Generally speaking, a tetrad

Tetrad

Tetrad may refer to:* Tetrad , Bivalents or Tetrad of homologous chromosomes consisting of four synapsed chromatids that become visible during the Pachytene stage of meiotic prophase...

 is any set of four things. In Laws of Media (1988) and The Global Village (1989), published posthumously, Marshall McLuhan

Marshall McLuhan

Herbert Marshall McLuhan, CC was a Canadian educator, philosopher, and scholar—a professor of English literature, a literary critic, a rhetorician, and a communication theorist...

 summarized his ideas about media

Media studies

Media studies is an academic discipline and field of study that deals with the content, history and effects of various media; in particular, the 'mass media'. Media studies may draw on traditions from both the social sciences and the humanities, but mostly from its core disciplines of mass...

 in a concise tetrad of media effects. The tetrad is a means of examining the effects on society of any technology/medium (put another way: a means of explaining the social processes underlying the adoption of a technology/medium) by dividing its effects into four categories and displaying them simultaneously. McLuhan designed the tetrad as a pedagogical tool, phrasing his laws as questions with which to consider any medium:

1. What does the medium enhance?
2. What does the medium make obsolete?
3. What does the medium retrieve that had been obsolesced earlier?
4. What does the medium flip into when pushed to extremes?

The laws of the tetrad exist simultaneously, not successively or chronologically, and allow the questioner to explore the "grammar and syntax" of the "language" of media. McLuhan departs from his mentor Harold Innis

Harold Innis

Harold Adams Innis was a Canadian professor of political economy at the University of Toronto and the author of seminal works on media, communication theory and Canadian economic history. The affiliated Innis College at the University of Toronto is named for him...

 in suggesting that a medium "overheats", or reverses into an opposing form, when taken to its extreme.

Visually, a tetrad can be depicted as four diamonds forming an X, with the name of a medium in the center. The two diamonds on the left of a tetrad are the Enhancement and Retrieval qualities of the medium, both Figure qualities. The two diamonds on the right of a tetrad are the Obsolescence and Reversal qualities, both Ground qualities.

• Enhancement (figure): What the medium amplifies or intensifies. For example, radio amplifies news and music via sound.
• Obsolescence (ground): What the medium drives out of prominence. Radio reduces the importance of print and the visual.
• Retrieval (figure): What the medium recovers which was previously lost. Radio returns the spoken word to the forefront.
• Reversal (ground): What the medium does when pushed to its limits. Acoustic radio flips into audio-visual TV.

See also

• Hot and cool media
• Time- and space-bias
• Figure and ground
  Figure and ground (media)
  Figure and ground is a concept drawn from Gestalt psychology by media theorist Marshall McLuhan, which in his work underpins the meaning of his famous phrase, "The medium is the message." He used this concept to explain how a communications technology, the medium or figure, necessarily operates...