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