This paper critically examines Timothy Williamson’s claim that knowledge figures essentially in explanations of behavior. Since this claim implies that knowledge is causally efficacious in bringing about actions, it plays a key role in Williamson’s case for knowledge being a mental state. I first discuss a central example of Williamson, in which a burglar ransacks a house. I dispute Williamson’s claim that the best explanation of the burglar’s behavior invokes the burglar’s state of knowledge as he enters the house, by (...) arguing that there is a better explanation that only mentions the burglar’s beliefs. Since the reasons that explain the superiority of my proposed explanation generalize, I conclude that one does not have to invoke a subject’s state of knowledge to explain behavior. Nevertheless, Williamson’s explanation is superior to belief-based explanations if one only considers facts that obtain before the action takes place. In the final part of the paper, I argue that this fact does not help Williamson’s case for considering knowledge as a mental state. (shrink)