When Saying "I Know" Actually Means Something

Imagine you’re sitting in class and your friend whispers, “Do you know the answer to number five?” You say yes, and then you realize you’re not totally sure. You think it’s B, but maybe it’s C. Did you really know? Or were you just pretty confident?

This might seem like a small thing, but it turns into a surprisingly deep question: What does it actually mean to know something? And when can you be sure you know it?

About 2,100 years ago, a group of philosophers in Athens got into a fight about this that went on for decades. The fight is still happening today. And one of the key figures in the middle of it was a man named Antiochus of Ascalon—a guy who changed his mind completely about knowledge, fell out with his teacher, and started his own school. Here’s what happened.

The School That Said “We’re Not Sure”

To understand Antiochus, you first need to understand the weird situation he grew up in. He was a member of something called the Academy, which was a school founded by Plato (yes, that Plato) back in the 300s BCE. By Antiochus’s time, around 100 BCE, the Academy had become skeptical. That means the philosophers there spent a lot of time arguing that humans can’t really know anything for sure.

This wasn’t just being grumpy. They had good reasons. Think about how often you’ve been absolutely certain about something and turned out to be wrong. That thing you saw out of the corner of your eye that turned out to be a coat on a hook. That fact you’d have bet money on that your friend later proved was false. The Academic skeptics said: if we’ve been wrong so many times before, how can we ever be sure we’re not wrong right now? Maybe the best we can do is say “this seems true” without claiming to know it.

For a long time, Antiochus agreed with this. He was a loyal student of Philo of Larissa, the head of the Academy, and he defended the skeptical position in his own writings.

Then something changed.

The Break

We don’t know exactly when or why, but at some point Antiochus decided the skeptics were wrong. He came to believe that knowledge is possible—that humans really can be certain about some things.

This was a big deal. Imagine if your best friend, who has always agreed with you about everything, suddenly announced you were wrong about something you both deeply believed. That’s what happened, but with higher stakes. Antiochus didn’t just change his own mind. He started arguing that the entire Academy had gone off track. The real Academy, he said, was the “Old Academy” of Plato and his first followers, who had believed knowledge was possible. The skeptics who came later—including his own teacher—had betrayed the school’s true tradition.

This made a lot of people angry. Some of his former friends accused him of not really being an Academic at all. They said he was actually a Stoic—a member of a rival school of philosophy—which was basically an insult.

That accusation makes more sense when you look at what Antiochus actually believed.

The Stoic Idea of Knowledge

The Stoics had a very specific theory about what knowledge is and how you get it. Antiochus basically took their theory and claimed it was actually what the Old Academy had believed all along. (Historians still argue about whether he was right about this.)

Here’s the Stoic theory in simple terms.

Imagine you’re looking at a red apple on a table in good light. The impression you get—“that’s a red apple”—is what the Stoics called a cognitive impression. That’s just a fancy way of saying it’s an impression that (1) comes from something real, (2) exactly matches what it came from, and (3) is so clear and distinct that it couldn’t possibly come from anything else.

The Stoics believed that if you only ever give your mental “yes” to impressions like this—and withhold judgment when your impressions are fuzzy or could be wrong—you can never make a mistake. You can build a life entirely free of false beliefs. That was their definition of wisdom.

Now, the Academic skeptics had spent generations arguing that no such impressions exist. They said you could never be sure an impression really met all those conditions. Maybe it looks like a real apple, but how do you know it’s not a perfect wax apple? How do you know you’re not dreaming? The skeptics had arguments for this that were very hard to answer.

Antiochus thought the skeptics were wrong. He defended the Stoic idea that cognitive impressions are real and that we genuinely have them. But here’s the strange part: he did this while still claiming to be an Academic, the very school that had spent two centuries arguing against exactly this.

Why This Matters for Real Life

This might sound like a very old, very dead argument between people in togas. But the question at its heart is still alive: Can you ever be completely sure about something?

Think about how you decide what’s true. When you’re online, how do you know a piece of information is reliable? When a friend tells you something, when do you accept it and when do you doubt it? When you memorize something for a test, do you know it, or do you just have a strong feeling that you’re right?

Here’s a specific example. Imagine you’re playing a video game where you have to jump across a gap. You’ve done it a hundred times. You know you can make it. But then one time, you don’t. Does that mean you never really knew? Or does it mean you knew, but something unexpected happened?

The skeptics would say: you never really knew—you just felt confident based on past experience, and confidence isn’t the same as knowledge. Antiochus would say: you knew, because your past experience gave you a genuine cognitive impression of the gap that let you judge correctly. (The one time you failed doesn’t erase the hundred times you succeeded.)

The Cradle Argument

Antiochus also had things to say about ethics—about how we should live. And here, too, he took ideas from the Stoics and twisted them to fit his own view.

The Stoics and their rivals used something called the “cradle argument” to figure out what’s good for humans. The idea was: watch a baby. A baby hasn’t been corrupted by society yet. What does a baby naturally go for? Whatever that is, it’s probably what’s genuinely good for humans.

The Epicureans said babies go for pleasure, so pleasure is the goal of life. The Stoics said babies go for “natural advantages”—things like health, being warm, having enough to eat, not being in pain. But the Stoics drew a surprising conclusion. They said that while babies naturally want these things, they’re not actually good in the ultimate sense. They’re just preferred. The only real good, according to the Stoics, is virtue—being a wise and good person.

Antiochus disagreed with this. He thought the Stoics were being weirdly extreme. If health makes life better, and sickness makes it worse, then health is a good thing. Period. Virtue is the most important good, but it’s not the only good. A life with virtue and health is better than a life with virtue but no health.

This might not sound radical, but it was a real fight. The Stoics thought Antiochus was caving in to common sense instead of following logic wherever it led. Antiochus thought the Stoics were ignoring obvious facts about human life.

The Weirdest Twist: Virtue Is Enough, But Also Not Enough

Here’s where Antiochus’s position gets genuinely strange and interesting. He wanted to have it both ways.

On one hand, he said that virtue—being a good person—is sufficient for happiness. If you’re virtuous, you’re happy, period. Full stop. Your life counts as a good life no matter what happens to your body or your circumstances.

On the other hand, he also said that there are other goods besides virtue—health, friends, enough money to live on—and having these things makes your life more happy. More completely happy. The happiest possible life requires both virtue and these other goods.

So is virtue enough or isn’t it? Antiochus said yes to both. He distinguished between the “happy life” (which virtue alone gives you) and the “completely happy life” (which requires other goods too). You can be happy without being maximally happy.

Philosophers argued about whether this made any sense. Some said it was a cheat—that you can’t have it both ways. Others said it was a realistic picture of human life, where we can be genuinely happy while also recognizing that things could be better.

The Impossibility of Arguing Without Believing

There’s one more piece of this story that’s worth thinking about.

Antiochus argued that the skeptics’ position was self-refuting. If you say “nothing can be known,” you have to be claiming to know that in order to say it. But if you’re claiming to know that nothing can be known, you’re contradicting yourself—you’re claiming to know something while saying nothing can be known.

The skeptics had responses to this. Some said they didn’t claim to know it—they just found it highly probable. Others said they didn’t even claim that—they just kept asking questions without committing to any answers at all.

But Antiochus’s basic challenge is still interesting: Can you argue that nobody should be certain about anything, without being certain that you’re right?

Think about this in everyday life. When someone says “you can’t be sure of anything,” what should you make of their claim? Should you be sure they’re right? If you’re not sure they’re right, then maybe some things can be known. If you are sure they’re right, well, then you just contradicted yourself.

Philosophers still argue about this. There’s no obvious way out.

Why Bother?

Here’s the thing about Antiochus and his fights with the skeptics. The real issue wasn’t technical details about impressions or definitions of knowledge. The real issue was: how should you live, given that you could be wrong about almost anything?

If the skeptics are right and you can’t really know anything, then maybe you should always hold back, always doubt, never commit fully to any belief. That’s one way to live.

If Antiochus is right and knowledge is possible, then you can commit to what you know, build on it, and act with confidence. That’s another way to live.

Neither position is obviously correct. Most people today live somewhere in between—they’re sure about some things and doubtful about others. But where you draw that line, and how you decide, is a question that never goes away.

Antiochus, for what it’s worth, died in 68 BCE, still arguing that he was the true heir of Plato, still insisting that knowledge was real, still claiming that the skeptics had it all wrong. Whether he was right or wrong depends on what you think about knowledge—which means it depends on how you answer the very question he spent his life fighting about.

Key Terms

Term	What it does in this debate
Academy	The school Plato founded; by Antiochus’s time, most members were skeptics
Skepticism	The view that humans can’t really know things for certain
Cognitive impression	A mental experience that is so clear and accurate it can’t be from anything false; the Stoics thought these exist, the skeptics didn’t
Cradle argument	The idea that you can figure out what’s good for humans by watching what babies naturally want
Virtue	Being a wise and good person; for the Stoics, the only real good; for Antiochus, the most important good

Key People

Plato (c. 428–348 BCE): Founded the Academy and wrote dialogues about knowledge, justice, and reality. His views became the battleground everyone later fought over.
Antiochus of Ascalon (c. 130–68 BCE): Started as a skeptic, then switched to believing knowledge is possible, and claimed he was the true heir of Plato—not the skeptics.
Philo of Larissa: Antiochus’s teacher and the head of the Academy before Antiochus broke with him; defended a moderate form of skepticism.
Zeno of Citium (c. 334–262 BCE): Founded Stoicism; argued that cognitive impressions exist and that knowledge is possible.

Things to Think About

Does saying “I’m sure” actually make you sure? Or is there a difference between feeling certain and really knowing?
If you had to choose between living as a skeptic (always doubting, never committing) or a dogmatist (being confident about many things, but sometimes wrong), which would you pick? Why?
Antiochus said virtue alone makes you happy, but other goods make you more happy. Does that seem right to you, or does it feel like cheating? Can you be happy without being completely happy?
Can you think of a time when you were absolutely certain about something and turned out to be wrong? Did that change how you think about whether you really know things now?

Where This Shows Up

In school debates about evidence: When you’re writing an essay or analyzing a source, you’re basically asking: “How sure can I be about this? What counts as good evidence for what I claim to know?”
In arguments with friends: Next time someone says “I know I’m right,” notice whether they’re really claiming knowledge or just strong opinion. Notice whether you can tell the difference.
In science: Scientists don’t claim to know things with absolute certainty; they talk about confidence, probability, and evidence. This is basically living in the space between Antiochus and the skeptics.
In everyday decisions: When you decide whether to trust someone, or whether to believe a rumor, or whether to act on something you think you know, you’re making a practical decision about knowledge—whether you realize it or not.