---
title: What is Knowledge?
section-id: epistemology
sort: 100
author: Prof. James Okafor
created: 2026-01-15 09:00
modified: 2026-02-20 11:00
language: en
description: The classical analysis of knowledge as justified true belief, and Gettier's challenge to it.
---

# What is Knowledge?

Epistemology is the philosophical study of knowledge: what it is, how we acquire it, and what its limits are. The first question—what is knowledge?—might seem too obvious to need asking. Surely we know what knowledge is: it is when you correctly believe something and can back it up. As it happens, making this precise is surprisingly difficult.

## The Classical Analysis

The traditional philosophical analysis of knowledge, often attributed to Plato's dialogue *Meno* and *Theaetetus*, is that knowledge is **justified true belief** (JTB). To know that *p*:

1. *p* must be **true**
2. You must **believe** that *p*
3. Your belief must be **justified**

Each condition seems necessary. You cannot know something false—if it turns out the earth is not round, you never knew it was round, you merely believed it. You cannot know something you do not believe—a detective who does not believe the suspect is guilty does not know the suspect is guilty, even if the suspect is. And belief alone is insufficient—a lucky guess is not knowledge.

For most of the twentieth century, this analysis was widely accepted. Then in 1963, Edmund Gettier published a three-page paper that changed the situation entirely.

## The Gettier Problem

Gettier showed that justified true belief is not sufficient for knowledge by constructing cases where all three conditions are met and yet we resist saying the person knows.

Here is a simplified version. Suppose you have strong evidence that your colleague Amara has a broken leg—you saw the X-ray, you heard the doctor’s diagnosis. You form the belief: ‘Someone in this building has a broken leg.’ As it happens, Amara does not have a broken leg; the X-ray was accidentally switched. But you have a broken leg—you just don’t know it yet.

In this case:
- Your belief (‘Someone in this building has a broken leg’) is **true**—you yourself have a broken leg
- You **believe** it
- You are **justified**—the X-ray and diagnosis are excellent evidence

But you do not know it. The truth of the belief has nothing to do with your justification; the two are connected only by coincidence.

Gettier cases reveal that knowledge requires not just that your belief is justified and true, but that the justification is appropriately connected to the truth.

## Responses to Gettier

### The No-False-Lemmas Approach
One early response held that Gettier cases always involve inference through a false intermediate belief (a ‘false lemma’). In the example, you infer from the false belief that Amara has a broken leg. If we add the condition that the justification must not pass through any false beliefs, we block the counterexample. Unfortunately, it is possible to construct Gettier cases that do not involve false intermediate beliefs, so this response does not fully succeed.

### Reliabilism
Alvin Goldman proposed that what matters is not justification in the traditional sense but **reliability**: a belief counts as knowledge if it is produced by a cognitive process that reliably produces true beliefs. Perception and memory are reliable processes; wishful thinking is not. Reliabilism explains why Gettier cases fail to yield knowledge—the process that produced the belief (mistaken evidence) is not reliably connected to the truth in the right way.

Critics worry that reliabilism has trouble accounting for the role of the subject’s own perspective. A belief might be produced by a reliable process without the subject having any access to that fact. Is that enough for knowledge?

### Contextualism
Some philosophers argue that the standards for knowledge vary with context. ‘Know’ is like ‘tall’ or ‘flat’—what counts as knowing depends on the situation, the stakes, and what alternatives are being considered. In everyday contexts, we apply relatively lenient standards; in philosophical discussions, the standards become more demanding.

Contextualism is controversial. Critics argue it cannot explain why philosophical reflection raises the standards rather than just changing the subject.

### Virtue Epistemology
Ernest Sosa and others have developed accounts that ground knowledge in **intellectual virtues**: stable, reliable cognitive capacities of the agent. Knowledge is not merely reliably produced true belief but belief that reflects the exercise of the agent’s own competence. On this view, the problem with Gettier cases is that the true belief is not a manifestation of the agent’s competence—luck plays too large a role.

## Why It Matters

The question of what knowledge is bears on practical questions. When do we have enough evidence to act? When should we defer to experts? What obligations does knowing something create? These questions cannot be answered without some account of what knowledge is.

They also bear on how we think about disagreement. If two people have the same evidence and reach different conclusions, at least one of them has made some error of reasoning or ignored something they should not have. Understanding knowledge helps us understand what has gone wrong.

## Summary

- The classical analysis defines knowledge as justified true belief
- Gettier cases show that JTB is not sufficient—justified true belief can arise by luck in a way that falls short of knowledge
- Responses include no-false-lemmas approaches, reliabilism, contextualism, and virtue epistemology
- The debate remains active; no consensus successor to JTB has emerged
