The Skills of Argument presents a comprehensive empirical study of informal reasoning as argument, involving subjects across the life span. Subjects ranging in age from adolescence to late adulthood were asked to describe their views on social problems that people have occasion to think and talk about in everyday life, such as crime and unemployment. In addition to providing supporting evidence for their theories, subjects were asked to contemplate alternative theories and counterarguments and to evaluate new evidence on the topics. This is the first major study of informal reasoning across the life span. Highlighting the importance of argumentive reasoning in everyday thought, the book offers a theoretical framework for conceptualizing and studying thinking as argument. The findings address issues of major importance to cognitive and developmental psychologists, as well as educators concerned with improving the quality of people’s thinking. The work is also relevant to philosophers, political scientists, and linguists interested in informal reasoning and argumentive discourse.