Unlike the natural sciences, in which observation and experimentation provide definitive evidence and lead directly to progress, the study of politics and world affairs rarely involves the resolution of debates—or even the accumulation of knowledge. This book represents an all-too-infrequent effort by a scholar of international relations to reflect on what political scientists do as a social scientific enterprise. Chernoff examines three core debates in the field of security studies: What are the causes of nuclear proliferation? What are the sources of alliance formation? And why do democracies tend to remain at peace with one another? Chernoff discovers that even in the relatively small and tightly integrated field of security studies, scholars have widely different views about what constitutes evidence and how to draw conclusions. Of course, drawing inferences about cause and effect in social and political interactions is notoriously difficult. But Chernoff is right to point out that the field of security studies must raise the bar when it comes to standards of evidence and measures of theoretical soundness.