Duality vs Non-duality

Non-duality is not referred to the "variety" of reality (I see three different cars, a blue sky, a white cloud, the green grass and so on).

Non-duality is referred (I'm talking about "Advaita Vedanta" doctrine) to the dualism between "the seer and the seen."
Duality is if you percieve a separation between you and what you percieve. (the seer and the seen).
Non-duality is if you percieve a" whole" reality wthout any separation, no distinction between the seer and the seen.

It's impossible for those who has realized "the truth" to percieve the reality as duality.
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If for you, intimally, personally, you percieve a "dual reality" you have to go more deeper until you "find" the truth of non-duality (Advaita Vedanta)

(Monàs)