Saturday, October 05, 2013

Jessica Brown on evidence and luminosity

In "Thought Experiments, Intuitions, and Philosophical Evidence," Jessica Brown introduces a problem for "evidence neutrality" deriving from Williamson's anti-luminosity arguments: evidence neutrality implies that if S has E as evidence, it is always possible for S's community to know that E is evidence, which entails the false claim that evidence is luminous. Sounds ok. Then she writes this puzzling passage:
We might wonder whether we could overcome this first problem by weakening the content element of evidence neutrality. Instead of claiming that if p is part of a subject’s evidence, then her community can agree that p is evidence, the relevant condition could be weakened to the claim that her community can agree that p is true. Although this revised version of the evidence-neutrality principle avoids Williamson’s objection that one is not always in a position to know what one’s evidence is, it faces an objection from Williamson’s anti-luminosity argument. Williamson claims to have established that no nontrivial condition is luminous, where a condition is luminous if and only if for every case a, if in a C obtains, then in a one is in a position to know that C obtains (2000, 95). There is not space here to assess the success of Williamson’s anti-luminosity argument. However, assuming that it is successful, it seems that no mere tinkering with the content element of evidence neutrality will suffice to defend it.
I'm just not seeing the problem here. The proposal we're considering is this: any time S has E as evidence, S (and/or S's community) is in a position to know that E is true. But this does not imply that any non-trivial condition is luminous. The claim that evidence is luminous would need knowledge that E is evidence on the right-hand side; the claim that truth is luminous would need no restriction to evidence on the left-hand side. Saying that evidence requires being a position to know truth looks wholly consistent with Williamson's luminosity argument. Indeed, setting aside the role of the community -- which as far as I can tell is idle in the argument Brown is considering -- it follows trivially from Williamson's own view, E=K. Notice that S's knowing that p entails that S is in a position to know that p is true; this is no violation of anti-luminosity.
Anybody see what I'm missing?


  1. This looks like a straightforward slip between knowing a truth that's evidence (and so having it has evidence) and knowing that a truth is evidence, which is like a slip between K and KK if E=K is true.

  2. Yeah, that was my first thought. But I felt like I must be missing something, because the shift in proposals she's considering looks like a shift between exactly these two issues. By recognizing that it's a different view, she exhibits sensitivity to the distinction, so it's pretty strange to turn around in the next sentence and ignore it.

  3. How is she thinking about community knowledge versus individual knowledge? You're right, I think, that this is problematic if, in order for community C to know that p, it suffices that one of C's members knows that p. But you might impose more stringent requirements on community knowledge such that just because, say, one scientist knows that p, her community might not. (You might think that in order for C to know that p, it must be the consensus in C that p. Or that the evidence for p must be commonly available. And so on.) In that case, she might not be applying the anti-luminosity argument to a trivially luminous condition. Just a thought.