Sunday, June 21, 2009

Allegedly inconsistent knowledge principles

Matt Weiner argues that 'our use of the word "know" is best captured by' an inconsistent set of inference rules. His setup strikes me as strange. He writes:
These are the Knowledge Principles:
(Disquotational Principle)  An utterance of “S knows that p” at time t is true iff at time t S knows-tenseless that p.
(Practical Environment Principle)  S’s evidence concerning p is good enough for knowledge iff S’s evidence for p is good enough to make it epistemically rational for her to act on the assumption that p.
(Parity of Evidence Principle) If the evidence concerning p for S and T is the same, then S’s evidence is good enough for knowledge iff T’s evidence is good enough for knowledge.

The Knowledge Principles are inconsistent, given only the truism that different people can have different practical stakes. Take a Bank Case (DeRose 1992), in which Hanna and Leila each have the same rather good evidence that the bank is open Saturday, but acting on a mistaken belief would harm Hannah much more than Leila.  Hannah is in a high-stakes context, Leila in a low-stakes context.  The Practical Environment Principle, which entails that Leila knows that the bank is open and Hannah does not, here generates an inconsistency with the Parity of Evidence Principle, which entails that Leila knows if and only if Hannah does.

Two things strike me as really strange about this claim, even setting aside the question of whether these principles are plausibly constitutive of the meaning of 'knows'.

First, there are a lot of assumptions at play beyond "the truism that different people can have different practical stakes". The following are all tacit assumptions of Weiner's argument against the consistency of these the knowledge principles:

  • What it's epistemically rational (as opposed to prudentially, etc.) to do depends in constitutive part upon the practical stakes.

  • What evidence one has is invariant across practical stakes.

  • Leila's evidence is good enough for knowledge.


All of these, however, are controversial. Given the extremely radical claim that Weiner is trying to establish, these sorts of loose ends seem troublesome.

The second thing that strikes me as odd about this argument is that the Disquotational Principle seems to be doing no work at all.

1 comment:

  1. Hi Jonathan
    I have read the paper some time ago. Doesn't Weiner have some more cases? it seems your worries about this argument are well motivated.
    I thought the role of the Disquotation Principle was to rule out contextualism, which would be an obvious way to avoid inconsistency.

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