Stalnaker and Lance on ImportExport (IfAnd)
Branden Fitelson
October 12, 2004
Stalnaker and Lance (S&L) give what they claim to be a counterexample to the probabilistic
importexport law (what Bennett calls “IfAnd”). This is the principle which says that
Pr
A
B
C
Pr
A
&
B
C
Note: given The Equation (which is
assumed
in this context), this is equivalent to
Pr
C A
&
B
Pr
A
C B
Bennett discusses the example of Stalnaker and Lance in
§
40.
I think his response is
inadequate, and I also think the analyses of S&L and Bennett are incorrect. However, I
think there is a way to bolster the argument of S&L (for a slightly di
ff
erent conclusion).
Below, I will present their analyses, along with my commentary
/
alternative analysis.
The Example
: There are 2 urns containing 100 balls each with the following constitutions
Urn 1: 90 red iron balls and 10 green copper balls
Urn 2: 90 green iron balls and 10 red copper balls
Agnes picks an urn at random, draws a ball (
a
) out, and returns the ball without noting
its color or composition. Then she draws a second ball (
b
) from the same urn. Let
Ra
: the first ball she picked was red.
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 Fall '06
 FITELSON
 Logic, Conditional Probability, Probability theory, Bayesian probability, Gbq Ñ Cbq

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