Epistemology: The Nature of Knowledge, Theories of Truth, and the Modern Significance of Cartesian Skepticism
The traditional (Platonic) definition of knowledge: **Justified True Belief (JTB)** — a belief constitutes knowledge if it’s true, believed, and the believer has justification. This definition seemed complete until 1963, when Edmund Gettier published a 3-page paper with simple counterexamples showing JTB is insufficient — the **Gettier Problem**: a belief can be simultaneously true, believed, and justified while still not being knowledge (because the justification is only accidentally related to the belief’s truth). This paper overturned two millennia of epistemological consensus.
## Cartesian Methodological Doubt and Brain-in-a-Vat
Descartes’ *Meditations on First Philosophy* used **Methodological Doubt**: systematically doubting all possibly-doubtable beliefs, seeking absolutely certain foundations. His skeptical scenario: an evil demon might be controlling all my perceptions, making me believe there’s an external world that doesn’t actually exist. Even so, the fact of “I am doubting” establishes “I am thinking” (*Cogito*), establishing my existence — Descartes’ Archimedean point for rebuilding knowledge.
The modern version: **Brain in a Vat** — if your brain were removed and placed in a nutrient vat with a supercomputer simulating all sensory input, how would you know this isn’t your current situation? *The Matrix* is the popular rendition of this philosophical scenario. Hilary Putnam’s *Reason, Truth and History* offers a counter (semantic externalism argument), but debate continues.
## Theories of Truth
**Correspondence Theory**: truth consists in propositions corresponding to reality — “Snow is white” is true if and only if snow actually is white; **Coherence Theory**: true propositions are those coherent with other beliefs; **Pragmatist Theory** (William James): truth is belief that works in practice; **Deflationism**: no further theory of truth is needed — “‘Snow is white’ is true” is equivalent to “Snow is white.”
