Online Papers - Brian Weatherson

Knowledge, Bets and Interests 132
p ¬ p
Do ϕ -5 -5
Do ψ -5 -5
Find out which is harmful -1 -1
In fact, the doctor is making a decision under certainty. She knows that the value of
prescribing either medicine is -5, and the value of running the tests is -1, so she should
run the tests.
In general, when an agent has a duty to maximise the expected value of some
quantity Q, then the value that goes into the agent’s decision table in a cell is not the
value of Q in the world-action pair the agent represents. Rather, it’s the expected
value of Q given that world-action pair. In situations like this one where the relevant
facts (e.g., which medicine the patient is allergic to) don’t affect the evidence the agent
has, the decision is a decision under certainty. This is all as things should be. When
you have obligations that are drawn in terms of the expected value of a variable, the
actual values of that variable cease to be directly relevant to the decision problem.
One upshot of these considerations is that when moral and epistemic considerations
get entangled, for example when agents have a moral duty not to take certain
kinds of risks, it can get tricky to apply the theory of belief developed here. In a
separate paper (“Defending Interest-Relative Invariantism”) I’ve shown how this idea
can help respond to some criticisms of similar views raised by Jessica Brown (2008).
3 Fantl and McGrath on Interest-Relativity
Jeremy Fantl and Matthew McGrath (2009) have argued that my interest-relative theory
of belief cannot explain all of the interest-relativity in epistemology. I’m going
to agree with their conclusion, but not with their premises. At this point you might
suspect, dear reader, that you’re about to be drawn into a micro-battle between two
similar but not quite identical explanations of the same (alleged) phenomena. And
you wouldn’t be entirely mistaken. But I think seeing why Fantl and McGrath’s objections
to my theory fail will show us something interesting about the relationship
between interests and knowledge. In particular, it will show us that interests can
generate certain kinds of defeaters of claims to knowledge.
Fantl and McGrath’s primary complaint against the interest-relative theory of
belief I developed in my Weatherson (2005a) and in the previous section is that it is
not strong enough to entail principles such as (JJ).
(JJ) If you are justified in believing that p, then p is warranted enough to justify you
in ϕ-ing, for any ϕ. (Fantl and McGrath, 2009, 99)
In practice, what this means is that there can’t be a salient p,ϕ such that:
• The agent is justified in believing p;
• The agent is not warranted in doing ϕ; but
• If the agent had more evidence for p, and nothing else, the agent would be be
warranted in doing ϕ.