|Jackson, Frank C.
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Frank C. Jackson
|Conditional||Lewis V 153
Conditional/Grice/Lewis: if P (A > C) is high because P (A) is low (> ex falso quodlibet), what is then the meaning of "If A, then B"? Why should one not say the strongest: that it is almost as likely as not A?
JacksonVsGrice/JacksonVsLewis: we often claim things that are much weaker than we could actually claim, and this for a good reason.
I assume that your belief system is similar to mine, but not completely equal.
E.g. Suppose you know something what seems to me very unlikely today, but I would like to say something useful anyway. So I say something weaker, so you can take me at any rate at the word.
Lewis V 153
Definition robust/Jackson/Lewis: A is robust in relation to B, (with respect to one's subjective probability at a time) iff. the probability of A and the probability of A conditionally to B are close, and both are high,...
...so if one learns that B still considers A to be probable.
Jackson: the weaker can then be more robust in terms of something that you think is more unlikely, but still do not want to ignore.
If it is useless to say the weaker, how useless it is then to assert the weaker and the stronger together! And yet we do it!
E.g. Lewis: "Bruce sleeps in the clothes box or elsewhere on the ground floor".
Jackson: Explanation: it has the purpose to assert the stronger and the same purpose to assert the more robust. If both are different, we assert both.
Robustness/indicative conditional/Lewis: an indicative conditional is a truth-functional conditional, which conventionally implies robustness with respect to the antecedent (conventional implicature).
Therefore the probability P (A > C) and P (A > C) must both be high.
This is the reason why the assertiveness of the indicative conditional is associated with the corresponding conditional probability.
F. C. Jackson
From Metaphysics to Ethics: A Defence of Conceptual Analysis Oxford 2000
Die Identität von Körper und Geist Frankfurt 1989
Konventionen Berlin 1975
Philosophical Papers Bd I New York Oxford 1983
Philosophical Papers Bd II New York Oxford 1986
Cl. I. Lewis
Mind and the World Order: Outline of a Theory of Knowledge (Dover Books on Western Philosophy) 1991