skepticism about grand theoretical claims—is exactly what Sextus brought to philosophy.
But here’s the thing that makes Sextus absolutely crucial: he wrote the most comprehensive account of Pyrrhonian scepticism that survived from the ancient world. His major work, the Outlines of Pyrrhonism, is basically our only detailed window into this entire philosophical tradition.
Without Sextus, we might have lost this way of thinking entirely.
And there’s this beautiful irony here that I want you to catch: Sextus was a doctor—someone whose job was to heal people, to relieve suffering. But instead of prescribing herbs or bloodletting or whatever the medical fashion of the day was, he prescribed doubt.
He looked at human mental suffering—anxiety, dogmatism, the endless conflicts that arise when people are absolutely convinced they’re right—and he thought: “What if the cure isn’t finding the right answers? What if the cure is learning to live without needing them?”
Which brings us to the key question we’re going to explore today…
“What if the cure for mental suffering isn’t finding the right answers, but learning to live without them?”
Now, before you think this is just ancient navel-gazing, let me tell you—this question is shockingly relevant today. We live in an age of absolute certainty. Everyone’s convinced they’re right. Political tribalism, online arguments, conspiracy theories, ideological echo chambers…
What if a 2nd-century Roman physician had already figured out the antidote?
Let’s find out.
SLIDE 3: Three Paths to Truth
How Do We Respond to the Search for Truth?
Sextus identified three distinct philosophical approaches:
1. The Dogmatists (Aristotle, the Stoics)
– Claim: “We have discovered the truth!”
– Possess certain knowledge of reality
– Build entire systems on foundational certainties
2. The Academic Sceptics (Plato’s later followers)
– Claim: “Truth is unknowable!”
– Deny the possibility of certain knowledge
– Assert that we cannot know
3. The Pyrrhonian Sceptics (Sextus’ approach)
– Claim: “We’re still investigating…”
– Suspend judgement on all dogmatic claims
– Avoid both assertion and denial
The Crucial Difference: Pyrrhonians don’t claim to know that nothing can be known. They simply… keep looking.
SLIDE 4: The Art of Suspension (Epoché)
Epoché (ἐποχή): The suspension of judgement
How It Works:
Step 1: Examine opposing arguments on any question
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Step 2: Find them equally strong/weak
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Step 3: Recognize equal probability on both sides
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Step 4: Naturally stop affirming or denying
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Result: Ataraxia (ἀταραξία) – Inner peace and tranquility
The Paradox: Freedom comes not from finding truth, but from releasing the need to grasp it.
Alright, so Sextus looked around at the philosophical landscape of his time—and honestly, it wasn’t that different from today—and he noticed something fascinating. When it comes to the fundamental question of truth and knowledge, people basically fall into three camps.
Let’s break these down, because understanding these distinctions is absolutely crucial.
First, you’ve got the Dogmatists. Now, this includes some heavy hitters—Aristotle, the Stoics, basically anyone who walks around saying, “I’ve figured it out. I know how reality works.”
These are the philosophers who build massive systematic theories. They’ll tell you about the nature of the soul, the structure of the cosmos, the foundation of ethics, the ultimate purpose of human life—and they’ll do it with certainty.
“The good life consists in virtue.” “The universe operates according to rational principles.” “Knowledge comes from sense perception properly understood.”
And look, I’m not saying these people were stupid. Far from it. Some of the most brilliant minds in human history were dogmatists. But Sextus noticed something: they all disagreed with each other. Profoundly. Fundamentally.
If everyone’s so certain, and everyone’s certain about different things… what does that tell you?
Then you’ve got the Academic Sceptics—these were followers of Plato’s Academy who took a different route. They looked at all this disagreement and said, “You know what? Truth is unknowable. We can’t have certain knowledge. Period.”
Now, this sounds similar to what Sextus is doing, right? But here’s where it gets weird—and this is crucial—the Academic Sceptics are making a dogmatic claim about knowledge.
They’re saying they know that you can’t know.
You see the problem? They’ve just smuggled certainty back in through the back door. They’re absolutely certain that absolute certainty is impossible.
It’s like saying, “I’m positive that you can’t be positive about anything.” The statement defeats itself.
Which brings us to Sextus and the Pyrrhonians—and this is where it gets really interesting.
The Pyrrhonian doesn’t say “I know the truth.” But they also don’t say “Truth is unknowable.”
They say… “I’m still looking. I’m still investigating. And right now, I’m not making any definitive claims either way.”
It’s not nihilism. It’s not giving up. It’s something much more subtle and, honestly, much more difficult to maintain.
“We’re still investigating…”
Think about what that means. Every time someone demands you take a position—”Do you believe in free will or determinism?” “Is there objective morality or isn’t there?” “Does God exist or not?”—the Pyrrhonian response is: “Show me the arguments on both sides, and I’ll tell you if either one is convincing enough to warrant certainty.”
Spoiler alert: they never are.
So how does this actually work in practice? This is where we get to one of the most important concepts in Sextus’ philosophy: epoché.
Eh-po-KAY. It’s Greek for “suspension” or “holding back.”
And it’s not some mystical meditation technique. It’s actually a pretty straightforward intellectual process. Let me walk you through it.
Step one: You examine opposing arguments on any question. Let’s say… “Is the soul immortal?”
Step two: You find that the arguments on both sides are equally strong. Or equally weak, depending on how you look at it. The point is, they balance out.
Step three: You recognize that there’s equal probability—or equal improbability—on both sides. You genuinely can’t tell which position has better support.
Step four: And here’s the key—you naturally stop affirming or denying. Not because you’re forcing yourself, but because… well, what else can you do? If the arguments are genuinely balanced, making a definitive claim would be arbitrary.
And then—this is what Sextus discovered—something unexpected happens.
Ataraxia. Inner peace. Tranquility.
Now, this is the part that blew my mind when I first really understood it. Sextus isn’t saying, “Suspend judgement because it’s intellectually honest” or “because it’s the logically correct position.”
He’s saying: Try it and see what happens to your mental state.
Think about the last time you were in a heated argument—political, religious, whatever. Think about how it felt. The anxiety. The need to be right. The mental energy spent defending your position, attacking the other side, lying awake at night thinking of better arguments you should have made…
All that suffering comes from attachment to belief. From clinging to certainty about things that might not be certain at all.
And here’s the paradox that Sextus discovered—the beautiful, counterintuitive paradox at the heart of Pyrrhonian scepticism:
“Freedom comes not from finding truth, but from releasing the need to grasp it.”
When you stop needing to be right, when you genuinely suspend judgement on questions where the evidence is balanced… you stop suffering about them.
Not because you’ve given up. Not because you don’t care. But because you’ve recognized that clinging to unverifiable beliefs causes more pain than it relieves.
Now, I know what some of you are thinking: “But Professor Leshley, doesn’t this lead to paralysis? If I suspend judgement on everything, how do I make decisions? How do I live?”
Excellent question. And Sextus has an answer. But before we get there, we need to understand his method—the actual tools he used to achieve this suspension of judgement.
Because it’s not enough to just say “I’m going to suspend judgement.” You need a systematic way of examining arguments, of finding that balance point where certainty becomes impossible.
And that’s exactly what we’re going to explore next: Sextus’ famous Ten Modes—the toolkit for cultivating doubt.
Slide 5
Okay, so now we get to the really fun part. The how of Pyrrhonian scepticism.
Because it’s one thing to say “suspend judgement.” It’s another thing entirely to actually do it when you’re confronted with arguments that seem convincing, or when your own perceptions seem obviously true, or when everyone around you is absolutely certain about something.
Enter the Ten Modes—and these are brilliant. Absolutely brilliant.
Now, Sextus didn’t invent these. He inherited them from an earlier Pyrrhonian named Aenesidemus, who lived a couple centuries before him. But Sextus refined them, systematized them, and turned them into a genuine philosophical toolkit.
Think of these as ten different strategies for showing that any claim to certain knowledge can be challenged. Ten ways of demonstrating that for every argument, there’s a counter-argument of equal strength.
Let’s go through them—and I want you to notice something as we do: how practical these are. How they apply to everyday life, not just abstract philosophical debates.
First mode: Different animals perceive the world differently.
Okay, simple example. A dog experiences the world primarily through smell. Their olfactory reality is so rich, so detailed, that we can barely imagine it. Meanwhile, we’re visual creatures—we navigate by sight in ways that would be completely alien to a bat using echolocation.
So here’s the question: When you look at a rose and see red petals, and a bee looks at the same rose and sees ultraviolet patterns we can’t even perceive… which one of you is seeing the rose as it “really” is?
The dogmatic philosopher says, “Well, obviously we are. Human perception is the standard.” But why? What makes human perception privileged? What makes your sensory apparatus the one that reveals objective reality?
You see the problem. Once you start asking that question, certainty starts to slip away.
Mode 2: Variability Among Humans
Second mode: Even among humans, we perceive and judge things differently.
Think about taste. Some people love cilantro; others think it tastes like soap—and that’s actually genetic, by the way. Some people are colorblind. Some have perfect pitch. Some are supertasters with more taste buds than average.
But it goes deeper than just physiology. Cultural background, personal history, psychological state—all of this shapes how we experience and interpret the world.
So when two people have a fundamental disagreement—about morality, about politics, about what’s beautiful or disgusting or sacred—how do you determine who’s right? What’s your standard? Your own perception? Why is yours more valid than theirs?
Mode 3: Different Sense Organs
Third mode: Our different senses give us conflicting information about the same object.
Classic example from Sextus: Honey tastes sweet, but it looks yellow. Which property is more “real”—its sweetness or its yellowness?
“Well, both,” you might say. But here’s the thing—you’re already making a judgement about how to reconcile conflicting sensory data. You’re interpreting. You’re not just passively receiving objective truth.
And if you’re interpreting, you could be interpreting wrong.
Mode 4: Circumstances & Conditions
Fourth mode: The same object appears different under different circumstances.
Wine tastes different when you’re sick versus when you’re healthy. Colors look different in daylight versus candlelight. Sounds are different when you’re moving versus standing still. Your judgement of temperature depends on whether you just came in from the cold or the heat.
So which perception is the true one? The one when you’re healthy? Why? Because that’s “normal”? But who decides what counts as the normal, standard condition for perceiving reality?
You’re starting to see the pattern, right?
Mode 5: Positions, Distances, Locations
Fifth mode: Perspective matters. Where you’re standing changes what you see.
A tower looks round from a distance, square up close. The same painting looks different from different angles. The oar in water looks bent; out of water, straight.
And here’s what Sextus is getting at: There’s no privileged vantage point. No cosmic perspective from which you can say, “This is how things really are, independent of any observer’s position.”
You’re always observing from somewhere. And that somewhere shapes what you observe.
Alright, five down, five to go. And these next ones get even more interesting because they start to move beyond just perception into judgement, culture, and meaning.
Mode 6: Admixtures
Sixth mode: We never perceive anything in isolation. Everything comes to us mixed with something else.
You don’t see “pure” color—you see color on a surface, in a context, surrounded by other colors. You don’t taste “pure” flavor—you taste food mixed with saliva, affected by temperature, influenced by smell.
So when you claim to know what something is, you’re really only knowing how it appears when mixed with all these other factors. You’ve never encountered the “thing in itself.”
Kant’s going to make a whole philosophy out of this idea 1,500 years later, but Sextus already saw it.
Mode 7: Quantities & Compositions
Seventh mode: The amount and arrangement of something changes its properties.
A single grain of sand? Harmless. A beach full of sand? You can drown in it. One glass of wine? Pleasant. A whole barrel consumed at once? Fatal.
Shavings of a goat’s horn look white; the whole horn looks black. So what color is the horn, really?
The point is: properties aren’t just “in” the object. They emerge from quantity, from arrangement, from context.
Mode 8: Relativity
Eighth mode: Everything we know is known in relation to something else.
This is huge. This is maybe the most important mode.
We say something is “large”—but large compared to what? We say it’s “good”—good for whom, in what circumstances? We say it’s “moving”—moving relative to what reference frame?
Sextus’ point is that we never grasp things “in themselves,” absolutely, independent of any relation. All our knowledge is relational. All our judgements are comparative.
And if that’s true—if we can only ever know things in relation to other things, which we also only know in relation to other things—then we’re caught in this infinite web of relations with no absolute foundation.
No bedrock. No certainty.
Mode 9: Frequency of Occurrence
Ninth mode: Familiarity and rarity change our judgements.
The sun rises every day—we barely notice it. But a solar eclipse? Everyone stops and stares. Same celestial mechanics, different reaction.
Or think about this: If you’d never seen a human being before, and someone showed you one, you’d think it was the weirdest, most improbable creature imaginable. Bilateral symmetry! Opposable thumbs! The ability to make complex sounds! But because you see humans all the time, you think they’re normal.
So our sense of what’s normal, what’s remarkable, what’s worthy of explanation—all of that depends on how often we encounter it. Not on any objective property of the thing itself.
Mode 10: Customs, Laws, Beliefs
Tenth mode: Different cultures have radically different beliefs about what’s true, what’s moral, what’s sacred.
The Persians thought it was pious to marry your sister. The Greeks thought that was abhorrent. Some cultures bury their dead; others burn them; others leave them for birds. Who’s right?
And this isn’t just ancient history. Today, we have fundamental disagreements across cultures about gender roles, about individual rights versus collective responsibility, about what counts as justice, about the relationship between humans and nature…
So when someone claims their moral beliefs are objectively true, Sextus asks: How do you know? How do you prove that your culture’s values are the correct ones and everyone else is wrong?
You can’t. Not without already assuming what you’re trying to prove.
Okay, so let’s zoom out for a second and see what Sextus has done here.
These ten modes aren’t just random observations. They’re a system. A method. And the pattern is always the same:
“Every claim about reality can be countered with an equally plausible opposing view.”
Not a better view. Not a worse view. An equally plausible view.
That’s the key. Sextus isn’t trying to prove that your beliefs are wrong. He’s showing that for any belief you hold with certainty, there’s a counter-belief that’s just as well-supported by the evidence.
And when you genuinely see that—when you really grasp that the arguments balance out—you can’t help but suspend judgement.
“The result: Justified suspension of judgement—epoché.”
Not because you’re intellectually lazy. Not because you don’t care about truth. But because you’re being honest about the limits of what you can actually know with certainty.
And that honesty—that intellectual humility—is the first step toward the tranquility Sextus promises.
But here’s where it gets really interesting. Because now we have to ask: If Sextus is right, if we really should suspend judgement on all these fundamental questions… doesn’t that create some serious problems?
I mean, how do you reason at all? How do you make arguments? How do you justify anything—including scepticism itself?
Sextus saw these objections coming. And his responses are… well, they’re either brilliant or deeply frustrating, depending on your perspective.
Let’s find out which.
Slides 7
Alright, so we’ve seen Sextus’ toolkit—the Ten Modes that systematically undermine our confidence in dogmatic claims. But now we need to go deeper.
Because Sextus wasn’t just interested in showing that our perceptions are unreliable. He wanted to show that the very foundations of knowledge—the bedrock that philosophers thought they could build on—are fundamentally unstable.
And he identified three devastating problems that any attempt to establish certain knowledge has to face.
These are… these are genuinely difficult. Even today, 1,800 years later, philosophers are still wrestling with these issues.
Problem 1: The Infinite Regress
Okay, imagine you make a claim: “I know X is true.”
I ask you: “How do you know?”
You say: “Because of criterion A.”
But now I ask: “How do you know criterion A is valid? How do you know it’s a good way of determining truth?”
So you appeal to criterion B to validate criterion A. But then I ask about criterion B. And you need criterion C. And then criterion D…
Where does it stop?
At some point, you have to just assert that one of your criteria is valid without being able to prove it. You have to make an arbitrary stopping point. You have to say, “This is just self-evidently true, and I’m not going to justify it further.”
But that’s dogmatism. That’s assuming what you’re trying to prove.
And here’s what’s devastating about this: It applies to everything. Logic? You need a criterion to validate logical principles. Sense perception? You need a criterion to validate that senses are reliable. Reason itself? You need a criterion to validate that reason works.
It’s criteria all the way down. And at the bottom? Nothing solid. Just an arbitrary decision to stop asking questions.
Problem 2: Circular Reasoning
Or—or—you try to avoid the infinite regress by going in a circle.
Classic example: “How do I know the Bible is true? Because the Bible says it’s the word of God. How do I know the Bible is the word of God? Because the Bible is true.”
You see the problem. You’re using the thing you’re trying to validate as the validator.
But this isn’t just a problem for religious fundamentalists. It’s a problem for any foundational claim.
“How do I know reason is reliable? Because reason tells me it is.”
“How do I know my senses give me accurate information? Because my senses tell me they do.”
It’s like asking a pathological liar, “Are you lying right now?” and accepting their answer as definitive proof.
Sextus’ point: You can’t use a criterion to validate itself. That’s not justification—that’s just assertion with extra steps.
Problem 3: The Problem of Induction
And then—then—we get to what might be Sextus’ most profound insight. And it’s wild that he saw this in the 2nd century, because it wouldn’t become a major philosophical problem until David Hume raised it again in the 18th century.
The problem of induction.
Here’s how it works: We observe particular cases—the sun rose yesterday, the sun rose today, the sun rose the day before that—and we generalize to a universal law: “The sun always rises.”
But how do we know that’s true? How do we know the future will resemble the past?
“Well, because it always has!” you say. “Every time we’ve checked, the future did resemble the past, so we can be confident it will continue to do so.”
But wait. You just used induction to justify induction.
You observed that induction has worked in the past, and you’re using that observation to conclude that induction will work in the future. You’re assuming the very thing you’re trying to prove.
It’s circular reasoning all over again.
And this isn’t some abstract philosophical game. This is about everything we claim to know scientifically. Every natural law. Every prediction. Every generalization from observed cases to unobserved ones.
We can’t prove that the future will resemble the past. We can’t prove that the laws of nature will continue to operate tomorrow the way they operated yesterday.
We just… assume it. Because what else can we do?
And Sextus saw this. 1,500 years before Hume.
“The foundations of knowledge are far more uncertain than dogmatists admit.”
So let’s take stock of where we are.
We can’t escape infinite regress without arbitrary assumptions. We can’t use circular reasoning without begging the question. We can’t justify induction without using induction.
Every attempt to establish certain knowledge runs into one of these problems.
And this is why Sextus says: Stop trying. Stop clinging to the illusion that you can achieve absolute certainty. Recognize the limits of human knowledge and suspend judgement on claims that go beyond what you can actually justify.
But now—and this is crucial—we have to address the obvious objection.
Slide 8
Because I know what you’re thinking. I know what the objection is.
“Okay, Professor Leshley, this is all very clever. But if I suspend judgement on everything, if I stop believing things with certainty… how do I live? How do I make decisions? How do I get out of bed in the morning?”
“Doesn’t this lead to paralysis? To nihilism? To just sitting in a corner, unable to act because you can’t be certain about anything?”
And this is where we need to understand something absolutely fundamental about Sextus’ philosophy.
“Not Nihilism—A Therapeutic Practice.”
Sextus is not saying you can’t live a normal life. He’s not saying you can’t make decisions or have preferences or act in the world.
He’s saying you can do all of that without dogmatic certainty.
Remember, Sextus was a physician. And he uses medical practice as a model for how the sceptic lives.
A good doctor doesn’t have a rigid theory about how the body works and then force every patient to fit that theory. A good doctor observes. Sees what works. Adjusts treatment based on experience.
If this remedy helps this patient, use it. If it doesn’t, try something else. You don’t need to know why it works. You don’t need a grand theoretical explanation. You just need to pay attention to what actually happens.
Same with the Pyrrhonian sceptic. You don’t need to know the ultimate truth about reality to navigate life successfully. You just need to respond intelligently to appearances, to experience, to what works.
So what does this actually look like in practice?
First: You follow appearances without asserting they’re “true.”
Honey appears sweet to you. Fine. Eat the honey. Enjoy it. You don’t need to make a metaphysical claim about the objective, mind-independent sweetness of honey. You just need to respond to how it appears.
Fire appears hot. Don’t stick your hand in it. You don’t need certain knowledge about the ultimate nature of heat. You just need to respond to the appearance.
Second: You accept customs and conventions pragmatically.
You live in a society with laws, with social norms, with expectations. The Pyrrhonian doesn’t need to believe these are objectively true or absolutely right. You just follow them because… well, because that’s how you function in society.
You stop at red lights not because you have certain knowledge that the traffic laws are metaphysically justified, but because stopping at red lights prevents accidents and that seems like a good idea.
Third: You act on probabilities without claiming absolute knowledge.
This is huge. Sextus isn’t saying you can’t make judgements about what’s likely or unlikely. He’s saying you can’t claim certainty.
Is it going to rain tomorrow? I don’t know with certainty. But the sky is dark, the air feels humid, the weather forecast says 90% chance of rain… so I’ll bring an umbrella.
That’s not dogmatism. That’s just reasonable response to available evidence.
Fourth: You respond to natural inclinations—hunger, thirst, pain, pleasure.
You’re hungry? Eat. You’re tired? Sleep. You’re in pain? Seek relief.
You don’t need a philosophical theory about the nature of hunger to respond to it. You don’t need certain knowledge about the metaphysics of pain to want it to stop.
And here’s what Sextus discovered—and this is the beautiful, counterintuitive heart of Pyrrhonian scepticism:
When you live this way—when you respond to appearances without clinging to dogmatic beliefs about ultimate reality—you experience freedom.
“Freedom from mental conflict and anxiety. Peace that comes from non-attachment to beliefs. Tranquility through suspension of judgement.”
Think about the mental suffering that comes from dogmatic certainty.
You’re absolutely convinced your political ideology is right and everyone else is wrong—so you’re constantly angry at the other side, constantly anxious about them gaining power, constantly in conflict.
You’re absolutely certain about the afterlife—so you’re terrified of death, or you’re judging others for not believing what you believe, or you’re sacrificing present happiness for a future you can’t actually verify.
You’re dogmatically committed to a particular view of how your life should go—so when reality doesn’t match your expectations, you suffer.
All of that suffering comes from attachment. From clinging to beliefs you can’t actually justify with certainty.
And Sextus says: Let go. Not of life, not of action, not of preferences or values or meaning. Just let go of the certainty. Let go of the need to be absolutely right.
And when you do… peace.
Now, this is crucial, and I want to make sure you understand it:
“Sextus doesn’t deny everyday reality—he denies our ability to know the ultimate truth behind appearances.”
He’s not saying tables and chairs don’t exist. He’s not saying your experiences aren’t real. He’s not saying nothing matters.
He’s saying: You experience a table. Fine. Call it a table. Use it as a table. Just don’t make dogmatic claims about its ultimate metaphysical nature—about what it really is, independent of all perception and context.
You experience moral intuitions. You feel that kindness is good, that cruelty is bad. Fine. Act on those intuitions. Just don’t claim you have certain knowledge that these are objective features of reality that everyone must acknowledge.
Live in the world of appearances. Respond intelligently to experience. Just don’t pretend you’ve grasped the ultimate truth behind it all.
Because you haven’t. None of us have.
And admitting that—really admitting it—is the beginning of wisdom.
So that’s Sextus’ vision: A way of life that’s fully engaged with the world, that makes decisions and takes action and has preferences… but that’s free from the anxiety and conflict that comes from dogmatic attachment to unverifiable beliefs.
Now, the question is: Did it work? Did this philosophy actually influence anyone? Did it matter?
Oh, did it ever.
The story of Sextus’ influence is one of the most fascinating in the history of philosophy. And it starts with his books being completely forgotten for over a thousand years…
SLIDE 9: Legacy and Influence
Alright, so we’ve explored Sextus’ philosophy—the methods, the arguments, the way of life. But now I want to tell you a story. Because what happened to Sextus’ ideas after he died is absolutely fascinating.
And it starts with those ideas disappearing completely for over a thousand years.
Picture this: It’s around 200 CE. Sextus Empiricus has just finished writing his major works—the Outlines of Pyrrhonism, Against the Professors—these comprehensive accounts of Pyrrhonian scepticism.
And then… nothing.
The Roman Empire is in decline. Christianity is rising. The intellectual climate is shifting toward religious certainty, toward revealed truth, toward dogmatic theology.
Not exactly the ideal environment for a philosophy that says, “Maybe we should suspend judgement on all dogmatic claims.”
So Sextus’ works get copied a few times, preserved in a few libraries, but they’re not widely read. They’re not influential. For over 1,200 years, Pyrrhonian scepticism is basically a footnote in the history of philosophy.
Until the Renaissance.
1562. A Latin translation of Sextus’ Outlines of Pyrrhonism is published and starts circulating among European intellectuals.
And it explodes.
Because here’s what you have to understand about the intellectual climate of 16th-century Europe: This is the age of religious warfare. Catholics versus Protestants. Each side absolutely certain they have the truth. Each side willing to kill and die for their certainty.
And into this environment comes Sextus Empiricus saying: “How do you know you’re right? What’s your criterion? Can you prove it without circular reasoning or infinite regress?”
It’s like throwing a philosophical grenade into the middle of a theological war.
Suddenly, intellectuals across Europe are reading Sextus and thinking: “Wait. The ancient Greeks—these brilliant philosophers we’ve been revering—they couldn’t achieve certainty about fundamental questions. They had all these arguments showing that knowledge is impossible or at least deeply problematic.”
“So what makes us think we can do better?”
The most famous example is Michel de Montaigne—French nobleman, essayist, one of the most influential thinkers of the Renaissance.
Montaigne reads Sextus and has this profound intellectual conversion. He adopts as his personal motto: “Que sais-je?”—”What do I know?”
And he writes these brilliant essays that are basically Pyrrhonian scepticism applied to everything: morality, religion, politics, human nature, cultural practices.
He asks: How do we know our customs are better than those of the indigenous peoples being discovered in the New World? How do we know our religion is the true one when people in other cultures believe just as fervently in theirs? How do we know animals don’t have rational souls when we can’t even define what a rational soul is?
And what’s radical about Montaigne is that he’s not using scepticism to tear everything down. He’s using it to cultivate tolerance, humility, openness.
He’s saying: If we admitted how little we actually know with certainty, maybe we’d stop killing each other over theological disagreements.
Scepticism as a path to peace. Just like Sextus promised.
But Sextus’ influence doesn’t stop with Montaigne. In fact, you could argue that the entire project of modern philosophy—from Descartes onward—is a response to the sceptical crisis that Sextus helped create.
Descartes reads the sceptics and freaks out. He realizes that all his beliefs could be wrong. So he develops his method of radical doubt—doubt everything until you find something absolutely certain.
And what does he find? “Cogito ergo sum”—”I think, therefore I am.”
The one thing he can’t doubt is that he’s doubting. The one certainty is the existence of the thinking self.
Now, Sextus would have problems with this—he’d ask how Descartes knows that thinking requires a thinker, how he knows the “I” persists from one moment to the next—but the point is: Descartes is responding to Sextus. He’s trying to rebuild certainty in the face of sceptical arguments.
Then you get David Hume in the 18th century, and he basically revives Sextus’ problem of induction.
Hume says: We can’t justify our belief that the future will resemble the past. We can’t prove that natural laws will continue to operate. All our scientific knowledge rests on a foundation we can’t rationally justify.
This is pure Sextus. And it creates another crisis in philosophy.
Which leads to Kant, who spends his entire critical philosophy trying to answer Hume—trying to show how we can have genuine knowledge while acknowledging the limits of human reason.
The whole architecture of modern epistemology—the study of knowledge—is built on questions that Sextus raised 1,800 years ago.
But here’s what I want you to understand: This isn’t just history. Sextus is relevant today. Maybe more relevant than ever.
We live in an age of absolute certainty. Everyone has an opinion about everything, and everyone’s sure they’re right.
Political polarization—each side convinced the other is not just wrong but evil. Conspiracy theories—people absolutely certain they’ve seen through the lies. Online arguments where nobody ever changes their mind because everyone’s too invested in being right.
And what does Sextus offer?
“Epistemology, fallibilism, intellectual humility. Critical thinking and scientific method. Cognitive biases and the limits of human reasoning.”
Epistemology—the study of how we know what we know. Sextus forces us to examine our assumptions about knowledge itself.
Fallibilism—the recognition that we could be wrong. That our beliefs are provisional, subject to revision.
Intellectual humility—the willingness to say “I don’t know” or “I’m not sure” instead of pretending to certainty we don’t actually have.
Critical thinking—the ability to examine arguments on both sides, to recognize when evidence is insufficient, to suspend judgement when appropriate.
Scientific method—which is fundamentally sceptical. Science doesn’t prove things true; it provisionally accepts hypotheses that haven’t been falsified yet.
Cognitive biases—modern psychology has shown us all the ways our reasoning goes wrong. Confirmation bias, motivated reasoning, the Dunning-Kruger effect… Sextus would recognize all of this.
We need Sextus today. We need his reminder that certainty is often unjustified. That intellectual humility is a virtue. That you can live a meaningful, engaged life without claiming to have all the answers.
SLIDE 10: The Enduring Wisdom of Sextus Empiricus
So let me bring this home. After everything we’ve explored—the methods, the arguments, the way of life, the historical influence—what’s the enduring wisdom of Sextus Empiricus?
What can we take from this ancient physician-philosopher that actually matters for how we live today?
I think it comes down to three core lessons.
First: Question certainty. Especially your own.
Look, I’m not saying you can’t have beliefs. I’m not saying you can’t have strong convictions. But I am saying: Be honest about the difference between “I believe this” and “I know this with absolute certainty.”
When you find yourself thinking, “I’m obviously right about this”—pause. Ask yourself: What would it take to change my mind? Have I genuinely considered the strongest arguments on the other side? Or am I just surrounding myself with people who already agree with me?
Genuine inquiry—real intellectual honesty—requires openness to being wrong. It requires the willingness to say, “I could be mistaken about this.”
And here’s what Sextus understood: That’s not weakness. That’s wisdom.
“‘I could be mistaken’ is a mark of wisdom, not weakness.”
The people who are most certain are often the most wrong. The people who admit uncertainty are often closer to truth.
Second: Find inner peace through non-attachment to beliefs.
This is the therapeutic heart of Sextus’ philosophy, and it’s profoundly relevant today.
Think about how much mental suffering comes from clinging to beliefs. From needing to be right. From the anxiety of defending positions you’re not actually certain about. From the conflict that arises when your beliefs clash with someone else’s.
What if you could let that go?
Not the beliefs themselves, necessarily. Not your values or your preferences or your sense of meaning. Just the attachment. Just the desperate need for certainty.
“You can act decisively without absolute certainty.”
This is huge. You don’t need to know the ultimate truth about morality to act morally. You don’t need metaphysical certainty about the nature of justice to fight for justice. You don’t need absolute proof that your life has meaning to live meaningfully.
You just need to respond honestly to your experience, to your values, to what appears good and right and true—while remaining open to the possibility that you might be wrong.
And when you do that—when you hold your beliefs lightly instead of clinging to them desperately—you experience what Sextus promised: ataraxia. Peace. Tranquility.
Not because you’ve given up. But because you’ve stopped suffering over things you can’t actually control—like whether your beliefs correspond to ultimate reality.
Third: Embrace intellectual humility.
This is maybe the most important lesson. And it’s the hardest one.
We live in a culture that rewards confidence. That celebrates people who speak with authority, who never admit doubt, who always have an answer.
But Sextus reminds us that true wisdom lies in recognizing the limits of human knowledge.
“True wisdom lies in knowing what you don’t know.”
This goes back to Socrates, right? “I know that I know nothing.” But Sextus takes it further. He gives us a method, a practice, a way of life built on that recognition.
And here’s what I want you to understand: Intellectual humility doesn’t mean you can’t have expertise. It doesn’t mean all opinions are equally valid. It doesn’t mean you can’t make judgements or take stands.
It means you recognize that your knowledge is limited. That your perspective is partial. That you could be wrong. That there might be considerations you haven’t thought of, evidence you haven’t encountered, arguments you haven’t heard.
It means you approach disagreement with curiosity instead of defensiveness. You ask questions instead of just asserting. You listen instead of just waiting for your turn to talk.
And most importantly—most importantly—it means you examine your own certainties.
“The examined life includes examining your own certainties.”
The beliefs you’re most confident about? Those are the ones that most need examination. Because those are the ones you’ve probably stopped questioning.
So let me end with Sextus himself. With his own words about what the sceptical art actually is.
“The sceptic’s art is the ability to oppose phenomena and noumena in any way whatsoever, with the result that, owing to the equal force of the objects and reasons opposed, we are brought to suspend judgement and then to peace of mind.”
Phenomena and noumena—appearances and reality. The world as we experience it and the world as it supposedly is “in itself.”
Sextus is saying: We can always oppose these. We can always show that our claims about ultimate reality are balanced by equally strong counter-claims.
And when we genuinely see that balance—when we really grasp that the arguments on both sides have equal force—we naturally suspend judgement.
Not because we’re forced to. Not because we’re being intellectually dishonest. But because… what else can we do? How can we claim certainty when the evidence doesn’t support it?
And then—then—we experience peace.
Not the peace of having all the answers. Not the peace of being absolutely certain. But the peace of letting go. The peace of non-attachment. The peace of intellectual humility.
The peace of knowing that you don’t have to have everything figured out to live a good life.
Look, I’m not going to stand here and tell you that you should become a full-on Pyrrhonian sceptic. I’m not even sure that’s possible in the modern world—or desirable.
But I am going to tell you this: The next time you find yourself absolutely certain about something—especially something important, something you’re willing to argue about or judge others over or base major life decisions on—ask yourself Sextus’ questions.
What’s my evidence? What are the counter-arguments? Could I be wrong? Am I clinging to this belief because it’s true, or because it’s comfortable? Because it’s well-supported, or because it’s part of my identity?
And if you find that you can’t justify your certainty—if the arguments really do balance out—try suspending judgement. Just for a moment.
See what it feels like. See if Sextus was right about the peace that comes from letting go.
You might be surprised.
Or you might not. And that’s okay too.
Because the point isn’t to achieve some perfect state of sceptical enlightenment. The point is to cultivate intellectual honesty. To recognize our limits. To hold our beliefs with humility instead of arrogance.
And if a 2nd-century Roman physician could figure that out—if he could develop a philosophy that’s still relevant 1,800 years later—maybe, just maybe, there’s something to this ancient art of doubt after all.
Thanks for thinking with me today. Stay curious. Stay humble. And remember: It’s okay not to know.
In fact, it might be the wisest thing you can admit.
Thank you