Equivalent Worlds and Knowledge

One disturbing but telling demonstration of how definitions of knowledge can go wrong is due to Hawthorne.[1] Although properly intended as an attack on Dretske’s theory of conclusive reasons, it also works against Nozick’s conditional theory. Hawthorne provides a simple example: suppose, he declaims, that salmon induces hallucinations if eaten in great amounts. Suppose that, to be more precise, were you to eat it in amounts greater than 14 pounds at one go (never mind how that is humanly possible), it could cause you to believe that you’ve only had a few tidbits of the savoury fish. Then, on Dretske’s account, if P is the proposition I ate less than 1 pound of salmon, I could know P. On the other hand, let Q be the proposition I ate less than 14 pounds of salmon. Q is not knowable, because were Q to be false, I might still experience the hallucination that I’ve eaten less than a pound of salmon, and therefore I do not have conclusive reasons for Q