On page 167 of The Greening of America  Charles 
Reich notes that “the medium is the message 
means that there is no content in any medium.” 
This statement is actually one of the few useful 
remarks that has ever come to my attention 
about anything I have written. It enables me to 
see that the user of the electric light, or a 
hammer, or a language, or a book, is the content. 
As such, there is a total metamorphosis of the 
user by the interface. It is the metamorphosis 
that I consider the message.

Marshall McLuhan to Edward T. Hall, Jan. 21, 
1971, Letters of Marshall McLuhan , (Toronto,