Title: Sir Karl Popper, part III
1Sir Karl Popper, part III
2Introduction
- Last time need confirmation to explain why we
should accept certain basic statements and not
others. - Problems with probabilistic theories.
- Problems with prediction.
3Probabilistic Problems
- Theory The chance of heads is ½.
- Q Do any observations deductively refute this
theory? - Example Mendels Peas.
4Peas 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
5Prediction 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
6Poppers Answer
- Choose the most corroborated theory.
Salmons Response
- This doesnt make any sense.
7Salmons 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?
8Poppers 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?
9Salmons 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.
10Popper
- 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)
11Salmons 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.
12My (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.
13General 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