---
title: "Descartes’ demon · Simulation Hypothesis"
url: https://simulation-hypothesis.com/thinkers/descartes
description: "Suppose a being of great power has put all its effort into deceiving you. What’s left? René Descartes, Meditations on First Philosophy · 1641"
license: https://creativecommons.org/licenses/by/4.0/
credit: "Ross Allan Dahl, Simulation Hypothesis (simulation-hypothesis.com)"
---

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# Descartes’ demon

René Descartes, Meditations on First Philosophy · 1641

Suppose a being of great power has put all its effort into deceiving you. What’s left?

Descartes wanted something he couldn’t doubt, so he started by doubting everything on purpose. First the senses, which have fooled him before and might be fooling him now. Then the whole of waking life, since nothing marks it off for sure from a dream. Finally he imagines a deceiver. It isn’t God, who wouldn’t lie. It’s a malicious demon of enormous power and cunning. The demon has made the sky, the air, the earth, colours, shapes, sounds and every outside thing into illusions, set up to trap his judgement.

The demon is a thought experiment about the limits of evidence. It’s also the first simulation hypothesis in the modern sense: a complete, coherent, deliberately made world that’s false all the way through. The key word is complete. The demon makes no mistakes, so there’s no glitch to find. Whatever test you run, the result has already been rendered.

One thing survives. If he’s being deceived, he exists, because there has to be something for the demon to deceive. The act of doubting can’t itself be doubted away. This is the cogito, and it’s a much smaller foothold than people remember. It gives you a thinking thing, right now, and nothing more. Everything else Descartes builds on it, including the outside world, he rebuilds by arguing that a good God wouldn’t allow such a demon. Most readers find the demolition more convincing than the rebuilding.

Swap the demon for a data centre and the argument doesn’t change. Every era states the worry with the most vivid image of deception it has, and in 1641 that image was a demon.

The demon also gives the site its idea of an operator: someone or something is running the scenario. The operator on a break in the Slot dial is a watered-down version of Descartes’ deceiver. It’s still all-powerful inside the world and still not answering questions, but it’s barely paying attention.

In the sandbox · Slot · The operator on a breakThe demon is the operator. Every scenario has one. The Honesty axis of the ethics meters asks the demon’s question from the inhabitants’ side: could they find out, even in principle?

[Open the sandbox ▸](https://simulation-hypothesis.com/sandbox)

In the trees

[Suppose you are the only one · Ethics](https://simulation-hypothesis.com/trees/ethics?n=x-alone)

## Sources

Meditations on First Philosophy, First and Second Meditations

Descartes, 1641\. The demon appears at the end of the First Meditation.

[Descartes’ Epistemology](https://plato.stanford.edu/entries/descartes-epistemology/)

Stanford Encyclopedia of Philosophy

In the Library

[Descartes’ demon](https://simulation-hypothesis.com/library/evil-demon)[Skepticism](https://simulation-hypothesis.com/library/skepticism)[Epistemology](https://simulation-hypothesis.com/library/epistemology)

[◂ Calderón’s life is a dream](https://simulation-hypothesis.com/thinkers/calderon)[Berkeley’s perceiver ▸](https://simulation-hypothesis.com/thinkers/berkeley)