---
date: '2025-12-18'
description: cartesian skepticism employing the closure principles
id: Skepticism
modified: 2026-06-05 15:08:24 GMT-04:00
tags:
  - philosophy
  - pattern
title: Skepticism
created: '2025-12-18'
published: '2025-12-18'
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---
Philosophical skepticism targets knowledge claims that ordinary life takes for granted. The skeptical move is stronger than “I am unsure how many stars are in the Milky Way.” It asks whether I know claims that I normally treat as settled, e.g. “I have hands.”

The Cartesian argument uses closure. If $S$ knows $p$, knows that $p \to q$, and competently infers $q$, then $S$ knows $q$. If I know that I have hands, and I know that having hands rules out being a brain in a vat, closure seems to give me knowledge that I am not a brain in a vat. The skeptic flips it around: I do not know that I am not a brain in a vat, so I do not know that I have hands.

Knowledge also needs the right [[thoughts/doxastic attitude]]. The coarse attitudes are belief, disbelief, and suspension of judgment. I can fail to know $p$ because I do not believe $p$, or because I believe $p$ without justification.

Nozick’s sensitivity condition says that $S$ knows $p$ only if $S$ would not believe $p$ in the nearest worlds where $p$ is false. This lets ordinary hand knowledge pass while denying knowledge of the anti-skeptical claim. If I were a brain in a vat, I would still believe I was not one.

re [skepticism](https://plato.stanford.edu/entries/skepticism/) and [epistemic closure](https://plato.stanford.edu/entries/closure-epistemic/)