Two Generals’ Problem

What is the Two Generals’ Problem?

The Two Generals’ Problem is like a puzzle from a story about two leaders who need to make the same plan without being able to talk directly. Instead, they send messages, but because these messages might get lost or caught by an enemy, they can never be completely sure the other one got the plan. It’s a big question that makes people think about how we can be certain of something when the way we communicate isn’t perfect.

Here’s another way to picture it: imagine trying to play a game with a friend in another room by passing notes under the door, but you can’t be sure if all the notes get through. You both need to agree on the next move in the game, but without knowing if the other has read your note, you keep sending more and more notes. This is the kind of problem computer scientists look at when they want to make computers talk to each other in a way that they can be sure they understand each other, even when some of their ‘notes’ disappear.

Key Arguments

  • The Problem of Trust: This problem makes us question if and how we can build trust when the way we get information is unreliable. If you can’t be sure your friend received your note for the game, how can you trust that they are ready to make the next move?
  • Uncertainty in Communication: If you send a note back to your friend saying you got their message, but they don’t know you got it, you’re stuck wondering again. This endless loop of trying to make sure everyone is on the same page shows how hard it is to be completely sure in a world where messages might not make it through.
  • Infinite Regression: Every time you try to confirm that a message was received, you actually need another confirmation. It’s like a never-ending staircase of confirmations that makes it impossible to reach the top and say, “Okay, now we’re ready!”

Answer or Resolution

The Two Generals’ Problem doesn’t have a clear answer or solution. It’s a puzzle that shows us the limits of what we can do when we can’t depend on our messages always getting through. No matter how many times the generals (or you and your friend passing notes) try to confirm the plan, there’s never a moment where both can be 100% sure the other is ready. This is why people who make computer systems and networks have to think of new ways to make decisions when the information isn’t perfectly reliable.

Major Criticism

Some people say that the Two Generals’ Problem is just an idea, not something that actually happens very often. They suggest that, in reality, our systems are usually reliable enough that we don’t need to worry too much about the problem. However, this example is still useful for understanding the kinds of problems that can come up in computer science, even if it’s not something we need to solve every day.

Practical Applications

Even though it’s a theory, the Two Generals’ Problem helps us understand real problems in computer science. When computers in different places need to work together but the messages they send could disappear or get ruined, we need to create systems that can handle that uncertainty.

  • Blockchain Technology: Blockchains use a special rule called Proof of Work to make sure all the computers (‘generals’) agree on what’s happening (‘the battle plan’). It’s like making sure everyone agrees on what move to make in the game, even if not all the notes get through.
  • Byzantine Fault Tolerance (BFT): This is another tricky problem where even some ‘generals’ could try to mess things up with bad messages. BFT is like a set of rules that help the game stay fair, even if someone is trying to cheat by passing false notes.
  • Computer Networking: The Internet uses something called TCP to make sure messages get from one computer to another, even though the Internet isn’t perfect. It doesn’t solve the Two Generals’ Problem, but it makes it less of a worry so that we can still play our game online, with only a very small chance of messages disappearing.


The Two Generals’ Problem is an important idea for times when it’s hard to trust the messages we send and receive. It doesn’t give us a straight answer, but it teaches us to think about how we can make decisions when things aren’t perfect.

Even though we can’t be 100% certain in some cases, this problem has led to new ways of making sure our digital world works pretty well even when communication isn’t perfect. It’s important because it has inspired better ways to make computers and networks more reliable and secure. So, even if we can’t beat the Two Generals’ Problem, we’ve learned from it and made our ‘digital generals’ smarter at making plans together.

Why is it Important

The Two Generals’ Problem might seem like just an interesting story, but it has a big impact on our everyday lives. When you send a message to a friend or when you buy something online, you are depending on technology that needs to be reliable. The solutions created for problems like this are what make those everyday actions possible without us even thinking about it.

For example, if you’re playing an online game, you expect your moves to be shared with others seamlessly. The foundations for ensuring this smooth communication come from understanding and solving complex issues like the Two Generals’ Problem. Banks, online stores, and even social media all rely on the safety and reliability of message-sharing systems that were developed because of these theoretical problems. This means that the behind-the-scenes work influenced by the Two Generals’ Problem is making sure that when you click “send” or “buy,” the digital world is listening and responding correctly.

Related Topics

  • Consensus Algorithms: These are rules used by computer systems to reach agreement on a single data value or a single state of the network among distributed processes or systems. They are crucial in making sure all parts of a system agree, much like the ‘generals’ need to agree on a plan of attack.
  • Reliable Messaging: This is about making sure messages get to where they’re supposed to go, even if there are problems like a bad internet connection or a power outage. It’s like having a back-up plan when passing notes doesn’t work.
  • Cryptographic Protocols: These are methods that use math and secret codes to secure communication. They make it so that even if someone catches a ‘message,’ they can’t understand it unless they’re supposed to. Think of this as writing your notes in a secret code that only your friend can read.