 Functionalist theories in particular rely heavily on the notion of realization to explicate the relation between consciousness and the physical. According to functionalism, a state or process counts as being of a given mental or conscious type in virtue of the functional role it plays within a suitably organized system (Block 1980a). A given physical state realizes the relevant conscious mental type by playing the appropriate role within the larger physical system that contains it. (See the entry on   functionalism.)  The functionalist often appeals to analogies with other inter-level relations, as between the biological and biochemical or the chemical and the atomic. In each case properties or facts at one level are realized by complex interactions between items at an underlying level.