Daniel Kahneman was awarded the 2002 Nobel Memorial Prize in Economics "for having integrated insights from psychological research into economic science, especially concerning human judgment and decision-making under uncertainty." He is one of only two non-economists to be so honored. Some credit his work, alongside the late Amos Tversky , with laying the groundwork for the now-hot field of behavioral economics. Kahnneman spoke last month about that field, and about how rationally we all really behave when it comes to finance and economics, at Georgetown University's commencement. And he says the very definition of "rationality" in economics is different than it is in everyday language: