Fitch’s Paradox of Knowability

What is Fitch’s Paradox of Knowability?

Fitch’s Paradox of Knowability is a puzzle about what we can know. Imagine that there is a huge library with all the facts about the universe. Some books are read by people, and some are not. Now, suppose someone claimed that even the unread books could be read – every single truth in the library was available for someone to eventually learn. But here’s the twist: if every truth could be known, then why are there still unread books? Shouldn’t they all be read by now if they can be known? The paradox comes from this confusing situation. We expect some books to be left unread, but the claim that every truth can be known seems to say they should all be read. This is what creates the puzzle: the belief that every fact can be discovered conflicts with the fact that some truths are still unknown.

Fitch’s Paradox of Knowability is like saying that every secret can be figured out, but then finding out that if this were true, there wouldn’t be any secrets left. But there are still secrets, which makes it a riddle.

It’s like a math problem that doesn’t add up. You have two ideas that seem good on their own — one, that every true thing can be known, and two, that there are true things nobody knows. Yet when you put them together, they don’t work out, because they suggest if one thing is correct, the other one can’t be.


The paradox gets its name from Frederic Fitch, who first described this complex problem in 1963. He wanted to show what happens when you take the thought “every truth is possible to know” to its extreme conclusion. Fitch made a logical proof like a math formula, but he used ideas instead of numbers. He found that this friendly thought led to a strange result: if every true thing could be known, this would mean that every true thing was already known, which is clearly not true because we’re always discovering new things.

Key Arguments

  • The Knowability Thesis: This is the thought that for any truth, it is possible for someone to know it. We like this idea because it gives hope that with enough time or smart thinking, no truth is out of reach.
  • Verifiability Principle: This idea is connected to the Knowability Thesis. It says that the value of a statement comes from whether we can check if it’s true or false. If we can’t check it, then the statement doesn’t really say anything. The paradox challenges this idea.
  • Fitch’s Argument: Fitch used logic to show that if every truth could be known, all truths would actually be known already. But we know that’s not right because every day, people are finding out new things.

Answer or Resolution (if any)

So far, no one has found a clear solution to this paradox that everyone agrees on. Some people have suggested maybe not all truths are meant to be known. Others think that maybe we’re just confused about what ‘truth’ and ‘knowability’ really mean, and that’s why it seems like a contradiction.

Major Criticism

One of the big criticisms is that the paradox mixes up the possibility of knowing something with actually knowing it. They say just because something can be known doesn’t mean it will be. They also think that maybe the paradox comes from trying to use a certain type of logic, modal logic, in a way it’s not supposed to be used when talking about knowledge and truth.

Practical Applications

The paradox might sound like it is just for people who like to think about tricky ideas, but it actually comes up in real life:

  • Philosophy of Science: It makes scientists think about whether there could be things they can’t ever know, no matter how hard they try.
  • Information Theory: In a world where we think any information can be found online, the paradox pushes us to question whether there might be limits to what we can find out.
  • Security and Privacy: If being able to know something means it will definitely be known, then we really have to think about keeping private things safe because the paradox suggests there is no guaranteed privacy.

Related Topics

  • Epistemology: This is the study of knowledge. It looks at what knowledge is, how we get it, and how we know we have it. Fitch’s Paradox fits right in because it’s all about the limits of what can be known.
  • Modal Logic: A type of logic that talks about what’s possible and necessary. The paradox uses this kind of thinking to create its puzzle.
  • Anti-Realism: This is the idea that the world is not composed of things that exist independently of our thoughts and perceptions. The paradox supports anti-realism by suggesting some truths might never be known.

Why is it Important?

It’s easy to think that Fitch’s Paradox is just for brainy types who like to talk about deep things. But it actually affects all of us. Every time we search for answers, learn new things, or keep secrets, we’re dealing with the ideas at the center of the paradox. It makes us wonder about the limits of what humans can understand. This is important because it affects how we learn and grow. It makes us ask: Are there some things we’re just not meant to know? This isn’t just a thought experiment; it’s about how we live our lives and how we deal with not knowing everything.


In summary, Fitch’s Paradox of Knowability gets us into a twisty problem about truth and knowledge. On one hand, we have the hopeful idea that all truths are possible to know. On the other, we hit the wall of the unknown – truths no one has discovered yet. This isn’t just a puzzle on paper. It pops up in science, information, and even in personal privacy. Thinking about this paradox gives our brains a workout and reminds us of a big question: What does it really mean to know something? Whether we’re trying to solve the paradox, criticize it, or find it in real life, it keeps us on our toes and thinking about the mysteries of knowing and the unknown.