The central claim of this book is that when a court considers whether to develop or change a common law rule, the retroactive effect of doing so should explicitly be considered and, informed by the common law's approach to statutory construction, presumptively be resisted. As a platform for this claim, a definition of 'retroactivity' is established and a review of the history of retroactivity in the common law is provided. The argument is then that certainty - particularly in the form of an ability to rely on the law - and a conception of negative liberty constitute rationales for a general...