Epistemology: What Can We Know?

Core Philosophical Problems

Course 3 · Chapter 3 · Epistemology: What Can We Know?

Course 2 already spent four chapters (2 through 4, plus Moore in Chapter 7) working through epistemology's own major historical positions. This chapter organizes that same material by question rather than by century — and adds the one genuinely new centerpiece those chapters never covered: what "knowledge" itself actually means.

The Traditional Definition

For roughly two thousand years, philosophy's working definition of knowledge was justified true belief (JTB): you know something if and only if (1) you believe it, (2) it's actually true, and (3) you have genuine justification for believing it.

A Genuine Correction — this definition is traditionally credited to Plato. The real irony: in his own dialogue Theaetetus, Plato actually argues against this very account of knowledge, not for it. The formula that carries his name is closer to something later philosophy extracted and formalized from the discussion he staged than a position he himself endorsed.

Gettier's Real Counterexample

The JTB definition stood essentially unchallenged until Edmund Gettier's real, remarkably short 1963 paper, "Is Justified True Belief Knowledge?" — just three pages long, and enough to permanently reopen a question philosophy had treated as settled for two millennia.

The Smith and Jones Case

Smith has strong evidence that Jones will get a job, and that Jones has ten coins in his pocket. Smith reasonably infers: "The man who will get the job has ten coins in his pocket." As it turns out, Smith himself gets the job — and, by sheer coincidence, Smith also happens to have ten coins in his own pocket, though he has no idea how many coins he's carrying. Smith's belief was justified, and it's true — but it isn't knowledge, because it's true for a reason entirely disconnected from the actual justification Smith had for believing it.

Gettier's real point: justified true belief can happen almost by accident, which means the traditional three conditions aren't actually sufficient for genuine knowledge — a fourth condition is needed, and philosophers still haven't fully agreed on what it should be.

Foundationalism vs. Coherentism

A separate question: what justifies a belief in the first place? Every justification seems to need its own further justification — and if that chain runs on forever, nothing ever actually gets justified. This is the real regress problem, and two theories offer competing solutions.

Foundationalism

Some beliefs are "basic" — justified in themselves, needing no further support — and everything else is justified by ultimately resting on them.

Coherentism

No belief needs a privileged foundation; justification comes from how well a belief fits into a whole, mutually-supporting web of other beliefs.

A Direct Echo of Course 2 Descartes's whole project in Course 2, Chapter 2 is a textbook real example of foundationalism in action — the cogito was built to be exactly the kind of basic, self-justifying belief foundationalism needs, with everything else meant to be rebuilt on top of it. Hume's own bundle theory, by contrast, fits more naturally with a coherentist picture — no single fixed anchor point, just perceptions connected to each other by habit and resemblance.

Rationalism, Empiricism & Skepticism, Revisited

Course 2 already covered the major historical answers to "how do we know anything at all?" in full depth. Placed side by side here, as one thematic table rather than three separate chapters:

	Rationalism (C2, Ch.2)	Empiricism (C2, Ch.3)	Kant (C2, Ch.4)
Primary source	Reason and deduction	Sense experience	The mind's own structuring categories
Certainty available?	Yes — for reason's own deductions	Only for immediate perception	Yes — for synthetic a priori truths
What ultimately survives	The cogito	A bundle of perceptions (Hume)	Phenomena, never noumena

Skepticism itself has a real, genuine split in how philosophy has tried to answer it. Descartes's own method (Course 2, Ch.2) tries to answer the skeptic on the skeptic's own terms — doubt everything, then rebuild from one indubitable foundation. G.E. Moore's real 1939 approach (Course 2, Ch.7) refuses to play that game at all — "Here is one hand" treats everyday certainty as more secure than any abstract skeptical premise, putting the burden back on the skeptic's own argument rather than on common sense.

Where This Goes Next — Chapter 4 turns from what we can know to what actually exists: free will, personal identity, and the mind itself, pulling together Aristotle, Descartes, Hume, and Chalmers's own hard problem from Course 2's closing chapters.

Questions to Sit With

Reflection 1

Smith's belief in the Gettier case is justified and true, yet doesn't feel like real knowledge. Can you put into words exactly what's missing, without just repeating "luck"?

Reflection 2

Foundationalism needs some belief that's justified without needing any further justification. Can you think of a genuine candidate for a truly "basic" belief — one that seems to need no further support at all?

Reflection 3

Descartes tries to answer skepticism on its own terms; Moore refuses to engage with it at all. Which strategy do you find more satisfying as an actual response to doubt?

Quick Reference — Chapter 3

JTB — belief + truth + justification; credited to Plato, who actually argued against it in the Theaetetus
Gettier's counterexample — real 1963 three-page paper; the Smith/Jones case shows JTB isn't sufficient for knowledge
Foundationalism (basic, self-justifying beliefs) vs. coherentism (justification via a coherent web) — two answers to the regress problem
Course 2's rationalism, empiricism, and Kant recapped as three real historical answers to the same question
Two real strategies against skepticism — Descartes answering it on its own terms vs. Moore refusing to engage it at all