Dream logic

“Whenever in my dreams I see the dead, they always appear silent, bothered, strangely depressed, quite unlike their dear, bright selves. I am aware of them, without any astonishment, in surroundings they never visited during their earthly existence, in the house of some friend of mine they never knew. They sit apart, frowning at the floor, as if death were a dark taint, a shameful family secret. It is certainly not then - not in dreams - but when one is wide awake, at moments of robust joy and achievement, on the highest terrace of consciousness, that mortality has a chance to peer beyond its own limits, from the mast, from the past and its castle tower. And although nothing much can be seen through the mist, there is somehow the blissful feeling that one is looking in the right direction.”

Nobokov ; Speak Memory

The dream argument is the postulation that the act of dreaming provides preliminary evidence that the senses we trust to distinguish reality from illusion should not be fully trusted, and therefore any state that is dependent on our senses should at the very least be carefully examined and rigorously tested to determine whether it is in fact "reality".

The dream argument . com