Lesson · 4 min Stretch
Laplace’s Demon
In one line If the past and the laws fix everything, are your choices up to you? And if nothing fixes them, are they just chance?
In 1814 the mathematician Pierre-Simon Laplace imagined an intellect that knew the position of every particle and every law of nature. For such a mind, he wrote, nothing would be uncertain: the future would be as plain as the past. This is the picture behind determinism.
Peter van Inwagen turned it into the consequence argument. The distant past is not up to us, and neither are the laws of nature. If determinism is true, our acts follow from those two. So our acts are not up to us either.
But dropping determinism does not obviously help. If a choice is not fixed by anything, including your reasons, it looks like chance, and chance is not control. This is the luck objection. Free will seems squeezed from both sides.
Go deeper
Modern physics complicates the picture: quantum mechanics, on its standard readings, makes some events probabilistic rather than fixed. Many philosophers think this does not rescue free will, since random events in the brain would not make choices more yours. Libertarians such as Robert Kane reply that indeterminism during hard choices, between competing reasons, could leave the choice still the agent’s own.
The perfect forecast
A researcher claims an app can predict, with near-perfect accuracy, what dessert each user will order. Mira tests it, and the app is right every time.
She feels uneasy: if her choice could be known in advance, was it really hers? Her friend points out the other side. If her order were random, the app would fail, but Mira would not feel more in charge of her dessert.
Try this today Recall a choice you made today. Ask whether a perfect predictor could have foreseen it, and whether that would bother you.
Cite or share this lesson
A plain reference you can paste into notes or an essay:
Quest2Reason. “Laplace’s Demon.” https://quest2reason.com/learn/lesson/laplaces-demon. Accessed 13 November 2026.
Sources
- Stanford Encyclopedia of Philosophy, “Causal Determinism” — Explains determinism, Laplace’s intellect and the bearing of physics.
- Wikipedia, “Consequence argument” — Sets out van Inwagen’s argument step by step.
- Stanford Encyclopedia of Philosophy, “Incompatibilist (Nondeterministic) Theories of Free Will” — Covers libertarian views, Kane and the luck objection.