Todd Kappelman wrote: The tetrad allowed McLuhan to apply four laws, framed as questions, to a wide spectrum of mankind’s endeavors, and thereby give us a new tool for looking at our culture.
The first of these questions or laws is “What does it (the medium or technology) extend?” In the case of a car it would be the foot, in the case a phone it would be the voice. The second question is “What does it make obsolete?” Again, one might answer that the car makes walking obsolete, and the phone makes smoke signals and carrier pigeons unnecessary. The third question asks, “What is retrieved?” The sense of adventure or quest is retrieved with the car, and the sense of community returns with the spread of telephone service. One might consider the rise of the cross-country vacation that accompanied the spread of automobile ownership. The fourth question asks, “What does the technology reverse into if it is over-extended?” An over-extended automobile culture longs for the pedestrian lifestyle, and the over-extension of phone culture engenders a need for solitude.