A medium communication is a system that enables the flow of messages between one or more creators of messages and one or more receivers of messages. The range of media therefore includes such simple systems as face to face communication, in which human modalities, light, and air are all that is necessary to enable communication and such complex media as television, in which a broad range of intermediate elements are used as a system to route messages from a small number of message creators to a large number of message consumers.
New communication media are invented in five interrelated "spheres" of invention as shown in the picture: mediators, characteristics, uses, effects, and practices. The “invention” of a medium entails invention activity in all of these spheres, with changes any one sphere provoking activity in others. The most common paths for such provocations are shown as the Cycle of Media and Cycle of Genre in the above picture.
Mediators are the fundamental building blocks of media, and include (using the telephone as an example) such things as telephones, telephone wires, telephone switches, operators, and billing systems. All media entail mediators. Even face-to-face communication depends on human modalities and the natural resources (air and light) that allow them to function. New media are built in the sphere of mediators, with resources (including technologies and people) organized (in structure and process) to support the creation and consumption of messages.