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. Synopsis While dreaming, one does not normally realize one is dreaming. On more rare occasions, the dream may be contained inside another dream with the very act of realizing that one is dreaming, itself, being only a dream that one is not aware of having. This has led philosophers to wonder whether it is possible for one ever to be certain, at any given point in time, that one is not in fact dreaming, or whether indeed it could be possible for one to remain in a perpetual dream state and never experience the reality of wakefulness at all. In Western philosophy this philosophical puzzle was referred to by Plato (Theaetetus 158b-d), Aristotle (Metaphysics 1011a6), and the Academic Skeptics. It is now best known from René Descartes' Meditations on First Philosophy. The dream argument has become one of the most prominent skeptical hypotheses. In Eastern philosophy this type of argument is sometimes referred to as the "Zhuangzi paradox": He who dreams of drinking wine may weep when morning comes; he who dreams of weeping may in the morning go off to hunt. While he is dreaming he does not know it is a dream, and in his dream he may even try to interpret a dream. Only after he wakes does he know it was a dream. And someday there will be a great awakening when we know that this is all a great dream. Yet the stupid believe they are awake, busily and brightly assuming they understand things, calling this man ruler, that one herdsman—how dense! Confucius and you are both dreaming! And when I say you are dreaming, I am dreaming, too. Words like these will be labeled the Supreme Swindle. Yet, after ten thousand generations, a great sage may appear who will know their meaning, and it will still be as though he appeared with astonishing speed. The Yogachara philosopher Vasubandhu (4th to 5th century C.E.) referenced the argument in his "Twenty verses on appearance only." The dream argument came to feature prominently in Mahayana and Tibetan Buddhist philosophy.