The idea that knowledge produces fact while imagination produces fiction is wrong, says a professor of logic at Oxford. Imagination is crucial to fundamental cognitive abilities. "Imagining turns out to be much more reality-directed than the stereotype implies," says professor Timothy Williamson. "Constraining imagination by knowledge does not make it redundant. We rarely know an explicit formula that tells us what to do in a complex situation. We have to work out what to do by thinking through the possibilities in ways that are simultaneously imaginative and realistic, and not less imaginative when more realistic. Knowledge, far from limiting imagination, enables it to serve its central function."