Lecture 3 Inductive and Abductive Arguments

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Lecture 3 Inductive and Abductive Arguments

• Li Jianhui
• ljh98_at_sina.com
• http//philosophy.wisc.edu/li

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Two Gambling Strategies

• The extreme conservative This individual refuses
  to wager unless winning is a sure thing.
• Its virtue He will never loose a gamble
• its limitation there are gambles he will decline
  that he could have won.
• The thoughtful risk taker this individual at
  times enters into risky gambles hoping to win.
• Its virtue it can lead him to win wagers by
  taking risks
• its limitation he can loose money.

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Two Gambling Strategies

• Limiting to deductive arguments is a conservative
  strategy.
• The virtue you avoid the risk of reaching false
  conclusion from true premisses
• The limitation you decline to say anything that
  goes beyond the evidence.
• Nodeductive arguments are riskier.
• The gain you can reach true conclusion that go
  beyond what the premisses say
• The risk you may reach false conclusion from
  true premisses.

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Science is a risky business

• In science as well as in everyday life, we make
  nondeductive inference all the time. We often are
  prepared to take risk.
• Scientists often try to reach conclusions about
  universal laws.
• When scientists conclude that a universal law is
  true or probably true, based on premisses that
  describe the observations they have made, they
  arent making a deductively valid argument.

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Science is a risky business

• Science is a very ambitious enterprise. Science
  ventures beyond what strictly observed in the
  here and now, just as the conclusion in a
  nondeductive argument ventures beyond the
  information strictly contained in the premisses.
• Detective work is also taking risk.
• There are two sorts of nondeductive inference
  indeductive and abductive.

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Induction

• Inductive inference involves taking a description
  of some sample and extending that description to
  items outside the sample. E.g. 60of the county
  voters called are democrats.?About 60 of the
  county voters are democrats.
• Inductive strength is not a yes/no matter
  arguments are either stronger or weaker.
• Two factors influence inductive strength
• Sample size
• Representativeness or unbiasedness of the sample

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Abduction

• Inference to the best explanation. E.g. Mendels
  theory of genetic factor.
• A set of observations doesnt deductively imply a
  theory
• But a theory deductively implies some
  observations. This corresponds more closely to
  what Mendel did.
• So a better representation of Mendels inference
  might go like this The theory entailed a
  prediction the prediction came true hence the
  theory is probably true. Note that this argument
  is not deductively valid (the logical form is on
  page 27). Successful prediction isnt absolutely
  conclusive proof that the theory is true.
• On the other hand, if the predictions entailed by
  Mendels theory had come out false, that would
  have followed him to deduce that the theory is
  mistaken. That is a failed prediction is
  conclusve proof that the theory implying the
  prediction is false.

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Abduction

• The surprise principle
• An observation O strongly supports H1 over H2 if
  both the following conditions are satisfied, but
  not otherwise (1) if H1 were true, O is to be
  expected and (2) if H2 were true, O wouldnt
  have been expected.
• The surprise principle explains why success of
  safe predictions provides less compelling
  evidence than the success of daring
  predictions.
• The only game in town fallacy
• If you dont want to accept my explanation about
  something, you must produce a more plausible
  explanation of your own. If you cant, you have
  to accept my explanation. Now we commit an
  abductively fallacy the Only Game in Town
  Fallacy.
• Abduction is sometimes described loosely as
  follows if a theory expains some observation,
  and if no rival account is available that can do
  a better job of explain it, then you should
  accept the theory. Although this description of
  abduction is roughly correct, it makes the
  mistake of sanctioning the Only Game in Town
  Fallacy. The fact that no rival account is better
  than the explanation I conduct doesnt show my
  explanation is even minimally plausible.