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What if chance is simply a name for what we do not know?
In A Philosophical Essay on Probabilities, Pierre-Simon Laplace takes uncertainty out of the gambling room and into daily judgment. Writing for readers who are not mathematicians, he uses almost no formulas. Dice, coins, coloured balls, birth records and court verdicts show how probability helps us reason when the facts are incomplete.
Laplace imagines a mind that knows every force and position in nature and can see the whole future. We have no such knowledge. Instead, he explores how to combine chances, trace effects back to likely causes, and weigh evidence. The stakes reach from trust in a witness to the strength of a scientific hypothesis.
What you’ll discover
- A clear starting point Explore what probability means through equally possible cases, coins, dice and coloured balls.
- Clues that lead backward Follow the reasoning that moves from an observed effect toward its likely cause.
- Evidence in human affairs Consider how probability can help weigh testimony, jury decisions and votes.
- Patterns beneath uncertain events See how averages settle toward steady values even when single outcomes remain uncertain.
- Common sense under scrutiny Examine why a long run of one outcome need not make its opposite likelier.
Who will love it
Readers who enjoy clear thinking about luck, evidence and risk will appreciate this essay. It also suits those curious about how scientists and judges weigh uncertain facts.
What’s inside
The key ideas, in the 15-minute summary
- Uncertainty begins with what we lack
- Probability depends on what you know
- Every uncertain link reduces confidence
- Evidence helps us reason toward causes
- A prize means different things
- Many events reveal a steadier pattern
- Test the claim and the teller
- Public decisions need informed judgment
- Let evidence guide your confidence
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A Philosophical Essay on Probabilities
by Pierre-Simon Laplace · 1814
A French mathematician imagines a mind that knows every force in nature and sees the future as clearly as the past.
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“the theory of probabilities is, at bottom, only common sense reduced to calculation”
In short
Imagine a mind that knows every force in nature and every position of every atom at a single instant. For that mind, Laplace says, nothing is uncertain, and the future lies open like the past.
A Philosophical Essay on Probabilities at a glance
- Reading time
- About 3 h 15 min2 h 35 min fast, 3 h 50 min slow
- Length
- 46,300 words
- Library level
- Challenging long sentences, a rich vocabulary
- First published
- 1814by Pierre-Simon Laplace
Reading time at 238 words a minute (fast 300, slow 200). How long the classics take to read · Updated
From the 15-minute summary · Key idea 1
Chance is only a measure of our ignorance
Laplace begins with a firm claim. Every event follows from the laws of nature as surely as the sun follows its course. People speak of chance only when they cannot see the causes. As knowledge grows, those imaginary causes fade away.
Then comes his best-known picture. Imagine an intelligence that knows all the forces of nature and the positions of all things at one instant, and that can analyze them. It would express in one formula the motion of the largest bodies and the lightest atom. For it, the future would be as present as the past.
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Details
- First published
- 1814
- Language
- English
- Reading time
- 3 h 50 min
- Level
- Challenging
Cite this edition
Laplace, Pierre-Simon. A Philosophical Essay on Probabilities. Library of Alexandria, 2026, libraryofalexandria.com/products/a-philosophical-essay-on-probabilities.
Laplace, P.-S. (2026). A philosophical essay on probabilities. Library of Alexandria. https://libraryofalexandria.com/products/a-philosophical-essay-on-probabilities (Original work published 1814)
Laplace, Pierre-Simon. A Philosophical Essay on Probabilities. Library of Alexandria, 2026. https://libraryofalexandria.com/products/a-philosophical-essay-on-probabilities.
@book{laplace2026philosophical,
author = {Laplace, Pierre-Simon},
title = {A Philosophical Essay on Probabilities},
publisher = {Library of Alexandria},
year = {2026},
url = {https://libraryofalexandria.com/products/a-philosophical-essay-on-probabilities},
note = {First published 1814}
}
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What is A Philosophical Essay on Probabilities about?
It explains how to measure chance and uncertainty. Laplace sets out the principles of probability in plain language, then applies them to games, astronomy, witnesses, juries, mortality tables and insurance, and warns against common errors in judging odds.
What is Laplace's demon in this book?
It is his picture of a vast intelligence that knows every force and position in nature at one instant. For it the future is as clear as the past. Humans, he says, approach it only faintly, through science.
Is the essay written for general readers or only mathematicians?
Laplace wrote it without algebra for a general audience. It grew from a 1795 lecture to the normal schools, and most chapters explain ideas through urns, coins, dice and real examples from astronomy, births and courts.
The author
Pierre-Simon Laplace
1749–1827 · French mathematician and astronomer
Pierre-Simon Laplace was a French mathematician and astronomer. He was born in Beaumont-en-Auge, Normandy, in 1749 and died in Paris in 1827. He worked in Paris and wrote on mathematics, astronomy, and probability. His works include Celestial Mechanics, published from 1799 to 1825, and A Philosophical Essay on Probabilities, published in 1814.
“the theory of probabilities is, at bottom, only common sense reduced to calculation”
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