The phrase was introduced in his most widely known book, Understanding Media: The Extensions of Man, published in 1964.^[1] McLuhan proposes that a medium itself, not the content it carries, should be the focus of study. He said that a medium affects the society in which it plays a role not only by the content delivered over the medium, but also by the characteristics of the medium itself.

McLuhan frequently punned on the word “message”, changing it to “mass age”, “mess age”, and “massage”; a later book, The Medium Is the Massage was originally to be titled The Medium is the Message, but McLuhan preferred the new title, which is said to have been a printing error.

For McLuhan, it was the medium itself that shaped and controlled “the scale and form of human association and action”.^[2] Taking the movie as an example, he argued that the way this medium played with conceptions of speed and time, transformed “the world of sequence and connections into the world of creative configuration and structure.”^[3] Therefore the message of the movie medium is this transition from “lineal connections” to “configurations”.^[4]

Extending the argument for understanding the medium as the message itself, he proposed that the “content of any medium is always another medium”^[5] – thus, the content of writing is speech, print is that of writing and print itself is the content of the telegraph.

McLuhan understood “medium” in a broad sense. He identified the light bulb as a clear demonstration of the concept of “the medium is the message”. A light bulb does not have content in the way that a newspaper has articles or a television has programs, yet it is a medium that has a social effect; that is, a light bulb enables people to create spaces during nighttime that would otherwise be enveloped by darkness. He describes the light bulb as a medium without any content. McLuhan states that “a light bulb creates an environment by its mere presence.”^[6]

Likewise, the message of a newscast about a heinous crime may be less about the individual news story itself — the content — and more about the change in public attitude towards crime that the newscast engenders by the fact that such crimes are in effect being brought into the home to watch over dinner.^[7]

Hence in Understanding Media, McLuhan describes the “content” of a medium as a juicy piece of meat carried by the burglar to distract the watchdog of the mind.^[8] This means that people tend to focus on the obvious, which is the content, to provide us valuable information, but in the process, we largely miss the structural changes in our affairs that are introduced subtly, or over long periods of time.^[7] As society’s values, norms and ways of doing things change because of the technology, it is then we realize the social implications of the medium. These range from cultural or religious issues and historical precedents, through interplay with existing conditions, to the secondary or tertiary effects in a cascade of interactions^[7] that we are not aware of.