McLuhan, Marshall (2014). «4: The Hot and Cool Interview». En Moos, Michel, ed. Media Research: Technology, Art and Communication: Critical Voices in Art, Theory and Culture. Critical Voices in Art, Theory and Culture. Routledge. p. 74. ISBN9781134393145. Consultado el 6 de mayo de 2015. «'System' means 'something to look at'. You must have a very high visual gradient to have systematization. In philosophy, before Descartes, there was no 'system.' Plato had no 'system.' Aristotle had no 'system.'».