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How does a guess become knowledge—and how much doubt remains when the evidence seems clear?
In The Principles of Science, William Stanley Jevons follows reasoning from its simplest rules to the testing of a theory. He begins with a bold claim: all inference rests on putting like for like. From there, he explores how logic, induction and probability help us move from particular facts toward general laws, without mistaking a likely answer for certainty.
The book then turns to the work of discovery: measuring, observing, arranging experiments and forming hypotheses. Jevons shows why every measurement carries error and why a useful guess needs a test. Analogy and classification guide the search, but the laws we find remain limited by the facts we have. The result is a study of both science’s reach and its limits.
What you’ll discover
- The rules beneath reasoning Explore Jevons’s claim that putting like for like lies at the heart of inference.
- Evidence without certainty See how probability weighs evidence when observations support a conclusion but cannot make it certain.
- Numbers with room for doubt Discover why measurement advances science even though no measurement is perfectly exact.
- The value of a guess Follow the role of hypotheses, analogy and classification in the search for new knowledge.
- Questions that shape experiments Distinguish watching what nature offers from arranging conditions to see what follows.
Who will love it
You will enjoy this if you like to see how knowing works, from logic puzzles and probability to experiments and great discoveries. It rewards anyone curious about how scientists think and how evidence is weighed.
What’s inside
The key ideas, in the 15-minute summary
- Science depends on nature repeating herself
- Reasoning substitutes one equal for another
- Strike out what the facts forbid
- Induction runs deduction in reverse
- Counting keeps difference and discards kind
- Probability expresses degrees of knowledge
- Experiments separate causes from irrelevant circumstances
- Hypotheses earn support through tested predictions
- Scientific judgment joins logic with evidence
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The Principles of Science
by William Stanley Jevons · 1874
A Victorian logician builds a reasoning machine and argues that induction is just deduction run backwards.
Challenging10–20 hours to read20 languages
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In short
Picture a world where nothing repeats. William Stanley Jevons opens The Principles of Science by describing that world, and then shows why ours is not one.
The Principles of Science at a glance
- Reading time
- About 18 h 10 min14 h 25 min fast, 21 h 35 min slow
- Length
- 259,300 words
- Library level
- Challenging long sentences, a rich vocabulary
- First published
- 1874by William Stanley Jevons
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
Science begins with finding sameness in difference
Jevons opens with a simple claim. Every act of scientific reasoning rests on identity, which he also calls likeness or resemblance. We can pass from one case to another only because the two cases share something.
He makes the point by imagining a chaotic universe. Suppose events came out of an infinite lottery, so that no two things went together more often than any other two. Then knowledge would be a mere memory of past coincidences, and the mind could say nothing about what comes next. Our world is not like that, because substances keep fixed characters and iron does not change into gold.
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- 15-minute summary
- The key ideas of the whole book in about 13 minutes. A good first look, or a refresher.
Details
- First published
- 1874
- Language
- English
- Level
- Challenging
Cite this edition
Jevons, William Stanley. The Principles of Science. Library of Alexandria, 2026, libraryofalexandria.com/products/the-principles-of-science.
Jevons, W. S. (2026). The principles of science. Library of Alexandria. https://libraryofalexandria.com/products/the-principles-of-science (Original work published 1874)
Jevons, William Stanley. The Principles of Science. Library of Alexandria, 2026. https://libraryofalexandria.com/products/the-principles-of-science.
@book{jevons2026principles,
author = {Jevons, William Stanley},
title = {The Principles of Science},
publisher = {Library of Alexandria},
year = {2026},
url = {https://libraryofalexandria.com/products/the-principles-of-science},
note = {First published 1874}
}
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What is The Principles of Science about?
It is a treatise on logic and scientific method. Jevons explains how reasoning works, how probability measures evidence, how measurement and experiment are done well, and how hypotheses, analogy and classification lead to discovery, all with examples from many sciences.
What is the Logical Machine in Jevons's book?
It is a reasoning device he built to carry out logical inference mechanically. It works on the logical alphabet, a list of all combinations of terms, and strikes out those that the premises forbid, leaving the valid conclusions.
What does Jevons mean by saying induction is inverse deduction?
He means that finding a law from facts is the reverse of deducing facts from a law. You guess a law, work out its consequences, and keep it if they agree with observation. There is no separate inductive method.
The author
William Stanley Jevons
1835–1882 · English economist and logician
English economist and logician.
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