Marshall McLuhan once said that the last thing a fish would ever notice in it’s habitat is the water. Likewise, the most obvious and powerful realities of our human culture seem to also be the most unrecognised. http://stoweboyd.com/2013/07/12/marshall-mcluhan-once-said-t...
Like how we never notice air. Oh wait...
Plato describes it thus:
"There are similar differences in the air; of which the brightest part is called the aether, and the most turbid sort mist and darkness; and there are various other nameless kinds which arise from the inequality of the triangles."
http://classics.mit.edu/Plato/timaeus.html
Mist, darkness and aether are completely unrelated to any modern definition of air.