What Must a Jew Believe? Joseph Albo’s Search for the Essentials

Imagine you’re arguing with someone who claims to be Jewish—except they deny that God exists. Or they say the Torah was written by humans, not revealed at Mount Sinai. Or they insist that there’s no reward or punishment for how people live. Are they still Jewish? Can you reject one of these ideas and still count as a believer? What makes someone a true member of a religion, anyway?

This wasn’t just a hypothetical question for Joseph Albo, a Jewish philosopher and rabbi who lived in Spain in the early 1400s. He was caught in a nightmare. The Catholic Church was pressuring Jews to convert to Christianity. Violent attacks on Jewish communities—especially the terrible pogroms of 1391—had killed many people and forced others to convert out of fear. Jewish communities were shrinking, confused, and scared. Some Jews were converting, and many others were arguing among themselves about what Judaism really required you to believe.

Albo wrote a book called Sefer ha-‘Ikkarim—“The Book of Principles”—to try to answer a question that felt urgent: What are the essential beliefs a person must hold to be a follower of divine law? If he could figure that out, he thought, he could show Jews what was worth defending and what wasn’t. Maybe he could stop the bleeding.

Three Basic Beliefs—Or Are They Enough?

Before Albo, the most famous list of Jewish principles came from Maimonides, a philosopher from about 150 years earlier. Maimonides had listed thirteen things every Jew must believe: that God exists, that God is one, that God has no body, that the Torah came from God, that the Messiah will come, that the dead will be resurrected, and so on.

Albo thought this was too many. Not because he disagreed with them—he probably accepted most of them—but because he thought Maimonides was mixing up two different kinds of beliefs. Some beliefs, Albo argued, are absolutely necessary for any religion that claims to come from God. Others are important but not that important. You could reject the less important ones and still be a believer. You’d be wrong, but you wouldn’t be a heretic.

So Albo boiled it down to three basic principles that he thought any “divine law” must have:

The existence of God.
The divine origin of the Torah (that God actually revealed it to humans).
Reward and punishment (that God notices what we do and responds).

If you deny any of these three, Albo said, you’ve stepped outside of Judaism entirely. But if you accept all three, you’re in—even if you get some other things wrong.

This sounds simpler, doesn’t it? But it’s actually more complicated than it looks, because Albo added two more layers.

Roots and Branches: A Tree of Belief

Albo pictured beliefs like a tree. The three principles were the trunk—they hold everything up. But from each principle grow roots, which are more specific beliefs that the principle needs in order to make sense. Then from the roots grow branches, which are important but not essential.

Here’s how it works. The first principle—that God exists—has four roots:

God is one
God has no body
God is not affected by time
God has no flaws

The second principle—that the Torah comes from God—has three roots:

God knows everything
God can communicate with humans (prophecy is real)
The person who brought the message (Moses) was genuinely sent by God

The third principle—reward and punishment—has one root:

God watches over the world (divine providence)

So that’s three principles and eight roots. If you deny any of these, you’re out. That’s eleven beliefs that Albo thought were truly fundamental.

Then come the branches—six of them, including things like:

The world was created out of nothing
Moses was the greatest prophet
The Torah will never be replaced or changed
The dead will be resurrected
The Messiah will come

Denying a branch, Albo said, is a sin. You should repent and try to learn better. But it’s not heresy. You’re still a believer.

Why does this distinction matter? Because Albo was trying to draw a line somewhere. If you make the list of required beliefs too long, you’ll kick people out for small mistakes. If you make it too short, you lose what’s special about your religion. Albo wanted to find the real essentials—the beliefs without which the whole thing falls apart.

Natural Law, Conventional Law, Divine Law

Albo’s three principles aren’t just about Judaism. He thought they applied to any religion that claims to come from God. And here’s where his thinking gets interesting.

Albo distinguished three kinds of law. Natural law is the basic moral code that any reasonable person can figure out: don’t murder, don’t steal, be fair. You don’t need God to tell you this. Conventional law is what humans invent to run society: traffic rules, tax systems, school policies. These change depending on where you live and what people agree on.

Divine law is different. It comes directly from God through a prophet or messenger. Judaism was divine law; so, Albo thought, were Christianity and Islam—though he believed only Judaism was the true divine law. And here’s the key: a true divine law has to contain Albo’s three principles. If a religion claims to be from God but denies God’s existence, or says God didn’t really reveal it, or teaches that God doesn’t care about how people live—then it’s proven false by its own contradictions.

This was a weapon in Albo’s fight against Christianity. Christians claimed their religion came from God. But Albo argued that some Christian beliefs (like the Trinity, which he thought conflicted with God’s unity) contradicted the necessary principles of any divine law. So Christianity couldn’t be true divine law, even if it claimed to be.

The Trouble With Albo’s System

Here’s a problem, and philosophers have noticed it: How do you know which beliefs are really the essential ones? Albo said the three principles are “derived necessarily from the term ‘divine law.’” But that’s just his opinion. Someone else—Maimonides, for example—might look at the same term and see thirteen principles. Another philosopher might see only one: “God exists.” How do you decide?

Albo’s answer seems to be: Think about what a system of law from God needs to have. A law from God needs a God who exists. It needs that law to actually come from God. And it needs that law to matter—to have consequences. Albo thought these follow logically from the concept itself. But “logically” here means “to Albo’s way of thinking.” Not everyone agrees.

There’s another problem. Albo’s book is full of contradictions. In some places he says one thing; in other places he says the opposite. For a long time, scholars thought this just meant Albo wasn’t a very careful thinker—he copied from different sources without worrying about consistency. But more recently, some scholars have suggested a different explanation: maybe Albo was writing in code.

Did Albo Hide His Real Beliefs?

This is a fascinating possibility. Some scholars now argue that Albo wrote two layers into his book. The surface layer—the “exoteric” meaning—is what any ordinary reader would see. But underneath, there’s a hidden or “esoteric” layer that slips in ideas Albo didn’t want to state openly.

Why would he do this? Because the times were dangerous. If Albo expressed certain ideas too directly, he might be attacked by conservative Jews who thought philosophy was corrupting. Or he might give ammunition to Christians who were looking for reasons to condemn Judaism. So, the theory goes, Albo sometimes said the safe, orthodox thing on the surface, while planting hints for careful readers about what he really thought.

For example, did Albo believe the world was created out of nothing? He listed that as a “branch” belief—important but not essential. But in other parts of the book, he seems to suggest that matter might be eternal, which is a very different idea. Which one did he actually hold? We can’t be sure. Maybe both. Maybe neither. Maybe the contradictions are intentional.

This is still a live debate among scholars. Is Albo an eclectic writer who just wasn’t very systematic? Or is he a careful esoteric writer hiding his true views? The answer matters, because it changes how we interpret everything he says.

Why It Still Matters

Albo was trying to solve a problem that every community faces: What are the rules for membership? Who’s in, and who’s out? And how do you know?

Judaism doesn’t have a pope or a central authority that can settle these questions. So philosophers like Albo tried to use reason to figure out where the boundaries are. His three principles were an attempt to say: Here’s the minimum. Everything else is important but not essential.

But that raises another question: If you reduce a religion to its bare minimum, what’s left? Is a person who believes only these three things really practicing the same religion as someone who observes all the commandments, studies the texts deeply, and lives a life of devotion? Albo thought yes—they could both be genuine followers of divine law. But he also thought the person who believes more is better off.

The tension Albo wrestled with—between making the requirements too strict or too loose—isn’t just a medieval problem. It’s a problem for any group that has beliefs. Whether it’s a religion, a political movement, or even a club, someone has to decide: What do you absolutely have to believe to belong? And who gets to make that call?

Appendices

Key Terms

Term	Job in the Debate
Principles	The three essential beliefs (existence of God, divine origin of Torah, reward and punishment) that any divine law must have
Roots	The eight more specific beliefs that make the principles meaningful; denying any root is heresy
Branches	Six important beliefs that followers should accept but that aren’t required for membership; denying them is a sin but not heresy
Divine law	A system of laws that comes directly from God through revelation (like Judaism)
Natural law	Basic moral rules that any human can figure out using reason alone
Conventional law	Human-made laws that organize society (like traffic rules or school policies)
Esoteric writing	A style where the author hides their true views beneath a safe surface meaning, so only careful readers can find them

Key People

Joseph Albo — A Jewish rabbi and philosopher in 1400s Spain who wrote Sefer ha-‘Ikkarim to figure out the essential beliefs of Judaism during a time of persecution and forced conversion.
Maimonides — A famous Jewish philosopher from about 150 years before Albo who listed thirteen principles of Jewish faith; Albo thought this list was too long and mixed up essential with non-essential beliefs.

Things to Think About

Albo says denying a “branch” belief is less serious than denying a “principle” or “root.” But who decides which is which? Could there be a fair way to settle that disagreement without a single authority figure?
If a person accepts all three of Albo’s principles but lives a completely immoral life—lying, cheating, hurting others—are they really a follower of divine law? Does believing the right things matter more than acting the right way?
Albo thought Christianity couldn’t be true divine law because it contradicted some of his principles (especially the unity of God). But what if Albo was wrong about what Christianity actually teaches? How confident can you be that you’ve understood another religion correctly when you’re criticizing it?
If Albo really did write esoterically—hiding his true beliefs—then we can’t be sure what he actually thought about anything. Is that a problem for philosophy? If a philosopher can’t say clearly what they mean, does their work still count as philosophy?

Where This Shows Up

Religious communities today still debate who counts as a member. Some Orthodox Jewish groups don’t recognize conversions performed by other rabbis. Different Christian denominations disagree about what you must believe to be saved. Albo’s questions are still alive.
Political parties and activist groups also face these questions: “What do you have to believe to be a real feminist? A real Democrat? A real conservative?” The fight over minimum requirements happens everywhere.
Schools and clubs draw membership boundaries too. Can you be a real fan of a team if you don’t watch every game? Can you be part of a friend group if you miss the inside jokes? Albo’s framework of principles/roots/branches could apply to lots of groups, not just religions.