To understand Understanding Media, one should recognize the basic argument of the book: Media matters, but content does not. This discussion of information exchange is noticeably dual in nature: McLuhan believes that Media is essentially partially content and partially form, and that only the form itself carried meaning. In other words, the book is modernist in its approach.
In the 1960's, during the time of the book's population, modernism was rampant and effective. Still, Understanding Media was regarded as highly controversial because of its diagnosis of content. McLuhan said that even content is merely another medium's message in disguise. One might wonder if this idea is being influenced by the theory of relativity (matter is to energy what content is to form). McLuhan's preference of form over content is also like neo-Platonism, because Plato's philosophies prized metaphysical reality above the observable world.
Later these arguments would be challenged by post modernist thinkers who argued that even the effect of media itself would be a subjective experience, and that the only "meaning" one could derive from media was self-imposed. But for now, McLuhan wins the day, and his arguments are still formidable within their context.
