Marshall McCluhan begins his 1964 book Understanding Media: The Extensions of Man with the paradoxical statement that “the medium is the message.” He argues that the specific content being communicated is less important than the medium through which people communicate.
He cites as an example, a simple light bulb. The light bulb is a medium without a message, but is overlooked as a communication medium because it “has no ‘content.’” If many light bulbs spell out a word, the word is the ‘content’ and becomes the focus of our attention. The light bulbs are the medium, even though the light bulbs haven’t changed.
This still seems paradoxical and unsatisfying. It is helpful to consider what he means when he uses the term “medium” and “message.”
He defines a “message” as “the change of scale or pace or pattern that it introduces into human affairs”. The message isn’t a set of facts or banal statements, it is an impact on human behavior and interaction.
He defines a “medium” as “any extension of ourselves.” The medium isn’t a specific technology like a telephone or a radio, it is how the technology affects society.
So when he claims that the “medium is the message,” he is saying that a communication technology’s impact on society dominates human interaction. The specific content being communicated is secondary. He wrote this in response to what he saw as an overemphasis on the analysis of content without considering how the content being communicated was affecting society.
Still somewhat paradoxical, but perhaps this was McCluhan’s intent when coining this phrase. By attempting to analyze this we turn our focus to the specific ways we project our thoughts and ideas into the world. These mediums are what influence human behavior, not the thoughts and ideas themselves.