This book defines the concept and practices of literacy through a discussion of knowledge, information media, culture, subjectivity, science, communication, and politics. Examining the ways in which the spread of literacy and education have caused culture wars in pluralist societies since the 16^th century, the author reviews an interdisciplinary array of scholarly literature to contend that science, and more broadly evidence-based inductive arguments, offer the only reliable source information, and the only peaceful solution to cultural conflict in the 21^st century. With a focus on the multifaceted practice of literacy-as-communication as embedded within larger social and political processes, this book offers a comprehensive study of literacy through five core topics: knowledge, psychology, culture, science, and arguing over truth in pluralist democracies. The central thesis of the book argues that we require a new literacy that incorporates reading and writing with advanced cognitive and epistemological skills. Today’s citizens need to be able to understand the basic cognitive and cultural processes through which knowledge is created, and they need to know how to evaluate knowledge, peacefully debate knowledge, and productively use knowledge, for both personal decisions and public policy. How Do You Know? The Epistemological Foundations of 21^st Century Literacy is an interdisciplinary study that will appeal to scholars across the sciences and humanities, especially those concerned with pedagogy and the science of learning.