Shattering the Definition of Knowledge: Gettier Problems and the JTB Analysis

For most of philosophical history, knowledge was defined by the 'Justified True Belief' (JTB) account. This tripartite theory holds that for someone to know a proposition, they must believe it, it must be true, and they must have adequate justification for their belief. This definition seemed intuitive and comprehensive, successfully distinguishing knowledge from mere opinion or lucky guesses for over 2,000 years. This long-standing consensus was shattered in 1963 by Edmund Gettier's paper, "Is Justified True Belief Knowledge?". Gettier constructed clever counterexamples demonstrating that the JTB conditions are not sufficient for knowledge. In a typical 'Gettier problem', a person forms a belief based on strong but ultimately misleading evidence. While their initial belief is false, they use it to deduce a second belief that, by sheer coincidence, happens to be true. The person therefore has a justified true belief, yet we would not consider it knowledge because it is true only by luck. The justification is fundamentally disconnected from the state of affairs that makes the belief true. The Gettier problem exposed a critical flaw in the traditional understanding of knowledge, highlighting the role of 'epistemic luck'. In the decades since, epistemologists have worked to 'fix' the JTB account, proposing various fourth conditions—such as the absence of false premises ('no false lemmas') or the requirement of a reliable belief-forming process. However, no single solution has gained universal acceptance, and Gettier's challenge remains a central and defining problem in modern epistemology.

1. The Traditional Account of Knowledge: Justified True Belief (JTB)

For centuries, dating back to Plato's dialogue Theaetetus, philosophers have sought a precise definition of knowledge. What does it mean to know something, as opposed to merely believing it or guessing correctly? The traditional and most widely accepted answer was the Justified True Belief (JTB) account. According to this tripartite analysis, knowledge is defined as a belief that is both true and adequately justified.

To say that a subject (S) knows a proposition (P), the following three conditions must be met:

1. Truth Condition: The proposition P must be true. You cannot know something that is false. For example, you cannot know that the Earth is flat, even if you sincerely believe it and have what you consider to be reasons for that belief. Knowledge is factive; it must connect with reality.

1. Belief Condition: S must believe that P is true. Knowledge is a mental state that requires personal assent. If you don't actually believe that Paris is the capital of France, you cannot be said to know it, even if you can state the fact correctly on a test.

1. Justification Condition: S must be justified in believing that P is true. This is the crucial condition that separates knowledge from a lucky guess. If you randomly guess the winning lottery numbers, you had a true belief, but you didn't know they would win because you had no justification. Justification can come from various sources: empirical evidence, logical deduction, reliable testimony, memory, etc.

For over two millennia, the JTB account was the bedrock of epistemology, seeming both intuitive and robust. It appeared to successfully distinguish knowledge from all other cognitive states.

2. Enter Edmund Gettier: The 1963 Revolution

In 1963, a philosopher named Edmund Gettier published a brief, three-page paper titled "Is Justified True Belief Knowledge?" that would fundamentally and permanently alter the field of epistemology. Gettier's paper did not argue that any of the JTB conditions were unnecessary; instead, he argued that they were not sufficient. He proposed ingenious counterexamples—now known as Gettier problems—in which a person could have a justified true belief, yet we would intuitively deny that they possess knowledge.

Gettier's argument rests on two key principles:

1. It is possible for a person to be justified in believing a proposition that is, in fact, false.
2. If a person is justified in believing a proposition P, and P entails another proposition Q, and the person deduces Q from P and accepts Q as a result of this deduction, then the person is also justified in believing Q. (This is known as the principle of deductive closure for justification).

With these principles, Gettier constructed scenarios where justification and truth come apart in a surprising way.

3. Gettier's Classic Counterexamples

Case I: The Man with Ten Coins in His Pocket

Imagine two men, Smith and Jones, who have applied for the same job. Smith has strong evidence for the following belief:

• (a) Jones is the man who will get the job, and Jones has ten coins in his pocket.

Smith's justification for (a) is that the company president told him Jones would be selected, and he, Smith, had counted the coins in Jones's pocket a few minutes ago. From proposition (a), Smith validly infers:

• (b) The man who will get the job has ten coins in his pocket.

Now, let's introduce the twist. Unbeknownst to Smith, he himself will get the job, not Jones. And, also unbeknownst to him, he himself happens to have ten coins in his pocket.

Let's analyze Smith's belief in proposition (b) against the JTB criteria:

1. Is (b) true? Yes. The man who will get the job (Smith) does indeed have ten coins in his pocket.
2. Does Smith believe (b)? Yes. He inferred it from (a).
3. Is Smith justified in believing (b)? Yes. He has strong evidence for (a) and has logically deduced (b) from it.

Smith has a justified true belief in (b). However, would we say that Smith knows that the man who will get the job has ten coins in his pocket? The overwhelming intuition is no. His belief is true only because of an extraordinary coincidence—the number of coins in his own pocket, a fact he was unaware of. His justification was based on the coins in Jones's pocket, but Jones didn't get the job. The justification is fundamentally disconnected from the fact that makes the belief true.

Case II: Brown in Barcelona

Smith is justified in believing that his friend Jones owns a Ford. His justification is that he has always known Jones to own a Ford, has just seen Jones driving a Ford, and Jones just offered him a ride in his Ford. From this justified belief:

• (c) Jones owns a Ford.

Smith has another friend, Brown, and he has no idea where Brown is. He arbitrarily forms a new proposition using a logical disjunction (an "or" statement):

• (d) Either Jones owns a Ford, or Brown is in Barcelona.

Smith is justified in believing (d) because he derived it from (c), which he is justified in believing. Now, for the twist: Jones does not, in fact, own a Ford (he was driving a rental car). However, by sheer, dumb luck, Brown actually is in Barcelona.

Let's analyze Smith's belief in proposition (d) against the JTB criteria:

1. Is (d) true? Yes. A disjunction is true if at least one of its parts is true. While the first part is false, the second part ("Brown is in Barcelona") is true.
2. Does Smith believe (d)? Yes. He inferred it from (c).
3. Is Smith justified in believing (d)? Yes. His justification flows from his justified belief in (c).

Once again, Smith has a justified true belief that fails to be knowledge. His belief is true, but the reason it's true (Brown being in Barcelona) has nothing to do with his justification for holding the belief (his evidence about Jones's car).

4. The Core Problem and Its Aftermath: Epistemic Luck

Gettier problems reveal that the JTB account is flawed because it allows for a form of epistemic luck. In these cases, a belief is justified based on evidence that points towards the truth, but the belief ultimately turns out to be true for a completely different, coincidental reason. The causal chain that connects the evidence to the belief is broken and replaced by luck.

The publication of Gettier's paper launched a massive and ongoing project in epistemology to "solve" the Gettier problem. This has generally involved trying to add a fourth condition to the JTB analysis (a "JTB+X" theory) or replacing the justification condition altogether. Some proposed solutions include:

• The "No False Lemmas" Condition: This suggests that for a belief to be knowledge, the justification for it cannot rely on any false beliefs (or "false lemmas"). This would solve the classic Gettier cases, as Smith's justification relied on the false belief that "Jones will get the job" or "Jones owns a Ford."
• Reliabilism: This theory replaces the justification condition with the requirement that the belief must be produced by a reliable cognitive process (e.g., clear vision, sound logical reasoning, etc.).
• Causal Theories: These theories require an appropriate causal connection between the fact that makes the belief true and the subject's belief itself.

Despite these efforts, no single solution has been universally accepted, and philosophers continue to debate the precise nature and definition of knowledge, all thanks to a three-page paper that challenged two millennia of consensus.

Browse public study notes