 Hayek also maintained that requirements of clarity, prospectivity and so on make an important contribution to predictability, which he thought was indispensable for individual freedom. Predictability is often cited as a Rule-of-Law virtue. In his well-known recent book on the subject, Tom Bingham indicated that one of the most important things people needed from the law that governed them was predictability in the conduct of their lives and businesses. He quoted Lord Mansfield to the effect that 