Logic is of course a general resource for reasoning at large. But in the first half of the twentieth century, it developed particularity with a view to mathematical applications, and the field of mathematical logic came into being and flourished. In the second half of the century, much the same happened with regard to philosophical applications. Hence philosophical logic. The deliberations of this book cover a varied but interrelated array of key issues in the field. They address the representation of information in linguistic formulation, and modes of cogent demonstration in logic, mathematics, and empirical investigation, as well as the role of logic in philosophical deliberations. Overall, the book seeks to demonstrate and illustrate the utility of logic as a productive resource for rational inquiry at large.