The Man Who Changed His Mind: Abner of Burgos and the Problem of Free Will

Imagine you’re walking home from school, and you see a kid drop a quarter. You could pick it up and keep it. Nobody would know. But you don’t. You walk past.

Did you choose to leave the quarter? It feels like you did. But what if every decision you’ve ever made—and will ever make—was already decided before you were born? What if your choice to leave the quarter was as inevitable as the sun setting?

This is the problem of free will, and it’s one of the oldest, weirdest puzzles in philosophy. But here’s the twist: the person who pushed this problem further than almost anyone before him was a 14th-century Jewish philosopher who converted to Christianity, argued with his former students, and believed that the Eucharist (the bread and wine used in Christian church services) could be explained by physics.

His name was Abner of Burgos, and his story is strange, uncomfortable, and fascinating.

A Rain of Crosses

Abner was born around 1260 in Burgos, a city in what is now Spain. He was Jewish, a rabbi, and a philosopher. He ran a school, traded books, and probably worked as a doctor. He was deeply embedded in the Jewish philosophical traditions of his time.

Then something happened.

In 1295, a rumor spread through the Jewish community of Avila, a nearby city. A false messiah had appeared. People rushed outside the city walls to greet him. Instead of a messiah, they got a rain of crosses—crosses that fell from the sky and stuck to their clothes. This was, understandably, confusing.

Some of the witnesses went to Abner for advice. He didn’t know what to tell them. The event planted a doubt in his mind. If Judaism was true, why were the Jewish people still in exile? Why hadn’t the messiah come? And what if those crosses meant something?

For twenty-two years, Abner wrestled with this doubt. Then he had a dream. A man appeared to him and said he would be a “teacher of righteousness”—someone who would lead his people out of exile. Three years later, he had another dream. Same man, same message—but this time the man was wearing robes covered in crosses.

Abner converted to Christianity around 1320. He was about sixty years old.

After his conversion, he didn’t just quietly practice his new religion. He wrote books arguing that Christianity was true and Judaism was mistaken. He debated with rabbis. He even helped get a Jewish prayer banned—the birkat ha-minim, a prayer against heretics and apostates—because it targeted people like him.

But here’s what makes Abner interesting to philosophers: he didn’t just switch teams. He built an entire system of thought that connected free will, physics, and theology. And his ideas, even the ones that came from his Christian period, were deeply Jewish in their sources and concerns. He was still arguing with Jewish philosophers, using Jewish texts, decades after he left Judaism.

The Wax and the Will

Let’s get to the big question: do we have free will?

Abner’s answer was pretty much no.

But he didn’t get there by saying “God controls everything,” which is the simple version. He built a more interesting argument.

Abner said that the nature of will is to be able to choose between opposites. That capacity—the ability to choose—is eternal and timeless. But here’s the catch: every actual choice you make, every real decision in time, is determined by causes. You can’t just decide anything at any moment. Your decisions are shaped by your desires, your history, your environment, everything.

Abner used a cool analogy: the will is like wax. Wax has the nature to take any shape. That’s what wax is. But the actual shape it takes at any moment depends entirely on what causes are acting on it—the heat, the mold, the pressure. The wax doesn’t choose its shape. It just takes whatever shape the causes give it.

So for Abner, there are no real accidents. If you trip and fall, it feels random. But from the perspective of all the causes in the universe—the crack in the sidewalk, the way your shoe hit the ground, the distraction in your mind—your fall was inevitable. “Accident” is just a name we give to things whose causes we can’t see.

This leads to two big problems, and Abner knew it.

Problem one: If we don’t have free will, why does God give us commandments? Why tell people to do things they can’t actually choose to do?

Problem two: How can people be rewarded or punished for actions they had no control over?

Abner’s answers are pretty radical.

For problem two: punishment isn’t God getting angry at you. Punishment is just the natural consequence of bad actions. If you put your hand in a fire, you get burned. That’s not a special punishment—it’s just what fire does to hands. Same with moral badness. Bad actions are naturally bad for you. The bad consequences follow automatically.

For problem one: the Torah (and by extension, God’s commandments) is a cause in the world, just like anything else. It influences people toward good, the way medicine influences your body toward health. Abner compared it to a father making his son take medicine. The son might not choose freely to take it, but the medicine works anyway.

This is a cold, mechanical view of the universe. Everything happens because it had to happen. But Abner thought this was actually the only way to make sense of God’s knowledge. If God knows everything that will happen, and God can’t be wrong, then everything that happens must happen the way God knows it will. You can’t have a universe where God is all-knowing and people have real, genuine choices that could go either way.

The Body That Fills the Universe

Abner’s determinism connected to his physics, which connected to his theology. He was building one complete picture of reality.

Most philosophers in his time followed Aristotle, who said that every physical body has certain necessary properties: size, shape, weight, location. You can’t have a body without these. But Abner disagreed.

He thought you could strip away all the properties of a body—its size, its shape, its weight, even its location—and still have something there. That something was pure matter, pure existence, with no limits. And this unlimited matter was everywhere, all at once.

Why did Abner care about this? Because of the Eucharist.

In Christian theology, the bread and wine of communion become the body and blood of Jesus. But how? There were scientific objections: How can one body be in multiple places at once? How can bread become a human body without changing appearance? How can Jesus’ body be eaten without being destroyed?

Abner’s answer: Jesus’ body is that unlimited, property-less matter. It’s everywhere. It fills the universe. So when the bread becomes Jesus’ body, it doesn’t have to travel or change shape. It was already there. The bread just gets stripped of its normal properties, revealing the underlying divine matter that was always present.

This is weird, but it’s also brilliant. Abner took a theological doctrine and used it to argue against the dominant physics of his time. He was saying: Aristotle was wrong about matter. Matter doesn’t have to have properties. And here’s the proof: the Eucharist works.

Why This Still Matters

You might be thinking: okay, this is interesting history, but what does it have to do with me?

Here’s the thing. The problem Abner was wrestling with—determinism vs. free will—is still alive. It hasn’t gone away. In fact, it’s gotten more intense.

Neuroscience is showing that your brain makes decisions before you’re consciously aware of choosing. Genetics shapes your personality. Your environment shapes your beliefs. The more we learn about how the mind works, the harder it gets to find a place for free will.

And Abner’s solution—that we don’t have free will, but we should still act as if we do—is actually similar to what some modern philosophers and scientists say. They argue that we can’t live without believing in free will, even if it’s an illusion. We need to hold people responsible. We need to feel like our choices matter. The feeling of choosing might be a useful fiction.

But not everyone agrees. Some philosophers say free will is real, and any scientific theory that denies it must be wrong. Some say free will exists but it’s nothing like what we think it is. Some say the whole question is confused and we’re asking it wrong.

Abner’s story also shows something uncomfortable: people can change their minds about the deepest things, and that change can have real consequences. His conversion wasn’t just a personal choice. It led him to attack his former community, to argue against Jewish beliefs, to help ban a prayer. His philosophy and his life were tangled together in ways that are hard to untangle.

Does that make his ideas wrong? Not necessarily. But it means we have to think about where ideas come from and what they’re used for.

What Philosophers Still Argue About

Here’s where it gets really interesting. Abner’s determinism wasn’t just a weird historical footnote. It influenced later philosophers. Hasdai Crescas, a Jewish philosopher who lived about fifty years after Abner, borrowed many of Abner’s arguments—even though Crescas was writing against Christianity. And Crescas influenced Spinoza, who is one of the most important philosophers of the modern era. Spinoza also believed in a kind of determinism, and he was also exiled from his Jewish community for his ideas.

So the thread runs: Abner → Crescas → Spinoza → modern philosophy.

And the debate continues. Today, philosophers ask: If our actions are determined by prior causes, can we be morally responsible? Is punishment justified if people couldn’t have done otherwise? Does it even make sense to say “you should have done something different” if the universe made it impossible?

Some philosophers say yes, we can still hold people responsible—because responsibility isn’t about free will, it’s about responding to reasons. If you can understand why something was wrong, and if you could have responded to that reason, you’re responsible, even if your response was determined.

Others say no. If determinism is true, then no one truly deserves punishment or praise. We might still need to punish people to protect society, but it wouldn’t be fair in the deep sense.

And some philosophers think the whole debate is built on a mistake. They say we shouldn’t think of free will as a magical power to defy causality. Free will is just the ability to act according to your own desires and reasons, without being forced by someone else. And that kind of free will is perfectly compatible with determinism.

Nobody has won this argument. It’s been going on for centuries, and it shows no signs of ending. That’s part of what makes it fascinating. You’re being invited into a conversation that has no final answer—but that matters deeply for how we live our lives.

Key Terms

Term	What it does in this debate
Determinism	The view that every event, including human decisions, is caused by prior events and could not have happened otherwise
Free will	The capacity to make genuine choices that aren’t forced by prior causes
Essence	The fundamental nature or “whatness” of a thing—what makes it what it is
Accident	A property that a thing has but could lack without ceasing to be what it is (like the color of a ball)
Prime matter	The basic stuff of the universe, before it takes on any specific form or properties

Key People

Abner of Burgos (c. 1260–1347): A Jewish rabbi and philosopher who converted to Christianity and developed a radical deterministic philosophy that influenced later thinkers.
Hasdai Crescas (c. 1340–1410): A Jewish philosopher who opposed Christianity but borrowed many of Abner’s arguments about determinism and physics.
Baruch Spinoza (1632–1677): A Jewish philosopher who was excommunicated from his community for his ideas and who developed a deterministic system influenced by Crescas and, indirectly, by Abner.

Things to Think About

If you found out that determinism was true—that every choice you’ll ever make is already forced—would that change how you live? Should it?
Abner argued that punishment is just the natural consequence of bad actions, not something God or society chooses to impose. Do you think this makes punishment more fair, or does it dodge the real question?
When Abner converted to Christianity, he used his philosophical skills to attack his former community. Does the fact that an idea is used to harm people make that idea less likely to be true? Or are ideas independent of how they’re used?
The problem of free will connects to science today—neuroscience, genetics, psychology. If a scientist could prove determinism is true, would that settle the philosophical debate? Or is there something about free will that science can’t touch?

Where This Shows Up

In court: Legal systems assume people are responsible for their actions. But if someone’s brain is damaged, or if they were raised in terrible conditions, do we hold them less responsible? The free will debate shows up in every courtroom.
In school: When a teacher says “you should have done your homework,” they’re assuming you could have done otherwise. If determinism is true, is that assumption fair?
In video games: When you make a choice in a game, was it really your choice, or was it determined by the game’s code? The experience of choosing in a game feels real—but the outcome was always going to happen. Sound familiar?
In arguments about punishment: Some people think punishment should be about making society safer (deterrence). Others think it should be about giving people what they deserve. These two views rely on different assumptions about free will.