Buridan and the Ass That Couldn't Decide

Here’s a strange thing about medieval universities: students as young as 14 or 15 would show up, often barely speaking Latin, and within a few years they were supposed to be arguing about the deepest questions in philosophy. They didn’t have textbooks the way we do. Instead, a master would read aloud from Aristotle’s works and explain them line by line. The students would argue back. Their arguments got written down. And sometimes, out of those arguments, new ideas were born.

John Buridan was one of those masters. He taught at the University of Paris in the 1300s, and his students carried his ideas across Europe. Today, most people who have heard of him know only one thing: “Buridan’s Ass” — a donkey that starves to death because it can’t choose between two equally good piles of hay. But Buridan never actually wrote about any donkeys starving. The story was made up later, probably as a joke at his expense. What Buridan actually thought about choice, logic, and why we make decisions turns out to be far more interesting than the cartoon version.

What Do Words Really Mean?

Imagine you say, “Man is a species.” That sounds straightforward enough. But think about it: no individual man is a species. Socrates is a man, not a species. Your friend Ahmed is a man, not a species. So if “man” normally refers to individual human beings, how can the word “man” in that sentence be talking about something that isn’t any individual person?

Medieval philosophers spent a lot of time on puzzles like this. They noticed that words can do different things in different sentences. When you say “Man has three letters,” you’re not talking about a person at all — you’re talking about the word itself. When you say “Man is an animal,” you’re talking about actual people. But when you say “Man is a species,” what are you doing?

Before Buridan, many philosophers thought that sentences like “Man is a species” proved that there must be something called “humanity” that exists separately from individual humans — a universal thing that all humans share. They called this “simple supposition” (supposition was their word for what a term stands for in a proposition).

Buridan thought this was a mistake. He argued that there are only two ways a term can function in a sentence. Either it stands for the actual things it normally signifies (like “man” standing for actual people), or it’s being used in some special way — to refer to itself, to a concept, or figuratively. He called both of these “material supposition.” There’s no need to invent spooky universal entities just because of how we talk.

“An utterance does not have any proper power of signifying except from us,” Buridan wrote. Words mean what we agree they mean. When you say “Man is a species” while studying Aristotle’s Categories, you’re following the author’s lead and using “man” in a special way. That’s fine — it’s true in that context. But you haven’t discovered a thing called “humanity” floating around somewhere. You’ve just described how we organize our concepts.

This might seem like a small point, but it’s part of a bigger move Buridan made. He thought that many philosophical problems come from taking language too literally. People hear a sentence like “God is the cause of Socrates” and think there must be something — a thing called “God’s-being-the-cause-of-Socrates” — that exists alongside God and Socrates. Buridan said: no. You’re just confused by your own words. The proposition means what it means; you don’t need to invent new entities to match every phrase.

The Donkey That Never Was

So where does the starving donkey come in?

The story, which someone made up after Buridan’s death, goes like this: A donkey stands exactly halfway between two identical piles of hay. Both piles look and smell exactly the same, and are the same distance away. The donkey has no reason to choose one over the other. So it just stands there, unable to decide, and starves to death.

The joke was probably aimed at Buridan’s views about free choice. Buridan argued that when you’re faced with two equally good options, you can simply defer — decide not to decide yet, and think it over further. The will can say to the intellect: “I’m not sure which is better; let me keep thinking.” This sounds reasonable enough for humans. But for a donkey? A donkey would starve.

The joke stuck, even though Buridan never said anything about donkeys. Versions of the puzzle actually go back to Aristotle, who talked about a man who was equally hungry and thirsty but couldn’t choose between food and water. But the name stuck to Buridan because of his particular view about how choice works.

How Does Choice Actually Work?

Here’s where Buridan’s real view gets interesting. There was a big argument in medieval philosophy about whether the will can ever act independently of the intellect. The intellectualists (like Thomas Aquinas) thought the will always follows what the intellect judges to be good. The voluntarists (like Duns Scotus and William of Ockham) thought the will could sometimes choose differently from what the intellect recommends — even choosing something it knows is worse.

Buridan tried to split the difference. He said that human happiness ultimately consists in thinking, not in willing. The best thing we can do is understand God, not just love him. That sounds intellectualist. But he also said the will has a special power: it can say “hold on, let me think about this more” and refuse to act until the intellect is certain.

This seems like real freedom. But Buridan added a crucial detail: the will can only defer if the intellect judges that deferring is good. So even the act of “not deciding” is guided by the intellect. If the intellect says “hey, it would be good to think about this more,” then the will can postpone. But if the intellect says “nope, going right is clearly better,” the will has to go right.

So Buridan’s compromise is really intellectualism in disguise. The will never overrules the intellect. It just sometimes follows a particular judgment — “it’s worth thinking more” — instead of a judgment about which hay pile is better. But that’s still the intellect making the call.

Why would Buridan pretend otherwise? Probably because in 1277, just a few decades before Buridan was born, the Bishop of Paris had condemned a bunch of philosophical ideas — including some versions of intellectualism that seemed to leave no room for free will. Philosophers who seemed to say “the intellect determines everything” risked being accused of denying human freedom and moral responsibility. So Buridan may have used voluntarist language (“the will can defer!”) to keep himself safe, while actually maintaining an intellectualist position (“but only when the intellect tells it to”).

How to Tell If You’re Lying to Yourself

One of the most interesting things Buridan studied was self-reference — sentences that refer to themselves. This gets weird fast.

Consider this: Someone says “Every proposition is false.” But that proposition itself is a proposition. So if it’s true, then it must be false (because it says all propositions are false, including itself). And if it’s false, well, maybe that’s fine? But then does that mean some other proposition is true? How would we know?

This is an ancient puzzle called the Liar Paradox. Medieval philosophers called it an insolubile — an unsolvable puzzle. Buridan taught his students how to handle these.

His first idea was that every proposition, by its very nature, asserts that it is true. So “Every proposition is false” is false because it asserts both “I am true” (implicitly) and “I am false” (explicitly), and those can’t both be right.

But Buridan later changed his mind. He realized that not every proposition asserts its own truth. “A man is an animal” doesn’t say anything about itself — it’s about men and animals. So his earlier solution relied on a false claim about all propositions.

His final solution was more elegant. A proposition is true if two conditions are met: (1) its subject and predicate terms stand for the same things, and (2) the proposition logically implies that it is true, and that implied proposition is also true. For the liar sentence “Every proposition is false,” the first condition might be met (in the imagined scenario, all propositions are false, so “every proposition” and “false” do stand for the same things). But the second condition fails: the sentence cannot imply its own truth without contradiction.

This might sound technical, but the upshot is important. Buridan took self-reference seriously. He didn’t just ban it or say “you’re not allowed to talk about your own sentences.” He recognized that people actually do make self-referential statements, and a good logic should be able to handle them. This is very different from other logicians of his time, who tried to restrict what terms could refer to to avoid the problem. Buridan thought: if someone says something, we should try to understand what they mean, not tell them they’re not allowed to say it.

How Do You Know Anything at All?

Buridan lived at a time when some philosophers were becoming skeptical about whether we can really know anything. One of his contemporaries, Nicholas of Autrecourt, argued that the only things we can be certain of are whatever follows from the principle of non-contradiction (you can’t say the same thing is both true and false at the same time in the same way). According to Nicholas, we can’t even be sure that one thing causes another — we just see one thing happening after another and assume a connection.

Buridan thought this was ridiculous. He was an empiricist: he trusted what our senses tell us, most of the time. He admitted that God could, in theory, deceive us in ways we could never detect. But he pointed out that our ordinary powers of perception and reasoning are actually pretty reliable. We can know things about the world, even if we can’t prove them with absolute certainty by starting from the principle of non-contradiction.

“Natural science is about what happens for the most part,” Buridan said. We don’t need absolute certainty to have knowledge. We need good evidence, careful reasoning, and an understanding that our conclusions might need to be revised. This sounds a lot like how modern science actually works.

What Happened to Buridan’s Ideas?

Buridan never studied theology or became a doctor of the church. He spent his whole career in the faculty of arts, teaching logic and philosophy to teenagers. This was unusual — most smart medieval philosophers moved on to theology, which was considered the highest discipline. Buridan seems to have chosen to stay in arts, perhaps because he thought philosophy should be a secular enterprise based on evidence and reason, not on faith.

His logic textbook, the Summulae de Dialectica, became incredibly popular. It was used at universities across Europe for centuries. His students carried his ideas to new universities in Heidelberg, Prague, and Vienna. His approach to logic — always attentive to how real people actually speak and argue, rather than trying to force language into an ideal form — influenced philosophy well into the Renaissance.

Buridan died sometime after 1358, probably in his late fifties or early sixties. We don’t know exactly when or how. The legends say he was thrown in the Seine in a sack by the King of France (for having an affair with the queen), or that he founded the University of Vienna, or that he once hit the future Pope Clement VI over the head with a shoe. None of these stories can be confirmed. But they show that even after his death, Buridan remained someone people wanted to talk about.

The donkey legend persists too. It’s a useful thought experiment, even if Buridan never used it. It raises real questions: What does it mean to make a choice? Can reason always guide us? What happens when reasons run out?

Buridan’s own answer — that we can always defer and think more — might seem unsatisfying. After all, sometimes you have to choose. The donkey, if it existed, would starve. But Buridan wasn’t talking about donkeys. He was talking about human beings, who can always ask another question, consider another angle, and decide that, actually, it’s worth trying to figure out which hay pile is better before eating. His point was that freedom isn’t about choosing arbitrarily. It’s about being able to stop and think before acting.

That might not be the most dramatic version of free will. But it might be the one that actually describes how we live.

Key Terms

Term	What it does in this debate
Supposition	The way a term “stands for” something in a proposition — its reference in context
Personal supposition	When a term stands for the actual things it normally signifies (e.g., “man” in “Socrates is a man”)
Material supposition	When a term stands for itself, a concept, or is used in some special sense (e.g., “man” in “Man has three letters”)
Ampliation	When a term’s reference is extended to include past, future, or possible things (e.g., “man” in “Every man has been born”)
Self-reference	When a proposition refers to itself, creating paradoxes (like “This sentence is false”)
Impetus	An internal force transmitted to a moving object that keeps it moving — Buridan’s way of explaining projectile motion
Insolubile	A puzzle that seems impossible to solve, especially a self-referential paradox
Intellectualism	The view that the will always follows what the intellect judges to be good
Voluntarism	The view that the will can sometimes act independently of the intellect’s judgment

Key People

John Buridan (c. 1300–c. 1358) — A master of arts at the University of Paris who spent his whole career teaching logic and philosophy, and whose ideas about choice were later parodied as “Buridan’s Ass.”
Aristotle (384–322 BCE) — The ancient Greek philosopher whose works formed the backbone of medieval education; Buridan spent his career explaining and sometimes disagreeing with him.
William of Ockham (c. 1287–1347) — A Franciscan philosopher known for “Ockham’s Razor” (don’t multiply entities unnecessarily); Buridan agreed with some of his ideas but disagreed about whether quantities are real things.
Thomas Aquinas (1225–1274) — A Dominican theologian who argued that the will always follows the intellect; Buridan’s view of choice was closer to this than he let on.
Duns Scotus (c. 1266–1308) — A Franciscan philosopher who argued that the will can act independently of the intellect; Buridan borrowed some of his vocabulary.

Things to Think About

Buridan’s Ass — The donkey story isn’t actually Buridan’s, but the puzzle is real. Have you ever been unable to choose between two equally good options? What did you do? Is “deferring and thinking more” always possible? What happens when you really do have to choose, right now?
Self-reference — “This sentence is false” seems like a game, but it points to a real problem. Can you think of other examples where something refers to itself in a way that creates confusion? (Hint: think about signs that say “ignore this sign,” or someone who says “I always lie.”)
Language and reality — Buridan thought many philosophical problems came from misreading language. Can you think of an argument you’ve heard that might be confused by taking words too literally? For example, someone says “the school thinks we need more homework” — does the school actually think anything, or is that just a shortcut for what some people at the school believe?
Trusting your senses — Buridan said we can trust our senses most of the time, even though God could theoretically deceive us. But modern technology can deceive us too: deepfakes, virtual reality, illusions. How do you decide what to trust? Is there a way to be absolutely certain about anything you perceive?

Where This Shows Up

Artificial intelligence and decision-making — The “Buridan’s Ass” problem appears in robotics when an AI has to choose between equally good options and gets stuck in a loop. Programmers have to build in tie-breaking rules.
Fake news and misinformation — Buridan’s approach to language — always asking what someone means rather than just what the words literally say — is relevant to understanding misleading headlines and manipulated content.
Psychology of choice — Psychologists study “choice paralysis” and “analysis paralysis,” which are basically the human version of the donkey problem. Too many options can freeze us.
Logic and computer programming — Self-reference creates real problems in computer science. The Liar Paradox is related to the “halting problem,” which asks whether you can write a program that determines whether other programs will run forever or stop. (Spoiler: you can’t.)