UC San Diego

According to many philosophers, psychological explanation can legitimately be given in terms of belief and desire, but not in terms of knowledge. To explain why someone does what they do (so the common wisdom holds) you can appeal to what they think or what they want, but not what they know. Timothy Williamson has recently argued against this view. Knowledge, Williamson insists, plays an essential role in ordinary psychological explanation. Williamson's argument works on two fronts. First, he argues against the claim that, unlike knowledge, belief is "composite" (representable as a conjunction of a narrow and a broad condition). Belief's failure to be composite, Williamson thinks, undermines the usual motivations for psychological explanation in terms of belief rather than knowledge. Unfortunately, we claim, the motivations Williamson argues against do not depend on the claim that belief is composite, so what he says leaves the case for a psychology of belief unscathed. Second, Williamson argues that knowledge can sometimes provide a better explanation of action than belief can. We argue that, in the cases considered, explanations that cite beliefs (but not knowledge) are no less successful than explanations that cite knowledge. Thus, we conclude that Williamson's arguments fail both coming and going: they fail to undermine a psychology of belief, and they fail to motivate a psychology of knowledge.