Is Justified True Belief Knowledge?
Edmund Gettier
About Is Justified True Belief Knowledge?
Edmund Gettier’s 1963 paper is one of those rare philosophy articles that’s short, punchy, and absolutely game-changing. Before this, most philosophers thought they had a pretty good handle on what “knowledge” is: if you believe something, it’s true, and you have good reasons (justification) for believing it—boom, that’s knowledge. End of story, right?
Wrong, says Gettier.
In just a few pages, Gettier showed that this classic definition—known as the “Justified True Belief” (JTB) theory—wasn’t as airtight as everyone thought. He introduced two little thought experiments (now called “Gettier cases”) that totally blew it up. These stories show people who have justified true beliefs… that still don’t seem like actual knowledge. Why? Because they got lucky.
Imagine this: you believe your friend owns a Ford because you’ve seen him drive one for years. That belief is true—he does own a Ford. But your justification actually comes from misleading evidence (like maybe he sold it yesterday and rented one that looks the same). So technically, your belief is true and justified… but do you really know it? Gettier says: nope.
Gettier’s paper is famous for being short and devastating. In just a couple of pages, he broke a definition of knowledge that had lasted over 2,000 years—going all the way back to Plato. And ever since, philosophers have been scrambling to figure out what knowledge really is.
Before you read
You probably think you know stuff—like your name, or what you had for breakfast. And if you believe something, it’s true, and you have a good reason for it… well, that feels like knowing, right? For centuries, philosophers agreed with you.
But Edmund Gettier came along and was like, “Hold up. What if you’re right by accident?” That’s the twist. His examples show that someone can have all the ingredients of knowledge—belief, truth, and justification—and still somehow miss the mark. It’s like baking a cake with the right recipe but ending up with a pie by accident.
So before you dive in, ask yourself: is being correct enough? Or does knowledge need to be correct in the right way?
Guiding Questions
- What is the traditional definition of knowledge that Gettier challenges?
- What’s the twist in Gettier’s “Gettier cases” that makes them so surprising?
- Why does Gettier think that justified true belief isn’t enough for knowledge?
- How do Gettier’s examples change the way we think about what it means to know something?
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