The Tatwa Bodha by Sri Adi Sankaracharya lists all that which is not me. It gives a detailed analysis of the body—gross, subtle and causal. Then the master says that just as the objects that I can see are not me, in the same way the body, mind and the qualities deep down are not me.
If all that I see is not me, then who am I? The frustrated student is bound to ask. The teacher comes to the point: You are of the essential nature of Satchitananda. Sat means that which exists in all three periods of time. There is only one thing that exists as life and there is nothing other than this. If that existence manifests, we say the person is alive. If it becomes unmanifest, then we say the person is dead. Existence has always been in the past. Existence alone stays in the present and existence will continue to in the future too.
Chit is a word that comes from Chaitanya. It means power, force, consciousness, the ability to know and throw the light of knowledge on inert objects too. Outside the body, Chaitanya can be understood as the enlivening life principle in all living things. In inert objects, the principle of existence is known as is—the laptop is, the mobile phone is, the food plate is, the movie is.
Within the body, Chit is known by ourselves. We are aware that we are. In a dark room, I may need a torch to show where objects are. If someone calls out my name, I do not need a torchlight to know where I am. I know it without any aid. That knowledge of the self is called Chit. I know that I am.
While in common knowledge of things, beings and situations of the world, there is a tremendous variety to be known. Sky, earth, water, fire, air, sounds, forms, tastes, smells or different feelings and thoughts. All objects of knowledge are extremely unique and different. However, the one who knows is addressed as I am and that is the same through all the objects.
What is the nature of the third part of my personality—Ananda? It is of the nature of happiness. When happiness is experienced, followed by sorrow, followed by a little irritation, then by some anger and then a little happiness and then jealousy owing to comparison—happiness is not a complete experience. It is broken.
However, knowing that I am the one who experiences the joy, experiences the sorrow, experiences the irritation, experiences the anxiety, experiences the suffering or experiences anything for that matter—that experiencer is me and is always of the nature of joy and bliss. When I refer to myself as I, called atma in Sanskrit, it means I am this existence, consciousness and bliss and nothing else.