Sir Karl Popper, part III

1
Sir Karl Popper, part III

• October 15, 2008

2
Introduction

• Last time need confirmation to explain why we
  should accept certain basic statements and not
  others.
• Problems with probabilistic theories.
• Problems with prediction.

3
Probabilistic Problems

• Theory The chance of heads is ½.
• Q Do any observations deductively refute this
  theory?
• Example Mendels Peas.

4
Peas can be wrinkled or round. Hypothesis One
gene controls for this feature. Dominant allele
is round (R), recessive allele is wrinkled
(w). Test start with all Rw peaplants, and
observe their offspring. Result 556
offspring433 round 76133 wrinkled 24
5
Prediction Problems
Problem of Rational Prediction What is the
rational basis for preferring one unrefuted
generalization to any other?

• Observations (basic statements) alone dont let
  us predict anything.
• Observation generalized theory does allow
  prediction.
• Example
• This is a salt.
• If this is a salt then it will dissolve.
  --------------------------------------------
• Thus, this salt will dissolve.

Basic Statement
Generalization
6
Poppers Answer

• Choose the most corroborated theory.

Salmons Response

• This doesnt make any sense.

7
Salmons Response

• Corroboration doesnt have anything to do with
  future success.
• If it did, then it would be a form of induction
  inferring future success from past performance.
• But Popper doesnt believe in induction.
• Q If corroboration has nothing to do with future
  success, then why use it as a guide to prediction?

8
Poppers Rejoinder

• Example
• You are faced with two hypotheses, h1 and h2.
• You have to decide between them.
• Lets say that they are equally bold, equally
  broad, etc.
• What else could you appeal to when making your
  decision but corroboration?

9
Salmons Response

• Corroboration may be a theoretical virtue.
  Perhaps corroboration is even good for picking
  out the best explanatory theories.
• But this does not show that corroboration is a
  guide to a good predictive theory.

10
Popper

• I regarded (and I still regard) the degree of
  corroboration of a theory merely as a critical
  report on the quality of past performance it
  could not be used to predict future
  performance.When faced with the need to act, on
  one theory or another, the rational choice was to
  act on that theoryif there was onewhich so far
  had stood up to criticism better than its
  competitors had why? Because there is no
  better idea of rationality than that of a
  readiness to accept criticism. Accordingly, the
  degree of corroboration of a theory was a
  rational guide to practice. (124)

11
Salmons View of Popper

• Popper is a realist.
• Believes that nature has consistent regularities.
• Corroboration is a good guide that your theory
  was a true description of past experiences.
• If your theory is corroborated, then your theory
  was true of the past, and since nature is
  consistent, it is a good theory for prediction.

12
My (tentative) View of Popper

• Normally, we think that a rational guide to
  prediction is a guide to future success.
• Salmon shows us that corroboration is not a guide
  to future success.
• But, perhaps Popper doesnt think that there is a
  reliable guide to future success.
• Nevertheless, there could still be a rational
  choice choose the most corroborated theory.
• On this view a rational guide to prediction is
  not (necessarily) a reliable guide to prediction.

13
General Moral

• Popper is pressured on many sides to embrace some
  sort of confirmation
• 1. For basic statements
• 2. For probabilistic theories
• 3. For rational prediction