Five-minute digest
Illustrations of the Logic of Science
Summary
Illustrations of the Logic of Science is a series of six essays that Charles Sanders Peirce published in Popular Science Monthly between November 1877 and August 1878. Written for a general educated readership, they set out a theory of inquiry, a rule for clarifying the meaning of ideas, a frequency account of probability, and a three-part classification of inference. The library text is Part I of Chance, Love, and Logic, the 1923 collection edited by Morris R. Cohen. The Fixation of Belief begins by observing that everyone thinks himself a good reasoner. Peirce treats belief as a settled habit that guides action and doubt as a restless state that drives us to inquire until belief returns. He then compares four ways of settling opinion: tenacity, which clings to a belief and avoids contrary evidence; authority, by which a state or institution imposes belief; the a priori method, which accepts what seems agreeable to reason; and the method of science, which lets belief be determined by real things independent of what anyone thinks. Only the last, he argues, can correct itself. How to Make Our Ideas Clear criticizes Descartes's and Leibniz's tests of clear and distinct ideas and proposes a third grade of clearness: consider the practical effects we conceive an object to have, for our conception of those effects is the whole of our conception of it. Peirce applies the rule to hardness, weight, force and reality, and defines truth as the opinion investigators are destined to reach if inquiry continues long enough. The Doctrine of Chances defines probability as the ratio of true conclusions among arguments of a kind in the long run. Because a single person's life is finite, Peirce argues that sound reasoning requires identifying one's interests with an unlimited community of inquirers, and he likens the needed sentiments to St. Paul's faith, hope and charity. The Probability of Induction rejects the conceptualist view, expounded by Augustus De Morgan, that assigns probabilities to hypotheses without evidence, and rests induction on its self-correcting character. The Order of Nature asks whether the regularity of the world proves design and argues that even a chance world would show some order; it closes with reflections on science and religion. Deduction, Induction, and Hypothesis uses a bag of white beans to set out three forms of inference and connects them with attention, habit and feeling. William James's 1898 lecture crediting Peirce with the principle of pragmatism made the second essay famous.
Top Lessons
How beliefs get settled
Peirce observes that people settle their opinions in several ways: by holding on stubbornly, by deferring to authority, by accepting what seems reasonable, or by investigating. He grants the strengths of each but argues that only investigation lets the world itself correct us.
Meaning shows itself in consequences
Peirce's rule for clear ideas asks what difference a concept would make in conceivable experience. If two ideas make no conceivable difference, they are the same idea in different words. The rule exposes empty disputes and sharpens real ones.
Good reasoning is a shared enterprise
Because probability concerns the long run, and no single life is long enough, Peirce concludes that a reasoner must care about the whole community of inquirers, present and future. He finds in this a moral as well as a logical demand.
Three ways to reason
Deduction draws out what is contained in a rule; induction generalizes from samples; hypothesis guesses the case that would explain a surprising fact. Peirce's bean-bag example shows how these forms fit together in scientific work.
Verified Quotes
“Few persons care to study logic, because everybody conceives himself to be proficient enough in the art of reasoning already.”
“The irritation of doubt causes a struggle to attain a state of belief.”
“To satisfy our doubts, therefore, it is necessary that a method should be found by which our beliefs may be caused by nothing human, but by some external permanency—by something upon which our thinking has no effect.”
“The genius of a man’s logical method should be loved and reverenced as his bride, whom he has chosen from all the world.”
“Consider what effects, which might conceivably have practical bearings, we conceive the object of our conception to have. Then, our conception of these effects is the whole of our conception of the object.”
“He who would not sacrifice his own soul to save the whole world, is, as it seems to me, illogical in all his inferences, collectively. Logic is rooted in the social principle.”
“Hypothesis is where we find some very curious circumstance, which would be explained by the supposition that it was a case of a certain general rule, and thereupon adopt that supposition.”
Medical Lens
The essays are logic, not medicine, but Peirce's psychology of belief borrows from the physiology of his day. He compares doubt to the irritation of a nerve and belief to a nervous association, such as the smell of a peach making the mouth water, and treats belief as a habit of action. In the last essay he maps hypothesis, induction and deduction onto feeling, habit and attention, the last compared to nervous discharge. His frequency theory of probability and his insistence on random sampling are part of the background of later statistical method in medicine; with Joseph Jastrow he later ran a psychophysical experiment (published 1885) that historians of statistics often cite as an early use of randomization and blinding. These connections are conceptual and should not be overstated.
- The Fixation of Belief, III
Doubt is likened to the irritation of a nerve and reflex action, and belief to a nervous habit.
- How to Make Our Ideas Clear, I
An unclear idea in a young man's head is compared to an obstruction in an artery starving the brain.
- Deduction, Induction, and Hypothesis, V
Hypothesis is linked to emotion, induction to habit and deduction to attention and nervous discharge.