Alétheia.

Greek word, Alétheia; ''A'' is a privative particle and Letheia, Letos, forgetfulness, from forgetfulness comes the river Letos which is the one to cross to reach Tartarus, what is truth? The unveiling. To remove the veil, the main veil is oblivion. Truth is memory. Truth is the reality of things. To distinguish the real from the fantasy you have to look at the details; in a dream we cannot know what the color of our socks is because there are no details, the details make the difference between the real and the fictitious.