Introduction: Book review by Andrew Louth is professor emeritus of patristic and Byzantine studies at the University of Durham; IAIN MCGILCHRIST’S The Matter with Things is a sequel to his previous volume The Master and His Emissary: The Divided Brain and the Making of the Western World (2009), in which he argued powerfully for the crucial importance of the notion that human beings, along with virtually all sentient creatures, have a brain split into two hemispheres, physically linked by a narrow corridor, the corpus callosum, across which there is only limited contact. That had been known since the middle of the 19th century, but only recently has it become clear that the two hemispheres have different characteristics.