Marshall McLuhan's tetrad of media effects uses a tetrad - a four-part construct - to examine the effects on society of any technology/medium (that is, 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. The tetrad first appeared in print in articles by McLuhan in the journals Technology and Culture (1975) and et cetera (1977). It first appeared in book form in his posthumously-published works Laws of Media (1988) and The Global Village (1989).

The tetrad

The tetrad consists of four questions. 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 the media theory of Harold Innis 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, where the left/right direction reflects the figure/ground association. 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.

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