In philosophy, rationality is the exercise of reason.^{[citation needed]} It is the manner in which people derive conclusions when considering things deliberately. It refers to the conformity of one's beliefs with one's reasons to believe, or with one's actions with one's reasons for action. However, the term "rationality" tends to be used differently in different disciplines, including specialized discussions of economics, sociology, psychology and political science. A rational decision is one that is not just reasoned, but is also optimal for achieving a goal or solving a problem.

Determining optimality for rational behavior requires a quantifiable formulation of the problem, and the making of several key assumptions. When the goal or problem involves making a decision, rationality factors in how much information is available (e.g. complete or incomplete knowledge). Collectively, the formulation and background assumptions are the model within which rationality applies. Illustrating the relativity of rationality: if one accepts a model in which benefiting oneself is optimal, then rationality is equated with behavior that is self-interested to the point of being selfish; whereas if one accepts a model in which benefiting the group is optimal, then purely selfish behavior is deemed irrational. It is thus meaningless to assert rationality without also specifying the background model assumptions describing how the problem is framed and formulated.

Gerd Gigerenzer (born September 3, 1947, Wallersdorf) is a German psychologist who has studied the use of bounded rationality and heuristics in decision making, especially in medicine. A critic of the work of Daniel Kahneman and Amos Tversky, he argues that heuristics should not lead us to conceive of human thinking as riddled with irrational cognitive biases, but rather to conceive rationality as an adaptive tool that is not identical to the rules of formal logic or the probability calculus.

With Daniel Goldstein he first theorized the recognition heuristic.

He has written several books on the subject of heuristics and decision making, including Simple Heuristics That Make Us Smart (1999), and Bounded Rationality: The Adaptive Toolbox (2001) with Reinhard Selten. His two books for a lay audience, Reckoning with Risk: Learning to Live with Uncertainty (2002, published in the U.S. as Calculated Risks: How to Know When Numbers Deceive You), and Gut Feelings: The Intelligence of the Unconscious (2007), have been translated into 18 languages. "Rationality for Mortals", his most recent book, investigates decisions under limited time and information. He has trained U.S. Federal Judges, German physicians, and top managers in decision making and understanding risks and uncertainties.

Dan Ariely (born April 29, 1968) is an Israeli American professor of psychology and behavioral economics. He teaches at Duke University and is the founder of The Center for Advanced Hindsight.Ariely's talks on TED have been watched 2.8 million times. He is the author of Predictably Irrational and The Upside of Irrationality, both of which became New York Times best sellers.

Dan Ariely was born in New York while his father was studying for an MBA degree at Columbia University. The family returned to Israel when he was three. He grew up in Ramat Hasharon. In his senior year of high school, he was active in Hanoar Haoved Vehalomed, an Israeli youth movement. While preparing a ktovet esh (fire inscription) for a traditional nighttime ceremony, the flammable materials he was mixing exploded, causing third-degree burns over 70 percent of his body.

Ariely was a physics and mathematics major at Tel Aviv University, but transferred to philosophy and psychology when he found the writing too physically taxing. However, in his last year he dropped philosophy and concentrated solely on psychology, in which he received his B.A. He also holds an M.A. and Ph.D. in cognitive psychology from the University of North Carolina at Chapel Hill. He did a second doctorate in business administration at Duke University at the urging of Nobel economic sciences laureate Daniel Kahneman.

Andrew W. Lo is the Charles E. and Susan T. Harris Professor of Finance at the MIT Sloan School of Management. He is a leading authority on hedge funds and financial engineering; he proposed the Adaptive market hypothesis. He is the author of several academic articles in Finance and Financial economics.

He is the director of MIT's Laboratory for Financial Engineering, a research associate of the National Bureau of Economic Research, a member of the NASD's Economic Advisory Board, and founder and chief scientific officer of AlphaSimplex Group, LLC, a quantitative investment management company based in Cambridge, Massachusetts. AlphaSimplex specializes in quantitative global macro and global tactical asset allocation strategies, beta-replication products, and absolute-return risk analytics. He is an associate editor of the Financial Analysts Journal, the Journal of Portfolio Management, the Journal of Computational Finance, and Statistica Sinica. He is a former governor of the Boston Stock Exchange. He previously taught at the University of Pennsylvania's Wharton School. He testified in front of the Committee on Oversight and Government Reform of the U.S. House of Representatives.

Smile Empty Soul is an American post-grunge band from Santa Clarita, California.

Smile Empty Soul formed in 1998, while its original members were attending different high schools in the Santa Clarita area. The band, originally a three-piece group, consisted of vocalist and guitarist Sean Danielsen, bassist Ryan Martin and drummer Derek Gledhill.

After playing numerous hometown gigs, Smile Empty Soul ventured to the Castro District, and later passed a demo to John Parker of the West Hollywood indie label, ThroBack Records. That later led to a record deal with Jason Flom's Lava Records.

On May 27, 2003, the band released their self titled debut album Smile Empty Soul. The album was produced by John Lewis Parker, and three successful singles were released. In March 2005, the album was certified gold with sales in excess of 500,000+.

Sometime after the recording of their second album "Anxiety" was finished, drummer Derek Gledhill was replaced by Dominic Weir.

On September 22, 2005, during a concert at The Beaumont Club in Kansas City, Missouri, frontman Sean Danielsen stated that their new album Anxiety, would not be released due to issues with Lava Records. The band told fans that in order to receive the new album they could purchase one of a very limited number of burned copies or attempt to download the album online via BitTorrent.