Problem of demarcation = the problem of finding a criterion that distinguishes between empirical sciences from non-science (mathematics, logic, metaphysics, etc.) i.e. distinguishing science from pseudo-science,
For popper-1934-logic-of-scientific-discovery, this was a central issue in the philosophy of science and called it “Kant’s problem” as Kant saw it as a fundamental problem of the theory of knowledge.
Logical empiricism’s criterion
logical-empiricism implied a criterion based on their verification theory of meaning = the meaning of a claim lies in its method of verification. This would make verifiable claims scientific and unverifiable ones metaphysical or meaningless
Popper rejected the verifiability criterion for several reasons:
- It counts existential statements as empirical even though they cannot be falsified (proving something doesn’t exist in one place doesn’t mean it can’t exist elsewhere)
- It treats universal statements as meaningless because they cannot be conclusively verified, even though they can clearly be shown to be false
- The verification criterion is itself meaningless since it cannot be verified
Importantly, Popper believed that we can never be fully certain about factual issues (known as fallibilism). Most philosophers of science accept fallibilism and logical-empiricism believes that it is reasonable in increasing our confidence in the truth of a theory when it passes observational evidence, Popper disagrees. The Principle of induction offered by Reichenbach incorporates fallibilism but still fails for Popper due to problem of induction.
methodological vs metaphysical distinction
important insight: logical-empiricism believed they needed to discover a difference in the nature of things between science and metaphysics - that metaphysics is inherently nonsense.
Popper saw the criterion of demarcation as a proposal for convention - a methodological choice about how we define science, not a metaphysical truth about what kinds of statements are meaningful.
Popper’s alternative - Falsifiability as a criterion of demarcation
Popper’s proposal for the criterion of demarcation is falsifiability = it must be possible for an empirical scientific system to be refuted by experience.
Instead of trying to verify or confirm theories through accumulating positive evidence, Popper argued that science advances through falsification - by attempting to prove theories wrong.
Example =
- Not empirical (unfalsifiable): “It will rain or not rain tomorrow” - cannot be refuted; it’s true no matter what happens
- Empirical (falsifiable): “It will rain tomorrow” - can be refuted by observation
Popper argued that scientific theories can only be falsified, not inductively confirmed. No amount of positive evidence can verify a theory but a single contradictory observation can refute it.
Falsification relies purely on deductive logic:
- If the hypothesis is true, then the prediction is true.
- The prediction is false.
- Therefore, the hypothesis is false.
Unlike hypothetico-deductivism, which uses both deductive and inductive arguments, Popper’s approach rejects the inductive step where predictions confirm hypotheses. He accepts only the deductive argument that uses failed predictions to falsify hypotheses.
The ad hoc objection
One objection Popper addresses: it’s always possible to evade falsification through ad hoc hypotheses or changing definition ad hoc.
Ad hoc moves are designed to save a theory from being proven wrong when faced with contradicting evidence. An ad hoc hypothesis is a modification to a theory designed to save it from being proven wrong when faced with contradicting evidence.
Popper’s response: the empirical method itself is characterized by its manner of exposing theories to falsification. The difference between science and pseudo-science isn’t that science gets falsified and pseudo-science doesn’t, but that science actively seeks falsification while pseudo-science actively evades it.
Example of an ad hoc hypothesis
Galileo concluded that there are craters and mountains on the moon’s surface based on observations made with his telescope. This prediction conflicted with the predominant
Aristotelian that the moon is perfectly smooth.
Instead of conceding that their theory had been falsified, Aristotelians argued that there was an invisible substance on the moon that filled craters and valleys between the
mountains. They claimed that there was no way of detecting this substance.
falsifiability as a solution to the problem of induction
Choosing falsifiability as the criterion of demarcation solves the problem of induction.
The apparent contradiction was:
- Logical-empiricism claimed: the only genuine source of knowledge is experience, and all empirical statements must be conclusively verified
- Hume showed: inductive inferences cannot be rationally justified
By renouncing the verification principle and instead admitting statements as empirical only if they can be falsified through systematic attempts, the contradiction disappears. The method of falsification presupposes no inductive inference - only deductive logic