Could You Be Certain of Anything?

Imagine you’re sitting in your room right now. You can see a window, a chair, maybe a book. You can feel the floor under your feet. You probably think you know that these things are real, that you’re actually there, that you’re not dreaming.

But how certain are you, really?

Could you prove it? Not just “I’m pretty sure,” but prove it — the way you can prove that 2 + 2 = 4? If someone demanded absolute certainty, no doubt allowed, could you give it to them?

Nearly seven hundred years ago, a philosopher in Paris named Nicholas of Autrecourt (roughly 1295–1369) asked this question seriously. And his answer shook up his whole world so much that the Church forced him to burn his own writings and publicly take back what he’d said.

Here’s what got him into trouble.

The Problem: What Can You Really Prove?

Autrecourt started with a simple idea that sounds reasonable: You should only claim to know something for certain if you can prove it beyond all doubt. And the strongest proof there is, he thought, is a contradiction. You know that a statement can’t be both true and false at the same time. That’s the rock-bottom foundation of logic. So if denying something would force you into a contradiction, then you can be certain of it.

That seems fine. But then Autrecourt looked at what we normally think we know — and found almost nothing that passes this test.

Take cause and effect. You see a fire and you feel heat. You probably think the fire causes the heat. But is it contradictory to say “the fire is there but there is no heat”? No. It’s not a contradiction. It might not be how the world actually works, but it’s not impossible to imagine. So you can’t prove the connection with absolute certainty.

Take substances. You see a white, round, sweet thing. You think “that’s a sugar cube” — a substance that has those properties. But can you prove the substance exists just from the properties you experience? Again, no. It’s not contradictory to say “I see something white, round, and sweet, but there’s no substance underneath it.” You can’t be certain.

Take other people’s minds, or even whether your own body exists. Autrecourt pointed out to his fellow philosopher Bernard of Arezzo (who had even more radical doubts) that if you follow certain kinds of skepticism to their logical end, “you do not know if you are in the sky or on earth, in fire or in water… you do not know what things exist in your immediate surroundings, such as whether you have a head, a beard, hair, and the like.”

This is unsettling. If the only things you can be certain of are things whose denial would be a contradiction, then you can’t be certain of almost anything about the physical world. You can’t be certain that causes produce effects. You can’t be certain that objects have hidden “substances” underneath their appearances. You might not even be certain that your own body exists.

That’s the problem Autrecourt identified. And it bothered a lot of people.

But Wait: Autrecourt Wasn’t a Skeptic

Here’s where it gets interesting. Autrecourt is famous for raising these doubts, but he didn’t actually accept them. He didn’t think we should all walk around questioning whether our heads exist. He just thought that we can’t prove these things with absolute, contradiction-based certainty.

In fact, Autrecourt argued quite strongly that our senses are reliable. He thought that when you see something clearly — in what he called “the full light” — you can trust what you see. If something appears red to you, it is red in that moment. The problem of illusions and dreams? He had an answer for that.

Here’s his move: He said we need to separate the appearance itself from the judgment we make about it. If something looks bitter to you, the appearance itself is real — you really are having that experience. The mistake comes when you judge “this object is bitter” without realizing the conditions might be off. (Maybe you’re sick, or the lighting is weird, or you’re looking at it through a dirty glass.)

So appearances themselves are always true. You can be certain that things appear to you the way they do. The only room for error is in what you conclude from those appearances.

But then a new problem arises: How do you tell the difference between a clear appearance (when conditions are normal) and a distorted one? How do you know when to trust your judgment?

Autrecourt’s answer here is honest but unsatisfying: You just can tell. It’s built into how your mind works. The same way you just know that white and black are different without proving it, you just know when you’re seeing something clearly. There’s no further proof you could give. At some point, you have to trust that your basic cognitive equipment works.

This is what philosophers call the “problem of the criterion” — you need a way to judge whether your judgments are correct, but you’d need a judgment to evaluate that, which creates an infinite loop. Autrecourt just said: at some point you stop. You accept that some things are just evident to you.

Why This Mattered (and Still Matters)

Autrecourt’s ideas got him into deep trouble. In 1340, the Pope summoned him to defend himself against accusations of false teaching. By 1346, a commission had found 66 of his claims to be “false, dangerous, presumptuous, suspect, erroneous, and heretical.” He was forced to publicly recant — to stand up and say he was wrong. His writings were burned. He was banned from ever becoming a master of theology.

What made his views so threatening? Partly it was the challenge to Aristotle, whose philosophy was the backbone of university teaching. Aristotle thought we could discover causal relationships through observation and induction. Autrecourt said no — logic doesn’t give us that certainty.

But the deeper threat might have been about faith. If you can’t be certain about ordinary cause and effect, what about claims about God, miracles, or the soul? Autrecourt carefully said he was only talking about what reason alone could prove — faith was different. But the Church wasn’t convinced that his ideas could be kept in a neat box.

What’s Still Unsettled

Even today, philosophers still argue about these questions. David Hume, an 18th-century Scottish philosopher, made similar points about causality: we never actually see a cause, we just see one thing following another and get used to the pattern.

Some philosophers today, called “skeptics” (from the Greek word for “looking”), think Autrecourt was right that we can’t prove much with absolute certainty. Others think he set the bar too high — that we can have good enough reasons for knowledge without needing contradiction-proof certainty.

Still others argue that we can prove causality or substance, using more sophisticated logic than Autrecourt considered. The debate continues.

So What Should You Think?

Autrecourt didn’t want you to stop trusting your senses. He wanted you to be honest about what you can and can’t prove. There’s a difference between “I know this for certain” and “I’m extremely confident about this based on experience.”

The next time you’re absolutely sure about something — that your friend is angry, that the ice will melt, that the sun will rise — ask yourself: could I prove this beyond all contradiction? If not, does that mean I shouldn’t be confident? Or does it mean “certainty” comes in different strengths?

Autrecourt’s fundamental lesson might be this: It’s okay to be less certain than you thought you were. You don’t need absolute proof to live your life. Just don’t pretend you have it when you don’t.

Appendix: Key Terms

Term	What it does in this debate
Contradiction	The gold standard of proof for Autrecourt — if denying something creates a contradiction, you can be certain of it
Cause and effect	The relationship between one event and another that seems to produce it — Autrecourt argued we can’t prove this with certainty
Appearance	What you directly experience through your senses — Autrecourt thought appearances themselves are always true
Judgment	The conclusion you draw from an appearance — this is where errors happen, according to Autrecourt
Substance	The hidden “something” that supposedly underlies all the properties you can perceive — Autrecourt doubted we could prove it exists
Problem of the criterion	The tricky question of how you know whether your method for judging is correct, without already needing a correct method to evaluate it

Appendix: Key People

Nicholas of Autrecourt (c. 1295–1369) — A French philosopher and theologian who argued that only contradictions can give us absolute certainty, and was condemned for his views.
Bernard of Arezzo — A Franciscan theologian who debated with Autrecourt and took an even more extreme skeptical position, doubting even the reliability of sense experience.
David Hume (1711–1776) — A Scottish philosopher who later made many of the same points about causality and skepticism, earning Autrecourt the nickname “the medieval Hume.”

Appendix: Things to Think About

Autrecourt said you can be certain of your own sensory experiences but not of what causes them. Is there a real difference between “the soup tastes salty” and “the soup is salty”? Or are those the same thing dressed up differently?
If you can’t prove that causes produce effects with absolute certainty, how should that affect how you live? Should you stop trusting that flipping a light switch will turn on the light? Or is that kind of confidence still rational even if it’s not “proven”?
Autrecourt thought we just know when we’re seeing clearly — there’s no proof we can give for why clear appearances are trustworthy. Does that bother you? Or is it okay for some things to be just fundamentally built into how we think?
The Church forced Autrecourt to publicly take back his ideas. Should ideas be suppressed because they’re dangerous or unsettling? Or should only false ideas be suppressed — and who gets to decide which are false?

Appendix: Where This Shows Up

In science: Scientists talk about “correlation” (two things happen together) versus “causation” (one thing makes the other happen). Autrecourt’s point — that you can’t directly observe causation — is still a basic problem in how science works.
In court: Legal proofs like “beyond a reasonable doubt” are weaker than the “contradiction-proof” certainty Autrecourt demanded. What counts as enough proof changes depending on the situation.
In arguments with friends: If someone says “prove it,” they might be demanding a kind of certainty that nobody can actually give. Figuring out what kind of proof is reasonable in a given situation is a skill Autrecourt’s ideas can help you think about.
In conspiracy theories: People sometimes say “you can’t prove that’s not true.” Autrecourt would say that’s a bad standard — you can’t prove most negatives with absolute certainty either.