MORPHEUS:
Have you ever had a dream, Neo, that you were so sure was real?

MORPHEUS:
What if you were unable to wake from that dream, Neo? How would you know the difference between the dreamworld and the real world?

Neo has woken up from a hell of a dream — the dream that was his life. How was he to know? The cliché is that if you are dreaming and you pinch yourself, you will wake up. Unfortunately, things aren't quite that simple. It is the nature of most dreams that we take them for reality — while dreaming we are unaware that we are in fact in a dreamworld. Of course, we eventually wake up, and when we do we realize that our experience was all in our mind. Neo's predicament makes one wonder, though: how can any of us be sure that we have ever genuinely woken up? Perhaps, like Neo prior to his downing the red pill, our dreams thus far have in fact been dreams within a dream.

The idea that what we take to be the real world could all be just a dream is familiar to many students of philosophy, poetry, and literature. Most of us, at one time or another, have been struck with the thought that we might mistake a dream for reality, or reality for a dream. Arguably the most famous exponent of this worry in the Western philosophical tradition is the seventeenth-century French philosopher Rene Descartes. In an attempt to provide a firm foundation for knowledge, he began his Meditations by clearing the philosophical ground through doubting all that could be doubted. This was done, in part, in order to determine if anything that could count as certain knowledge could survive such rigorous and systematic skepticism. Descartes takes the first step towards this goal by raising (through his fictional narrator) the possibility that we might be dreaming:

"How often, asleep at night, am I convinced of just such familiar events — that I am here in my dressing gown, sitting by the fire —when in fact I am lying undressed in bed! Yet at the moment my eyes are certainly wide awake when I look at this piece of paper; I shake my head and it is not asleep; as I stretch out and feel my hand I do so deliberately, and I know what I am doing. All this would not happen with such distinctness to someone asleep. Indeed! As if I did not remember other occasions when I have been tricked by exactly similar thoughts while asleep! As I think about this more carefully, I see plainly that there are never any sure signs by means of which being awake can be distinguished from being asleep. The result is that I begin to feel dazed, and this very feeling only reinforces the notion that I may be asleep." (Meditations, 13)
 

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