Epistemology is the branch of philosophy that studies knowledge, belief, truth, and justification. This cheat sheet helps students compare major theories about what knowledge is and how people can claim to know something. It is useful for reading philosophical arguments, writing essays, and evaluating everyday claims.
The goal is to make abstract ideas clear enough to use in discussion and analysis.
A common starting point is the idea that knowledge = justified true belief, but philosophers debate whether that formula is enough. Rationalism emphasizes reason, empiricism emphasizes experience, and skepticism challenges whether certainty is possible. Other theories focus on how beliefs are supported, such as foundationalism, coherentism, and reliabilism.
Strong epistemology asks not only what someone believes, but why the belief should count as knowledge.
Key Facts
- The traditional definition is knowledge = belief + truth + justification.
- A belief is a claim a person accepts as true, even if the claim later turns out to be false.
- Truth means a statement matches reality, so the claim 'water freezes at 0 degrees Celsius' is true under standard pressure.
- Justification means having good reasons or evidence for a belief, such as observation, logic, testimony, or reliable methods.
- Rationalism holds that reason and innate ideas are major sources of knowledge, often expressed as knowledge comes from reason.
- Empiricism holds that sense experience is the main source of knowledge, often expressed as knowledge comes from experience.
- Skepticism questions whether humans can know some things with certainty, especially claims about the external world, other minds, or the future.
- Reliabilism says a belief is justified when it is produced by a dependable process, such as accurate perception, valid reasoning, or careful scientific testing.
Vocabulary
- Epistemology
- Epistemology is the study of knowledge, including what it is, where it comes from, and how it can be justified.
- Justified True Belief
- Justified true belief is the theory that a person knows a claim when they believe it, it is true, and they have good reasons for it.
- Skepticism
- Skepticism is the view that some knowledge claims should be doubted or may be impossible to prove with certainty.
- Rationalism
- Rationalism is the theory that reason, logic, and innate ideas are central sources of knowledge.
- Empiricism
- Empiricism is the theory that knowledge comes primarily from sense experience and observation.
- Coherentism
- Coherentism is the theory that a belief is justified when it fits logically with a connected system of other beliefs.
Common Mistakes to Avoid
- Confusing belief with knowledge is a mistake because a belief can be false or unsupported, while knowledge requires truth and justification.
- Treating opinion as automatically equal to knowledge is wrong because opinions still need reasons, evidence, or reliable support to be justified.
- Assuming certainty is required for all knowledge can be misleading because many philosophers allow knowledge based on strong but not perfect evidence.
- Ignoring Gettier cases is a mistake because they show that justified true belief may still fail to count as knowledge when luck is involved.
- Mixing up rationalism and empiricism is wrong because rationalism emphasizes reason as a source of knowledge, while empiricism emphasizes sensory experience.
Practice Questions
- 1 A student believes the library closes at 6:00 because the official website says so, and the library does close at 6:00. Identify the belief, truth, and justification in this example.
- 2 Classify each source as rationalist or empiricist: solving 2 + 3 = 5 in your mind, seeing rain outside, proving a geometry theorem, tasting that soup is salty.
- 3 A clock stopped at 3:00 yesterday, but someone looks at it today exactly at 3:00 and believes the correct time is 3:00. Does this count as knowledge under justified true belief, and why might it be a Gettier-style problem?
- 4 Why might a skeptic argue that sense experience alone is not enough to guarantee knowledge of the external world?