Why does adding cheese make a hamburger a "cheeseburger" whereas adding ketchup does not make it a "ketchupburger"? By the same token, how do we determine which things said at a meeting should be included in the minutes and which ought to be considered "off the record" and officially disregarded? Zerubavel illuminates the social foundation of mental actions such as perceiving, attending, classifying, remembering, assigning meaning, and reckoning the time. What takes place inside our heads, he reminds us, is deeply affected by our social environments, which are typically groups that are larger than the individual yet considerably smaller than the human race. Thus, we develop a nonuniversal software for thinking as Americans or Chinese, lawyers or teachers, Catholics or Jews, Baby Boomers or Gen-Xers. Zerubavel explores the fascinating ways in which thought communities carve up and classify reality, assign meanings, and perceive things, "defamiliarizing" in the process many taken-for-granted assumptions.