What Is the Gettier Problem?

Epistemology is a branch of philosophy that studies the nature of knowledge. Going back to Plato’s Theaetetus, a very common view says knowledge is justified true belief. But in the mid-twentieth century the philosopher Edmund Gettier challenged this account. He argues that someone can have a belief that is true and justified, but still not have knowledge because his belief is still true only by luck. 

The view that knowledge is justified true belief is often called the ‘tripartite’ account of knowledge. This is because it has three parts: belief, truth and justification. The roles belief and truth play in an account of knowledge are easy to see. 

Imagine John says he knows China is in East Asia but he refuses to believe it. It is very difficult to see how John’s position is coherent. How can he say he knows this but does not believe it? Belief appears to be necessary for knowledge on pain of incoherence. What about truth? Imagine John revises his position and says he believes and knows that China is a country in Europe. He has resolved the first problem: he no longer claims to know something he does not believe. But he now has another problem: what he believes (and claims to know) is false. The lesson is that knowledge is factive: John has knowledge only if what he believes is true. 

The Justification Condition is Critical to the Gettier Problem

Again, it seems intuitive that John does not know China is in East Asia. He believes this, it is true, but he has no justification—no reason or evidence—for believing it. The lesson is that knowledge requires belief, truth and justification. Otherwise one can have a belief that is true only by luck. John knowing China is in East Asia suggests that he’s ‘tethered’ to this fact in a way that eliminates merely luckily true belief. He has justification or reason to believe it, something that grounds his belief as more than a lucky guess. 

So we have reason to think the tripartite account of knowledge is on the right track: there is no instance of knowledge without belief, truth and justification. These three elements are therefore plausibly necessary for knowledge. But are they sufficient? Is it the case that every time John has a justified true belief he also has knowledge? 

The Gettier problem says ‘no’. 

Imagine John revises his position again and offers evidence for his belief that China is in East Asia. He shows you what appears to be a reliable map that clearly labels as ‘China’ a large landmass on the eastern side of the Asian continent. So he now believes this, it is true, and he has justification for his belief. Does he also know it? The Gettier problem says he doesn’t. Even though John has a justified true belief, his justification (in this case) does not eliminate lucky true belief.

Let’s see why. 

Justification Does Not Always Rule Out Lucky True Belief

Imagine the map John shows you is actually defective. Rather than being drafted by a reliable cartographer, it was drafted by a young child who knew only of the seven continents but neither where each is located nor what countries are in each. The child simply guesses the locations of the continents and their respective countries and, as it turns out, guesses correctly. By John’s lights, however, the map appears as reliable as any other. He has no reason to believe it is defective. So he seems justified in believing on its basis that China is in East Asia. 

The Gettier problem says that even though John a justified true belief that China is in East Asia, he does not have knowledge because his justification does not rule out the possibility that his belief is only luckily true. Had the child not correctly guessed the location of China, his map would have been deceiving and John’s belief would have been false. 

Scenarios like these sound far-fetched. But the lesson to take away is this: the tripartite account of knowledge does not rule out epistemic luck—lucky true belief—because it is possible to be justified in truly believing something without being ‘tethered’ to the fact that makes this belief true. John is plausibly justified on the basis of an accurate map in believing China is in East Asia. But this map’s accuracy was, unbeknownst to John, a mere fluke. 

So either the justification condition in the tripartite account of knowledge must be strengthened to eliminate misleading evidence—a requirement that many find too strong—or the tripartite account of knowledge is false.