1993
The Metaphysics of Virtual Reality
Michael R. Heim

"When we look to the pioneers, we see virtual reality going off in several directions. The pioneers present us with at least seven divergent concepts currently guiding VR research. The different views have built camps that fervently disagree as to what constitutes virtual reality".

Michael Heim. The Metaphysics of Virtual Reality (New York: Oxford University Press, 1993).