Philosophy is a discipline that makes no observations, conducts no experiments, and needs no input from experience. It is an armchair subject, requiring only thought. Yet that thought can advance knowledge in unexpected directions, not only through the discovery of new facts but also through the enhancement of what we already know. Philosophy can clarify our vision of the world and provide exciting ways to interpret it. Of course, philosophy's unified purpose hasn't kept the discipline from splintering into warring camps. Departments all over the world are divided among analytica.