The Upanishads are called shruti, revelations. Madnukya Upanishad, though the shortest of all Upanishads, is a most revered, profound Upanishad that teaches us how to know four states of consciousness: the waking, dreaming and sleeping states, and Turiya, the fourth state, beyond the first three. In this Upanishad, there is a unique combination of psychology and profound philosophy; a clear exposition and understanding of four states of consciousness.