Are all the facts about nations, cultures and economies really just facts about people's mental states and their interactions? Are all of the properties which determine whether or not a thing is a work of art really just physical properties of that thing? Is linguistics, the scientific investigation of language, best understood as a branch of psychology, the scientific investigation of the mind? Can psychology be reduced to biology? Can all biological phenomena be explained chemically? Is chemistry really just part of physics? Is there anything going on in the world which isn't a physical thing? Can there be freely-chosen, autonomous human action in a purely physical world? Frank Jackson has made a controversial claim about the way in which one should investigate questions like these. This paper is a qualified defence of that claim.