Lecture Four Popper

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Lecture FourPopper Falsificationism

• Dr Emma Tobin
• Philosophy
• Bristol

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Science Pseudoscience

• Science
• Physics
• Chemistry
• Biology
• Geology
• Zoology
• Ecology
• Epidemiology

• Pseudoscience
• Astrology
• Palmreading
• Graphology
• Parapsychology
• Creation Science
• Homeopathy
• Psychoanalysis
• Marxism

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Science vs. Pseudo-ScienceDemarcation Criteria

• (1) Truth
• (2) Induction
• (3) Assigning Probabilities
• (4) Explanatory Power
• (5) Testability
• (6) Falsifiability
• (7) Puzzle-Solving

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Deductive Truths

• Deductive reasoning using the tools of the
  deductive logic can generate scientific truth.
  (e.g. Aristotle/Middle Ages).
• All things seek their natural place
• The natural place of the element fire is at the
  top of the terrestrial sphere.
• ?Therefore, flames near the surface of the earth
  rise.

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Problem of Deduction

• All empirical content is already contained in the
  premises.
• There is no move made beyond the premises in the
  conclusion.
• It is difficult to test the major premise.

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Induction from pure observation

• Inductive reasoning from pure observation
  generates scientific truth (e.g. Bacon/Mill).
• Confirmation collecting positive instances.
• Iron is a metal and expands when heated
• Silver is a metal and expands when heated
• Gold is a metal and expands when heated
• ? All metals expand when heated

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Humes Problem of Induction

• How can we justify our inference that the future
  will resemble the past?
• We assume there is uniformity in nature.
• Humes sceptical problem of induction we can
  never justify this assumption based on
  observation alone.

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Karl Popper 1902-1994

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• Popper accepts Humes problem of induction.
• This does not show that scientific knowledge is
  not justified.
• Science does not depend on induction after all.
• He rejects the Baconian ideal of pure
  observation as the primary step in scientific
  enquiry.
• Observation is theory laden.

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Science vs. Pseudo-Science

• Popper sees the central problem in the philosophy
  of science as that of demarcation.
• Success in science during the scientific
  revolution and beyond led to optimism about the
  application of this method to the social
  sciences, particularly to human behaviour (e.g.
  Freudian psychology) and society (e.g. Marxism)
• Popper disagrees.
• The social sciences do not follow the same method
  as the natural sciences.

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The Social Sciences Pseudo-Science

• Inductivism championed the success of science
  based on observation of positive instances of the
  theory.
• Some theories are too general (e.g.
  Astrology/Marxism/Freudian Psychology)
• It is too easy to observe positive instances once
  we are committed to the theory.
• Unquestioned commitment to a theory is not
  scientific.

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• Example Freudian Psychology
• I may illustrate this by two very different
  examples of human behaviour that of a man who
  pushes a child into the water with the intention
  of drowning it and that of a man who sacrifices
  his life in an attempt to save the child. Each of
  the two cases can be explained with equal ease in
  Freudian terms. The first man suffered
  from repression (say of some component of his
  Oedipus complex), while the second man had
  achieved sublimation. (Popper Curd Cover 6)

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Asymmetry of Falsification Confirmation

• The problem of Induction the possibility
  (independent of how many observations we have
  made in the past) that the next instance will
  falsify a generalisation.
• We cannot conclusively justify our claim that
  All Swans are white based on past evidence.
  (e.g. There could be a black swan)
• However, a single counter-instance will falsify
  the generalisation. (e.g. observation of a black
  swan.)

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Rejection of Verifiability

• Waismann (1903) If there is no possible way to
  determine whether a statement is true then that
  statement has to meaning whatsoever.
• All the statements of empirical science must be
  directly verifiable from experience. logical
  positivists
• The falisifiability of a system (its capability
  of being refuted) is the demarcation criterion
  rather than verificability.

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Examples

• (1) It will rain or not rain tomorrow
• (2) It will rain tomorrow
• It is impossible to refute (1) so (1) is not
  empirical.
• It is possible to refute (2) so (2) is empirical.

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Eddingtons Experiment
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• Einsteins theory of general relativity light
  rays bend in a gravitational field.
• Accordingly, it was predicted that the stars
  close to the sun should appear a little away from
  the sun.
• This could not be observed in normal
  circumstances because of the light of sun.
• However, Eddington observed in a solar eclipse
  that stars close to the sun appear a little away
  from the sun.
• This bold conjecture could have been falsified by
  Eddingtons observations during the solar
  eclipse.

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Theory - laden Observation

• We cannot start with pure observations.
• Twenty-five years ago I tried to bring this
  same point home to a group of physics students in
  Vienna
• by beginning a lecture with the following
  instructions Take pencil and paper carefully
  observe and write down what you have observed!.
  They asked of course, what I wanted them to
  observe.
• Popper Conjectures Refutations 61

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Bold Conjectures

• Observation needs a definite task, an interest or
  a problem to solve.
• The hypothesis (bold conjecture) comes before the
  observation.
• Observations have to be falsifiable.

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• All swans are white (T) entails every swan is
  white (o).
• Every swan is not white (observed black swan)
  (?o)
• ? All swans are white is false (?T)

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• Light bends in a gravitational field (bold
  conjecture) (T)
• We could observe that stars near to the sun do
  not appear a slight distance from the sun (?o)
• ? Light does not bend in a gravitational field.
  (?T)
• But Eddington observed (o) (Stars near to the sun
  appear a distance away from the sun (o).
• So, is T true/confirmed?

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Corroboration

• No! Falsification can only show which theories
  are false, not which theories are true.
• A theory that survives a falsification is not
  confirmed but corroborated.
• A theory is corroborated if it was a bold
  conjecture that generated novel predictions that
  were not falsified.
• However, the scientist must always adopt the
  skeptical stance that even corroborated theories
  could be falsified in the future.

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Progress in Science?

• Early Popper - Marginal Progress.
• A theory that replaces a falsified theory is a
  better theory that the old one. The Logic of
  Scientific Discovery (1959)
• Late Popper - Yes- Increasing verisimilitude
  (truthlikeness). Hypotheses can be objectively
  measured with respect to the amount of truth and
  falsity that they imply. Conjectures
  Refutations (1963)

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• The idea of verisimilitude is most important in
  cases where we know that we have to work with
  theories that are at best approximations In
  these cases we can still speak of better or worse
  approximations to the truth.
• Conjectures Refutations 235

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How does one theory progress from its predecessor?

• Degrees of Truthlikeness -
• (1) t2 makes more precise assertions than t1
• (2) t2 explains more facts that t1
• (3) t2 explains the facts in more details than
  t1
• (4) t2 has passed tests which t1 failed.
• (5) t2 has suggested new empirical tests that
  have not been suggested before t2
• (6) t2 has unified various unrelated problems.
• The empirical content of t2 exceeds t1. t2
  achieves a
• better approximation of the truth than t1.

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Discovery Justification

• Inductivism provides an account both of the
  context of discovery (pure observation) the
  context of justification (inductive inferences
  from observation sentences).
• Falsificationism only provides an account of the
  latter (i.e.) how we test a theory. It provides
  no account of how we generate the hypothesis to
  be tested.
• The context of discovery can be a totally
  creative endeavour in falsificationism.

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Probabilistic Statements/Laws

• Probabilistic statements cannot be falsified.
• Improbable events are always possible.
• An improbable event occurring is consistent with
  the probabilistic generalisation and does not
  falsify it.

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Existential vs. Universal Statements

• Not all of the statements in science are
  universal statements (e.g. like All metals
  expand when heated).
• Some statements are existential statements which
  state that something exists (e.g. there are
  quarks/electrons/black holes/viruses etc.)
• However, there are quarksis not falsified by my
  failure to observe them.
• Falsification does not apply to existential
  statements about theoretical entities.

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Modification to a Theory

• Some theories in science appear to survive being
  falsified.
• For example, Mercurys orbit was known to be at
  odds with Newtonian theory of gravitation, but
  this fact was ignored.
• Only when Einsteins theory of gravitation came
  along was Newtons theory thereby rejected.
• Popper explains that we must distinguish between
  ad hoc and non ad hoc auxiliary hypotheses.

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The Quine-Duhem Problem

• It is impossible to test a hypothesis in
  isolation. (e.g. Newton's first law is understood
  in conjunction with his second and third laws
  the law of gravity)
• How can a bold conjecture be separated from
  contextual and auxiliary hypotheses which count
  as background assumptions of the conjecture?
• How can the scientist know that she is right in
  blaming the bold conjecture rather than the
  auxiliary hypotheses?

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Summary

• Humes problem of induction should be accepted.
• Science can proceed without induction, because we
  can infer the falsity of a theory from a
  falsifying instance of it by deduction.
• Falsification rather than confirmation demarcates
  science from pseudo-science.
• Scientific theories which survive potential
  falsifications are corroborated.
• The method of science is that of conjecture and
  refutation.

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• http//www.bbc.co.uk/radio4/history/inourtime/inou
  rtime_20070208.shtml
• John Worrall, LSE
• Anthony O'Hear, (Buckingham University)
• Nancy Cartwright, (LSE)

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Thomas Kuhn (1922 -1996)

• Kuhn rejects the common idea in both inductivism
  and falsificationism that science progresses by
  the linear accumulation of new knowledge.
• Instead he claims that science undergoes
  periodic revolutions.