# Critical rationalism

> Knowledge grows through conjecture and criticism, with claims kept open to refutation rather than justified as certain.

- HTML version: https://robbiepalmer.me/ideas/critical-rationalism
- Source: https://plato.stanford.edu/entries/popper/

Critical rationalism is Karl Popper's account of knowledge as conjectural and
open to criticism. We propose explanations, draw out their consequences, and
try to find errors. Argument and critical discussion let us prefer one claim
without proving it. Experience matters because it can expose a mistake, not
because confirming instances make a universal claim certain.

## Conjectures and refutations

Popper rejected induction as proof of a universal theory. Cases that fit a
claim do not entail that the next case will fit. A conflicting observation,
however, can count against a universal prediction through deduction.

This makes [falsifiability](/ideas/falsifiability) a criterion for scientific
claims. A theory is falsifiable when some possible observation conflicts with
it. A claim compatible with every possible outcome takes no empirical risk.
Surviving a severe test corroborates a theory, but it does not verify the theory
or assign it a probability of truth.

The method starts with a problem rather than neutral data. Researchers propose
a solution, specify risky consequences, and compare it with alternatives. A
theory earns interest when it solves the problem or survives a test that
defeats its rivals.

Critical rationalism applies beyond laboratory science. Popper defended
piecemeal institutional change because limited interventions make errors easier
to identify and reverse. He opposed plans that claimed knowledge of inevitable
historical outcomes and political systems that suppressed criticism. The same
fallibilism connects his philosophy of science with his defence of an open
society.

## Why falsification is not mechanical

A failed prediction never tests one statement alone. It also depends on
instruments, initial conditions, auxiliary hypotheses, and the interpretation
of the result. A conflict shows that something in this set is wrong. Logic does
not say which part to abandon.

Popper knew that an isolated observation should not automatically defeat a
theory. A scientific community must decide whether it accepts the observation
statement and whether the conflict is reproducible. This saves the method from
a crude one-strike rule, but it gives judgement and convention a larger role
than the simple logic of refutation suggests.

[Theory-ladenness](/ideas/theory-ladenness) sharpens the problem. Potential
refutations are described through concepts and theories that may themselves be
at issue. Tests can still find errors, but no observation supplies an
incorrigible verdict from outside every framework.

## Criticisms and limits

Thomas Kuhn argued that scientific history does not resemble a sequence of
theories discarded whenever anomalies appear. Normal science often retains a
framework while researchers investigate troublesome results. Imre Lakatos later
described research programmes whose central commitments sit inside a changing
set of auxiliary hypotheses. Both accounts ask whether Popper's rules describe
actual scientific change or prescribe an ideal for criticism.

Theories can also differ in explanatory reach without producing an immediate
decisive test. Judgements about simplicity, fruitfulness, and problem choice
then matter. Critical rationalism can treat those judgements as open to
criticism, but it cannot turn all of them into falsification tests.

Critical rationalism's durable claim is that knowledge can improve without an
unquestionable foundation. Claims should expose where they might be wrong, and
revisions should solve more than the failure that prompted them.
[Postpositivism](/ideas/postpositivism) shares that fallibilism while giving
more attention to history, communities, values, and the production of
evidence.

## Sources

* Thornton, Stephen. ["Karl
  Popper"](https://plato.stanford.edu/archives/spr2025/entries/popper/). *The
  Stanford Encyclopedia of Philosophy*, 2025.
* Popper, Karl. *The Logic of Scientific Discovery*. Hutchinson, 1959.
* Popper, Karl. *Conjectures and Refutations*. Routledge, 1963.
* Lakatos, Imre. *The Methodology of Scientific Research Programmes*.
  Cambridge University Press, 1978.

## Related ideas

- [Epistemology](https://robbiepalmer.me/ideas/epistemology.md): How we know what we claim to know, what justifies a belief, and when new evidence should change it.
- [Falsifiability](https://robbiepalmer.me/ideas/falsifiability.md): A claim is falsifiable when some possible observation could count against it, though real tests examine a bundle of assumptions.
- [Logical empiricism](https://robbiepalmer.me/ideas/logical-empiricism.md): A movement that used logic and analysis to connect scientific claims with public evidence and to clarify the role of philosophy.
- [Postpositivism](https://robbiepalmer.me/ideas/postpositivism.md): Empirical inquiry can pursue objectivity while accepting fallible evidence, theory-laden observation, and the influence of values.
- [Theory-ladenness](https://robbiepalmer.me/ideas/theory-ladenness.md): Observations depend on prior ideas about what to notice, how to measure it, and what the result means.

## Where it appears

- Blog post: [The Philosophy of Data Science](https://robbiepalmer.me/blog/2022-03-02-the-philosophy-of-data-science.md)

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