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Topics• The Amazing Power of Science – A Very Brie
f Reflection• Science & Pseudoscience – Popper’s Dem
arcation Criterion• Comments on Popper’s Falsificationism• Hypothesis & Evidence• Criteria of Adequacy• Further Example: Evolution vs. Creationism
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The Amazing Power of Science – A Very Brief Reflection
• Influence every aspect of our lives tremendously.
• Change the world with an exceedingly fast pace.
• Produce scientific knowledge with astounding breath and depth.
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Science & Pseudoscience – Popper’s Demarcation Criterion
• About 100 yrs ago, people were deeply interested in theories like:
• Alfred Adler’s (1870-1937) individual psychology:
– An inborn sense of inferiority
– Strive for superiority
– Seemed to be able to explain everything within its field of inquiry!
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• Albert Einstein’s (1879-1955) theory of relativity:
– Relativistic spacetime e.g. simultaneity is relative.
– E = mc2
– One of the two pillars of modern physics.
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• Both claimed to be “scientific”. – “Science” signifies __________,
___________, ___________.
• Yet, Karl Popper (1902-1994) held that theories like Alder’s is actually not scientific.
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• He raised the demarcation problem:
– When should a theory be ranked as scientific?
– Is there a criterion for the scientific status of a theory?
Scientific / Pseudoscientific
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• His criticism of theories like Adler’s:
– Adler’s theory could easily “explain” two “diametrically opposite” cases, e.g.:
• A man pushes a child into the water with the intention of drowning it.
• A man sacrifices his life in an attempt to save the child.
– How?• By appealing to the idea of inferiority
feeling, . . .
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– Its “explanatory power” is just a disguise of its “interpreting power”.
• Points for analysis in your paper, e.g.: How is this interpreting power harmful to a theory? (Hint: meaning shift of some key concepts)
– This apparent strength - capable of explaining everything - is in fact a weakness.
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– Arthur Eddington’s confirmation (1919) of Einstein’s theory was different:• The light-bending prediction• Might be refuted — not always confirmatory!
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• Consequently, Popper proposed:
– The criterion of the scientific status of a theory is its
falsifiability, or refutability, or testability.
• Is this criterion adequate?
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Comments on Popper’s Falsificationism• Two senses of falsifiability:
• Falsifiability as a logical property of statements
– Falsifiable, e.g.:“It never rains on Wednesdays.”“All substances expand when heated.”
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– Unfalsifiable, e.g.:“Luck is possible in sporting speculation.”“There is a ghost in this room which cannot be sensed, directly or indirectly.”
• Falsifiability as a methodological prescription of how scientists should act
– E.g. try to make “all substances expand when heated” unfalsifiable in this sense.
• But both these senses are problematic!
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• 1. The logical sense– Too _______
– Suppose T is a theory having testable predictions.
– Let C be, say, “there is a ghost in this room which cannot be sensed, directly or indirectly”.
– Then T & C has testable predictions and thus scientific in the logical sense!
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• 2. The methodological sense– Too ________
– E.g. the discovery of Neptune• Newton’s theory of gravitation wrongly predi
cted the orbit of Uranus – abandoned it?
• In fact, some scientists tried to rescue Newton’s theory by postulating the existence of an unknown planet.
• Neptune was finally discovered at almost the exact place and time as predicted.
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• The “failure” of Popper's criterion throws up an important question:
– Is it possible to find some common features shared by all the sciences, but not shared by anything else?
– Has science “essential features”?
• Popper assumed that the answer was yes.
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• Ludwig Wittgenstein (1889-1951) argued against essentialism.
– Family resemblance concepts like “game” have no essential features.
– Cf. His Philosophical Investigations, sections 66-7.
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A B C D E F1 ------------- -------- -------2 ------------------------------ 3 ------- ------- ------- 4 ----------------------- --------------
5 -------------- ---------------
GAMESFEATURE
S
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• The same may be true of “science”.– Note the heterogeneity of science.
• If so, no simple criterion for demarcating science from pseudoscience.
• How actually should we choose among hypotheses – scientific or pseudoscientific?
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Hypothesis & Evidence• The logic of hypothesis testing:
Main hypothesis(+ background assumptions)
I1 I2 I3
. . . . .. . . . .
deduction induction
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• Discussion - a daily example:– The problem:
• A lamp does not light up.
– Hypothesis:
– Implication:
– Test:
– Result:
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• Positive evidence does not prove conclusively that a hypothesis is correct.
– There are always competing hypotheses that have the same set of positive evidence.
I1 I2 I3
. . . . .
. . . . .
H
In
I1 I2 I3
. . . . .
. . . . .
H’
In
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• Negative evidence does not prove conclusively that a hypothesis is incorrect.
– A Modus Tollens:
(Hypothesis H • Assumptions A) Implication I
I . (H • A)
– So maybe the trouble comes from A.
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• Example:
– Columbus and the negative evidence against the flat Earth hypothesis
– Supporting the round Earth hypothesis:
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– Saving the flat Earth hypothesis:• Assumption: light travels in curved lines.
• Facts alone cannot decide which hypothesis to accept.– Criteria of Adequacy are needed.