The Self is the source of intelligence and wisdom in the body and mind. It is like God, a blissful, luminous, formless, unchanging and immortal principle, beginning less and endless. It is all pervading, self-illumined pure consciousness. Atman is beyond all phenomena in existence, beyond time, space and causation and it cannot be experienced or known by the senses or the mind or even the intellect. The Atman is known only through the developed intuition. The intuition is the all-knowing faculty of the Atman through which the Atman is known. The Atman, is the observer and experiencer of all changing phenomenon within the body and outside of it. Thoughts, emotions, desires, moods, arise and go away, replaced by others which also passes away. The witness the Atman who watches all inner and outer changes remains unchanged and untouched. 

The Atman exists equally in all beings, animate as well as inanimate, in rocks and stones and trees as well as birds and beasts and men. At the heart of all whatever there is in the universe abides the Atman. Beings differ enormously in the degree, to which the Atman present has been realized. At the bottom of a vast scale are inanimate objects, somewhere in the middle is man and at the top are superhuman or higher astral or causal beings. When Atman forgets its divine nature and identifies itself with its instruments, the bodies and feels confined and limited it is then known as Jivatman or Jiva. The Jiva is enclosed in five bodies in the material universe. It has to come out of all the five bodies to attain liberation. 

States of consciousness  

The Jiva experiences three states of consciousness. 

The Waking  

When the Jiva is identified with the physical body and is functioning through the physical senses, it is in the waking state of consciousness. 

The Dreaming 

When consciousness withdraws from the physical body and becomes aware of the astral body and functions through the astral senses, that state is called the dreaming state. This state is reached every day when we sleep and dream. Yogis reach this state consciously through meditation and samadhi. 

The Deep Sleep  

When consciousness withdraws even from the astral body and becomes aware of the causal body and functions from there, then that state is called deep sleep state. All of us enter this state in moments of dreamless deep sleep. Advance yogis reach this state through deep meditation and samadhi. In sleep when we reach this state we wake up refreshed and relaxed. In samadhi when we reach the dream and the deep sleep states we come back to waking state with a sense of profound peace, bliss and higher wisdom. 

Turiya  

This us the fourth state or the transcendental state of consciousness. This cannot be reached through sleep. It is reached only through the highest Nirvikalpa Samadhi. When in deepest samadhi the consciousness withdraws even from the causal body and merges with the ocean of consciousness then that state is called Turiya or cosmic consciousness.