This comes up from time to time e.g. http://d-squareddigest.blogspot.com/2007/05/bits-and-pieces-congestion-pricing-road.html and nobody has a cite. There's a certain kind of fame that leads people people to invent attributions e.g. countless saccharine banalities credited to Albert Einstein. Here's a more general history-of-economic-thought question. Would Keynes have used "irrational" in this way? Colin Danby