j. blackmon. biographical highlights the problem of demarcation inductivism falsificationism ...

KARL POPPER’S FALSIFICATIONISM

J. Blackmon

Outline

Biographical Highlights The Problem of Demarcation

Inductivism Falsificationism

Problems for Falsificationism

Brief Bio

Karl Popper 1902-1994 Austrian-British Known for

falsificationism, critical rationalism.

The Logic of Scientific Discovery

Rejected the popular interpretation of QM

The Problem of Demarcation

What distinguishes science from pseudo-science and, in general, from non-science?

One answer came from logical positivism and empiricism: The inductive method, hypothetico-

deductivism. Hypotheses are confirmed (not proven) when their logical consequences turn out to be true. Confirmation confers more reason to believe something.



Popper: “But this did not satisfy me…” This is an understatement. Popper holds that confirmation is a myth. That is to say that hypotheses are not

given more justification when their logical consequences turn out to be true.


The following form

1. H P2. P3. Thus, H

is a logical fallacy. Everyone knows this. The H-D method was never supposed to offer a guarantee.

But it was supposed to show how, as more observations came in, a hypothesis might become better confirmed.

This is what Popper rejects. In addition to being logically fallacious, it’s not good science.


1. H1 P

2. P3. Thus, we have more

confirmation of H1

According to H-D, each time a prediction, P, is observed, H gets more confirmation.

But as Popper insists, and as everyone else knew, H1 could be false, and yet P occurs for some other reason.

There’s always some H2 or H3 (and so on) that also predicts P. And there are infinite alternatives to H1.


Also, we are subject to confirmation bias. Confirmation Bias: The tendency to fixate

on and emphasize data that confirms one’s prior beliefs while ignoring or dismissing counter-evidence.

While the term, confirmation bias, is not Popper’s, he is distinctly aware of its power.


Also, we are subject to confirmation bias. Popper: “Confirmation is everywhere.” But while people are inclined to see this

as a good thing, this is only an illusion. The more easily a theory can be

confirmed, the more trivial and less scientific it is.


Example: Freudianism The parent who

strikes the child in anger confirms the Freudian’s belief in an id, while the parent who refrains from striking in anger instead confirms the Freudian’s belief in a counter-acting super-ego.


Example: Freudianism This is not good

news for Freud’s theory!

The Freudian sees confirmation everywhere.

But this is not reason to think observation supports the theory…


Example: Freudianism Instead, it’s reason

to think the theory rules our hardly any observations.


Other Examples Astrology Adler’s Psychology Marxism

Such theories were not good scientific theories because they rule out nothing or very little.

Hardly any observation could falsify them.


Imagine the weather prediction: Tomorrow we will have rain, or not.

Or the astronomer saying: Last night’s comet will reappear tonight somewhere in the northern hemisphere…


Thus Popper is an inductive skeptic. As he sees it, David

Hume proved there could be no logic of inductive reasoning.

No number of confirming instances can justifiably increase our confidence in a theory.


Thus Popper is an inductive skeptic. Popper is not

simply a fallibilist. Fallibilism: We can

never be completely certain about matters of fact.

He is an unabashed inductive skeptic.



Popper’s Answer: Falsificationism demarcates the scientific theories from the rest. Falsificationism: A hypothesis is scientific

if and only if it has the potential to be refuted by some possible observation.

A hypothesis is bold to the extent that it risks falsification.


The following form

1. H P2. ~P3. Thus, ~H

is logically valid.

(~ is the symbol for not.)

We do make scientific progress, but not by confirming hypotheses. We aggressively

attempt to refute our hypotheses.

We learn more and more, as time goes on, what’s false.


The Holy Grail Analogy Imagine that there are infinite grails: all

of them glow for a while, but only the Holy Grail glows forever.

If you have a glowing grail, you know you might have the Holy Grail.

If it stops glowing you know you don’t have the Holy Grail, and you can drop it and look for a new glowing grail.

But you never know if you have the Holy Grail.


The Holy Grail Analogy There are infinite scientific hypotheses,

but only the true one will never be falsified.

If you have and unfalsified hypothesis, you know you might have the truth.

If it is falsified, you know you don’t have the truth, and you can drop it and look for a new hypothesis.

But you never know if you have the truth.


The Holy Grail Analogy Hypothesis :: grail Glowing :: being

unfalsified Holy Grail :: True

Hypothesis Ceasing to glow ::

falsification

Blackmon: This analogy could

be better. Godfrey-Smith

writes that we carry the grail around.

But the knights should be vigorously testing the grails.


Popper on Scientific Change Stage 1: Conjecture: Offer a hypothesis H

that might describe and explain something about the world. A good conjecture is a bold one, one that takes risks.

Stage 2: Attempted Refutation: Subject H to critical testing in an attempt to show that H is false. Once H is refuted, go back to Stage 1.

One prohibition…


Popper on Scientific Change One prohibition: If H predicts P and H is

refuted by the observation that ~P, then you cannot offer an H* in Stage 1 that differs from H only in not predicting P.

In other words, you cannot make isolated excuses for your hypothesis.

No ad hoc revisions to your hypothesis.


Popper on Scientific Change One prohibition: No

ad hoc revisions! Otherwise, you may

have once had a scientific hypothesis, but you are no longer following a good scientific methodology.

Anthony Flew’s Invisible Gardener H: A gardener tends

this area. P: Within a few days,

we’ll see a gardener. But instead, we

never see a gardener.

H has been falsified.


Popper on Scientific Change One prohibition: No

ad hoc revisions! Otherwise, you may

have once had a scientific hypothesis, but you are no longer following a good scientific methodology.

Anthony Flew’s Invisible Gardener Ad hoc revision, H*:

An invisible gardener tends this area.

Popper will cry foul here.

The new hypothesis should be bold, not a retreat.


Popper on Marxism Marxist

Conjecture: Industrialized capitalist societies will experience a proletarian revolution and become socialist states.


Popper on Marxism Originally, Marx’s

conjecture counted as a scientific hypothesis—at least if we put a time limit on it.

It is falsifiable.


Popper on Marxism Falsifiable: Just

wait and see if (within a generation or whatever) the revolutions occur.

If not, the hypothesis is falsified.


Popper on Marxism So far, so good. However, what did

Marxists do when no such revolutions occurred after a period of time?

They did not treat Marxism as refuted.


Popper on Marxism Instead, according

to Popper, they made an ad hoc revision.


Popper on Marxism H*: Industrialized

capitalist societies will experience a proletarian revolution and become socialist states, unless welfare appeases the people.


How does Albert Einstein’s General Theory of Relativity fare?

Objections and Problems

How do we recognize falsification? Logically, observing an A that is a non-B

falsifies the conjecture All As are Bs.

Example Conjecture: All pieces of iron expand

when heated. Falsifier: any observation of a piece of

iron which does not expand when heated.


How do we recognize falsification? But suppose you observe what you took

to be iron contracting when heated. Should you treat the conjecture as

refuted? How can you be sure that instead this is

not iron after all? How can you be sure that your

measurements of the contraction and the temperature are accurate?


How do we recognize falsification?

Generally Maybe the conjecture that All As are Bs is

true, but our belief that we are observing a falsifying instance (an A that is a non-B) is false.



Recall Quine’s point about holism about testing and the Duhem-Quine thesis: No statement is testable in isolation.

When we observe the unexpected, instead of rejecting the hypothesis, we can reject one of the background assumptions.

We can even reject the description of the observation itself.



Example Conjecture: The

universe is 13.8 billion years old.

Falsifier: The “Methuselah Star”, HD 140283, is 14.5 billion years old.



Example Astronomers did

not reject this conjecture.

They re-examined their measurement of HD 140283.



Example Rejecting the

conjecture in this case would seem rash.

What can Popper say?


How do we recognize falsification? Here’s what Popper can’t say:

We should try to maintain our most confirmed hypotheses. If we have more reason to believe the universe is 13.8 billion years old, then we suspect the hypothesis that HD 140283 is 14.5 billion years old. If instead, the age of HD 140283 is more confirmed, then we suspect the hypothesis about the age of the universe.


How do we recognize falsification? Popper can’t say this because he rejects

confirmation. An inductivist can handle the problem of

holism about testing because the inductivist is committed (right or wrong) to the idea that some hypotheses can be more confirmed than others. Whenever there is a question about which one to reject, we can choose accordingly.

Popper appears to have no such option.


How do we recognize falsification? Popper admitted that the other

assumptions were also conjectures which might be false.

He also admitted that logic could never force one to reject a conjecture instead of rejecting some background assumption.

Popper held that a good scientist would not reject background assumptions just to protect a conjecture.


How do we recognize falsification? Popper also admitted that we cannot be

certain about a reported falsifier. His answer is that the scientist must

make a decision about whether to accept the report or not.

Godfrey-Smith finds that Popper has retreated from using logic to demarcate science from pseudo-science.


How do we recognize falsification? Godfrey-Smith finds that Popper has

retreated from using logic to demarcate science from pseudo-science.

Popper appears to rely more and more on method than on pure logic.


Falsificationism cannot recognize nontrivial probability attributions as scientific. Conjecture: Event E has a probability of

0.0001. This has no falsifier.


Falsificationism cannot recognize nontrivial probability attributions as scientific.

Example: If a coin is fair, then the probability of Heads 100 times in a row is extremely low. But it is still possible. Observing 100 Heads in a row doesn’t

falsify the conjecture that the coin is fair. Are such conjectures really unscientific?


Falsificationism cannot recognize nontrivial probability attributions as scientific. Popper agreed that logically speaking all

such hypotheses are unscientific. However, in practice, the scientist can

decide on thresholds at which nontrivial probability attributions are treated as 0 and 1.

In a given experiment, you might treat a probability less than 0.0001 as just 0.0.

This is falsifiable.


Falsificationism cannot recognize nontrivial probability attributions as scientific. Godfrey-Smith holds that, as before,

Popper has retreated from using logic to demarcate science from pseudo-science.

Popper is now relying on “good scientists” making judgment calls.


The Bridges Problem Suppose we are

going to build a bridge, and we are to choose between two theories, H1 and H2, which determine different ways of building a bridge.


The Bridges Problem H1 has been tested

many times and had passed every test.

H2 is a brand new conjecture which has never been tested.

Neither H1 nor H2 has been falsified.

Would it be irrational to use H2 to build the bridge?


The Bridges Problem Would it be

irrational to use H2 to build the bridge?

Popper never says we have more reason to use H1.

But he does say that H1 is more corroborated.


The Bridges Problem But he does say

that H1 is more corroborated.

In such cases, it is rational to choose the more corroborated theory.


The Bridges Problem So, what is corroboration? Is it just confirmation or not? If it’s confirmation, then Popper has

relinquished his heroic stance against inductivism.

But if it’s not confirmation, then how does it help us determine whether to use H1 or H2?


Popper’s Dilemma Either corroboration is like confirmation in that

it gives us more reason to prefer corroborated theories over uncorroborated theories, or corroboration is not like confirmation and cannot be regarded as any guide to truth. [68]

If the former, then Popper can answer the Bridge Problem, but he has relinquished his inductive skepticism.

If the latter, then who cares if a theory is corroborated?


Godfrey-Smith’s Analogy

The transcript is merely a record of what you have done.

The transcript is like corroboration in this sense: it is backward-looking.

The letter of rec usually covers both what you have done and what you are likely to do.

The letter is more like confirmation.


Popper’s Dilemma It appears that Popper caught between

saying that we have no good reason to expect one hypothesis about bridge-building to work no matter how corroborated that theory is, or admitted that his view is in some sense “inductivist”.

Popper appears to be in a problematic position.


Alternatives Hypothetico-Deductive Method Strong Inference


Alternatives: Hypothetico-Deductive Method1. Generate a hypothesis, H.2. Deduce observational predictions, P,

from H.3. Test to see if these predictions come out

true.4. If they do, the H gains support.5. If they do not, H should be rejected.6. Return to Step 1.


Alternatives: Strong Inference Godfrey-Smith calls

this the “Sherlock Holmes” method.

Holmes called his reasoning deductive.


Alternatives: Strong Inference While philosophers

point out that most of his reasoning was inductive, his overall method often took the form of the process of elimination.

In that sense, it was deductive.


Alternatives: Strong Inference Identify all possible

hypotheses and their individual predictions.

Critically test them, rejecting each one until the last one is standing.


Alternatives: Strong Inference Popper’s reply? Popper argues that

there will always be infinite other theories to choose from.

We can eliminate, but we can’t narrow it down.

j. blackmon. biographical highlights the problem of demarcation inductivism falsificationism ...

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