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notes_11 - Notes on KAIL/15/06(B.F This is a very long...

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Unformatted text preview: Notes on KAIL Chapter 10 11/15/06 (B.F.) This is a very long, technical, and difficult chapter. There is no hope of going through it all in one seminar. Instead, my comments (and Mike’s comments) will focus on a few issues that are central to TW’s discussion in the chapter. Let’s begin by recalling TW’s explication of “ E is evidence for H for S ”, which we have already discussed in our last meeting: (EV) E is evidence for H for S iff E is included in in S ’s body of evidence and Pr (H | E) > Pr (H) . Last week, we discussed the first component of (EV) — the “inclusion in S ’s body of evidence” component. This week, we will focus on the second component — the “support as positive probabilistic dependence” component. There are many important questions that must be answered in order to get a handle on the intended sense of this second component. Here are five: 1. What kind of probability function is TW’s “evidential” probability function Pr? • Pr (p) is clearly not S ’s actual degree of belief (credence) in p [Pr ≠ C a ]. For one thing, S ’s actual degrees of belief C a can be crazy (even incoherent ), and we want Pr to ground non-crazy claims about evidential support [although, it’s not entirely clear why we want this from a traditional epistemological point of view, which cares about full belief and knowledge — see question (3), below, for further discussion of that issue]. Moreover, as we mentioned last week, if S ’s credence in either H or E happens to be extreme (zero or 1), then E and H cannot be positively dependent on C a . And, surely, S can actually have extreme credences in either E or H , for any E / H . As such, identifying Pr and C a would basically trivialize TW’s “support” relation. Finally, TW wants his “support” relation to be objective , and identifying Pr and C a would make it patently subjective in a way TW doesn’t want. • Pr (p) is not even to be identified with the ideally rational or justified degree of belief (for S ) in p [Pr ≠ C j ]. TW says that this “comes closer” to what he has in mind with his “evidential” probability. For one thing, at least C j is objective in ways that C a is not. For instance, even if S happens to have extreme degree of belief in E or H , it might be that this is irrational or unjustified (given everything S knows). Moreover, C a might even be incoherent , whereas (presumably) C j cannot be. This gives C j a kind of objectivity (and also probative force) that seems to be required to undergird TW’s objective “support” relation. However, TW wants to think of “support” as an objective relation between E and H [and some “background corpus” K — see question (4) below]. But, if we identify Pr with C j , then we can still get undesirable verdicts about “support”, because an agent (albeit an ideally rational one) is “getting between” E and H . For instance, there may be cases in which C j (E) = 1, but we still want to say that...
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notes_11 - Notes on KAIL/15/06(B.F This is a very long...

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