An illustration of the significance of forgetting is a paper by myself and David Laidler "What was lost with IS-LM" in the recent HOPE Supplement (vol 36, 2004) "The IS-LM Model: Its Rise, Fall, and Strange Persistence", edited by Michel De Vroey and Kevin D. Hoover. We argue there that the history of macroeconomics might have been very different had economists not forgotten about much that economists writing before 1936 understood well, rediscovering these ideas in an intellectual context that had changed dramatically. Of course, one has to be extremely careful with such counter-factual claims, which raise many difficult historiographic issues, but this example suggests the value of remembering the past, and hints at why it may sometimes be very difficult not to forget things. Roger Backhouse