In Defining Reality, Edward Schiappa argues that definitional disputes should be treated less as philosophical questions of "is"and more as sociopolitical questions of "ought." Instead of asking "What is X?" he advocates that definitions be considered as proposals for shared knowledge and institutional norms, as in "What should count as X in context Y, given our needs and interests?"

Covering a broad scope of argument in rhetorical theory, as well as in legal, medical, scientific, and environmental debates, Schiappa shows the act of defining to be a specialized and learned behavior, and therefore one that can be studied and improved. In response to theories that deem discourse to be persuasive, the author asserts that all discourse is definitive discourse that contributes to our construction of a shared reality.

Defining Reality sheds light on our methods of creating common truths through language and argumentation and forces us to reconsider the contexts, limitations, and adaptability of our definitions. Hinging on a synthesis of arguments regarding the significance of definitional practices, the book is bolstered by a series of case studies of debates about rape, euthanasia, abortion, and political and environmental issues. These case studies ground Schiappa's concepts in reality and delineate the power of public discourse within legal contexts. Ranging widely among disciplines from philosophy and classical philology to constitutional law and cognitive psychology, this study substantially contributes to the scholarship of rhetoric and argumentation, particularly as they function in the realm of public discourse.