  Although there are many general metaphysical/ontological theories of consciousness, the list of specific detailed theories about its nature is even longer and more diverse. No brief survey could be close to comprehensive, but seven main types of theories may help to indicate the basic range of options: higher-order theories, representational theories, interpretative narrative theories, cognitive theories, neural theories, quantum theories and nonphysical theories.  The categories are not mutually exclusive; for example, many cognitive theories also propose a neural substrate for the relevant cognitive processes.  Nonetheless grouping them in the seven classes provides a basic overview.