Karl Popper & The Philosophy of Science What Makes a Theory Scientific?

Philosophy of Science The Philosophy of Science deals with many issues, including:

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The relationship of scientific statements to other kinds of statements.

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The status of scientific claims.

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Should the entities described by science (e.g. subatomic particles) be understood as real, or merely explanatory posits?

Whether science can provide knowledge.

Karl Popper • • •

1902-1994

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Famous for his Philosophy of Science and his criticisms of totalitarian government.

Austrian/Jewish Fled Austria for New Zealand in 1937 to escape the Nazis.

Popper’s Question Which theories are Scientific?

• Take two theories about medicine: 1. Modern Medical Science. 2. Lee’s theory of Magical Medicine.

What makes (1) scientific and (2) not?

Answer 1. Confirmation • The modern theory of medicine is

confirmed by the evidence, but Lee’s theory of Magical Medicine is not.

• But I can make my theory of Magical

Medicine completely consistent with the evidence (like a conspiracy theory).

• e.g. I ascribe different maladies to the influences of different evil spirits.

• So confirmation does not seem to do it.

Answer 2. Explanatory Power • Modern medicine is better than Magic

because it enables us to explain what is happening in cases of illness.

• But so does Magic: people are possessed by evil spirits.

• Why is the explanation offered by modern medicine a better one than that offered by Magic?

Answer 3. Useful • Modern Medical Science is better than

Magical Medicine because it enables us to predict the future in useful ways.

• But a theory need not be true or even scientific to do this.

• e.g. I believe that spirits cause the seasons.

• It depends on what people consider useful.

Answer 4. Falsifiability • Popper: in order to be considered a

candidate scientific theory, a theory must be capable of being falsified.

• That is, there must be possible events that would cause us to abandon it.

• This is not the case with Magic or

conspiracy theories because no matter what the evidence, they can be made consistent with it.

Observational Consequences • Statements of a scientific theory have observational consequences.

• We can express these in conditionals. • e.g. “If theory X is true, then Y must occur.”

• This means that if Y doesn’t occur then theory X must be false.

No Confirmation • Popper: a scientific theory can never be

proven to be true (confirmed), it can only ever be proven false.

• Our current scientific theory is a good one because it has not yet been proven false, despite being subjected to a barrage of observational tests.

• The more tests, the “fitter” the theory.

• If scientific theories must be falsifiable, then it turns out that Magic cannot be a science, because it can’t ever be proven false. This is also what distinguishes conspiracy theories from other theories.

• Similarly with beliefs in beings that no-one

could ever detect by any means. There might indeed be such beings, but the theory that claims their existence is not a scientific theory because it is not testable.

Induction Again • The Problem of Induction claimed that we

had no reason to believe in the uniformity of nature over time and space. Hence we have no reason to regard science as more than speculation.

• Popper: To imagine that Science could ever

prove the uniformity of nature is to misunderstand science. Science can’t prove anything. It merely consists of falsifiable theories that have not yet been falsified.

• Popper: Hume is right that we cannot

“prove” any theory to be absolutely correct.

• Popper: But it is the case that we can

absolutely prove that a theory is incorrect (by showing it is falsified).

• Popper: Science does not in fact make use of induction.

• It is conjectural. We just hang on to the

theories that survive all the various slings and arrows we throw at them.

• Has Popper “solved” the problem? • Which “sciences” pass his test of falsifiability?

• Popper thought that Freud’s Psychoanalysis did not.

• What does it mean for the evolution vs Intelligent Design debate?

Against Falsificationism • Kitcher: take Newton’s laws + the theory of gravitation.

• This theory predicts that an apple released from a tree will fall and hit the ground.

• If that doesn’t happen, we must reject the theory (this is required by Popper).

• But it isn’t clear that we would have to.

• For example: we could just suppose that

there were some other factors at work. If that is the case then Newton’s theory is unfalsifiable and hence not scientific.

• Kitcher: we could state that Newton’s

theory contains a series of supplementary assumptions that would cover all eventualities and keep it falsifiable.

• But anyone could do this for any theory, so it doesn’t work.

Example • The core claims of Newton’s theory are not falsifiable by themselves, but only with supplementary claims.

• Similarly, I can claim that Magic is not

falsifiable by itself, but can be made so by the addition of supplementary claims that entail observational consequences.

• e.g. If Magic is true, then grass is green and animals exist, etc.

• The moral of this story is that once you

have to add observational consequences to a theory, you can do this for any theory, and we are back where we started with no distinction between science and the rest.

A Response: Holism • Popper assumed that individual claims or

small groups of claims (like Newton’s laws) have observational consequences.

• But what if individual scientific claims do not confront the evidence one by one, but in large groups?

• This is called Holism.

The Duhem/Quine Thesis

• Holism abandons the idea that we can

isolate precisely where a theory has gone wrong.

• If a theory faces contrary evidence, there is always a choice about which statements of the theory which must be revised.

• More than one theory can “fit the facts”. • We just tend to make the easiest revisions.

An Atomist view of Falsification Claims made by the Theory

Falsifying Evidence

In this case we know exactly which claim was wrong

A Holist view of Falsification Claims made by the Theory

Falsifying Evidence

Any claim may be singled out as the “wrong” one.

Example • Kitcher: Newtonian mechanics was falsified by the orbit of Uranus.

• Scientists had a choice: propose some

unseen influence and keep the theory, or abandon it.

• They chose to keep it in defiance of their observations.

• Why? Because it was simply the most useful theory they had.

• Kitcher: there are a variety of reasons why some revisions are better than others.

• Some revisions are testable independently of the theory (like the existence of Neptune).

• Some revisions are more unified than others (more coherent).

• Some revisions are more useful in getting us to ask new questions.