Karl Popper (1902-1994)
Demarcation between science and non-science
Zoltán Dienes
What is science?
What is the difference between science and pseudo-science?
What is the difference between good science and bad science?
On what grounds should some papers submitted to scientific journals
be rejected or accepted?
Are Christian Science, Creation Science, Scientology, astrology,
Traditional Chinese Medicine sciences? If not, why not and why
does it matter?
Is psychology a science? Good science or bad science?
How does knowledge grow?
Knowledge only grows by critical discussion
Traditionally: schools of thought aim to impart a
doctrine pure and unchanged
Critical tradition: Propose a conjecture then ask your
students to try to do better. All knowledge is provisional
and thus should always be open to criticism.
But as for certain
truth no man has
known it
For all is but a woven
web of guesses
Xenophanes 500 BC
“If an otherwise highly intelligent patient rejects a suggestion on not
too intelligent grounds, then his imperfect logic is evidence for the
existence of a … strong motive for his rejection” FREUD
“If an otherwise highly intelligent patient rejects a suggestion on not
too intelligent grounds, then his imperfect logic is evidence for the
existence of a … strong motive for his rejection” FREUD
You are an analyst and the patient’s dream content suggests a classic
interpretation: A paranoid male patient dreams of being hit by a
man with a large stick. The dream symbolises unconscious homoerotic wishes.
If the patient accepts the interpretation, you conclude it was correct.
If the patient strongly rejects it, on the grounds he is obviously
perfectly straight, you conclude the interpretation was correct.
“If an otherwise highly intelligent patient rejects a suggestion on not
too intelligent grounds, then his imperfect logic is evidence for the
existence of a … strong motive for his rejection” FREUD
You are an analyst and the patient’s dream content suggests a classic
interpretation: A paranoid male patient dreams of being hit by a
man with a large stick. You conclude that the dream symbolises
unconscious homo-erotic wishes.
If the patient accepts the interpretation, you conclude it was correct.
If the patient strongly rejects it, on the grounds he is obviously
perfectly straight, you conclude the interpretation was correct.
What do you think of this strategy for establishing the correctness of
dream interpretations?
Why do people often prefer the food they were brought up on, but
not always?
Theory:
Factor 1: We are programmed to like familiar things (e.g. foods, people,
animals, tools, etc) because our knowledge and skills are likely to
apply to them. They are not dangerous, we can deal with them. Thus,
there is a mechanism that automatically makes us like things as we
come across them more often.
Factor 2: But we also get bored with familiar things, because there is
little to learn from them and we have a drive to learn.
These two factors act in opposition to each other.
Call this the two factor theory.
An experiment is conducted with people given increasing exposure
to a new taste, taste x, and the participants’ liking of it is
measured at 3 time points.
Results:
People’s liking increased across all time points.
Explanation: Liking increased because the increasing familiarity
indicated the taste was safe (first factor operating)
Results confirm theory.
Another experiment is conducted with people given increasing
exposure to another new taste, taste y, and the participants’ liking
of it is measured at 3 time points.
Results:
People’s liking decreased across all three time points.
Explanation: Liking decreased because participants got bored
(second factor operating)
Results confirm theory.
Another experiment is conducted with people given increasing
exposure to taste z and the participants’ liking of it is measured
at 3 time points.
Results:
People’s liking first increased then decreased
Explanation: The first factor operates initially before boredom
becomes stronger
Results confirm theory.
Another experiment is conducted with people given increasing
exposure to a new taste and the participants’ liking of it is
measured at 3 time points.
Results:
People’s liking first decreased then increased
Explanation: Boredom operates initially before the first factor
becomes stronger
Results confirm theory.
So increasing people’s exposure to a new thing can:
1. Increase people’s liking because the familiarity means it is safe
(first factor operating)
2. Decrease peoples liking because they get bored (second factor
operating)
3. First increase then decrease liking because the first factor
operates initially before boredom becomes stronger
4. First decrease then increase liking because boredom operates
initially before the first factor becomes stronger
The theory is a good one because it explains all these outcomes.
Discuss.
Popper 1934:
The empirical content of a theory increases with its degree of
falsifiability.
The more a statement forbids, the more it says about the world.
A theory that forbids many outcomes is easy to falsify – it asserts
a lot about he world.
A theory that allows everything explains nothing.
Outcomes allowed by theory 1
All conceivable outcomes
Outcomes allowed by theory 2
Theory:
In human beings, the hippocampus is required for spatial
navigation.
You find Sam who, due to a recent unusual viral illness, has
destruction of all his hippocampus and no other brain structure. His
spatial navigation is very bad.
Have you established the theory is true?
In human beings, the hippocampus is required for spatial
navigation.
What about if you found 20 teenage drivers who all destroyed their
hippocampi (and no other brain structure) in car accidents. Their
spatial navigation is very bad.
Have you established the theory?
Theory:
In human beings, the hippocampus is required for spatial
navigation.
Your 21st teenage driver with complete destruction of the
hippocampus has excellent spatial navigation.
What can you conclude?
No amount of evidence ever shows a general theory is true.
Scientific theories are never conclusively established.
But evidence can show a theory is false.
We should be happy when our theories are falsified: We learn more
from negative evidence than positive evidence!
Darwin’s theory of Evolution: Is it science?
“Some variations are copied to next generation; others are not
depending on circumstances.”
Popper: You cannot predict the course of history, evolutionary or
otherwise. The theory is not falsifiable, so not a scientific theory
per se.
(Yet it is scientifically invaluable because of testable theories it
helps generate: It is a “metaphysical research programme”.)
But Darwinian evolution as an explanation of life on earth would be
wrong if:
Age of earth was as young as it was thought when Darwin proposed
his theory;
There was no continuity of anatomy and physiology and especially
genetics between all life, yet the continuity is staggering;
The fossil record did not show the age dependent changes that it
does overall.
Contrast:
“God created life according to his wishes”
Can produce any pattern in fossil record, physiology anatomy
and genetics, and is compatible with any age of the earth
The Open Society: The essence of science - and democracy
Popper argued that posing the problem for a political system to
solve as "how to choose the best leader" is ill conceived,
because we cannot know who is the best leader, just as we
cannot know if we have a true scientific theory.
NO system guarantees the best or even a good leader,
least of all the alternatives to democracy
Science does not guarantee that we find the best of all theories, it
only allows us to remove a theory by rational criticism (rather
than force).
Democracy does not guarantee that we select the best of all
leaders, it only allows us to remove a faulty leader by rational
criticism rather than force.
In science any one can in principle advance an argument that
influences a fate of a theory;
in a democracy any one can in principle advance an argument
that influences the fate of a leader (party or government) - by
books, newspaper letters, blogs, etc.
I argue that
Tibetans ruled
Tibet until 1950;
we have a right
to self rule
Girl arrested for
“offensive” t-shirt what is happening to
the Open Society in
the UK?
Tibet has always been
part of China; nobody
may challenge that
history as determined by
the government; to do
so is Treason
In science all relevant information useful for evaluating a
theory should be publically available;
in a democracy all relevant information useful for evaluating a
leader (as a leader) should be publically available.
I deeply regret
introducing the
Freedom of
Information Act
Leaders, of course, don’t like Open Societies…
“checks and balances”
hinder my power ….
transparency reveals
scandals
The scientific duty of a researcher is to criticise theories just
as the patriotic duty of a citizen is to criticise their leaders.
(Governments will often use the excuse of patriotism to
argue the opposite, in order to save their hold on power.)
If you criticise me
you don’t love
your country!
The essence of both science and democracy is the open
society
i.e. the society that actively encourages the critical tradition
in a way that allows theories and leaders to be discarded by
reason rather than bloodshed.
We as scientists should resist the influence of any politics
promoting a closed society …
such influence contradicts the core of our beings as scientists
Benjamin Franklin: “Those who desire to give up freedom in order to gain
security will not have, and nor do they deserve, either one”
Popper 1934:
Bold ideas, unjustified anticipations, and speculative thought are our
only means for interpreting nature.
Those among us who are unwilling to expose their ideas to the
hazard of refutation do not take part in the game of science.
WHEN YOU DO YOUR PROJECT:
How would you know if your favourite theory were wrong?