On the physical level, we eventually come to realize that we are what we eat. What we put into our body becomes our body. On the mental level, we eventually discover that we are what we think. What we allow into our mind becomes our mind.
In the computer world a term was coined that describes perfectly this process: GIGO – garbage in, garbage out. GIGO means that when you enter garbage into a computer, you get garbage out of it again. The same principle operates inside each of us. If we feed our physical body with garbage – we can’t be surprised when our body turns to garbage. When we feed our minds with garbage, we should not be surprised at our thoughts also becoming junk.
What does it mean to think? We think we know, but do we? What is meant by mind? Again we think we know, but the closer we look, the less sure we become. The fact that we can even look for the mind makes us wonder – what is doing the looking? Can the mind find the mind? Can a fingertip touch itself? Can a subject be its own object?
These questions have been asked for thousands of years. The search for the mind, for our true nature, is ancient. It is useful to travel back to the beginning of some of these inquiries and understand the models that have been developed to help explain the mind and find our true nature. So let’s embark upon another side trip – a journey to discover the models of mind and true nature, as seen in the ancient and modern yogic teachings, the Buddhist teachings, and some of the modern Western psychological models.
We have already been introduced to one ancient model of the self via the five sheaths of the koshas. We have examined the physical and energy bodies. The remaining three sheaths are the lower mind, the higher mind, and the bliss body. The lower mind, called “manas,” is the home of our perceptions. The higher mind, called “vijnana,”  is the home of discrimination. Ananda, or bliss, which forms the final sheath, is the ultimate or next to ultimate Self, a source of underlying joy. 
As useful as the kosha model is to begin to see how the body is layered, it was never accepted by the yoga community: the model is not detailed enough. The yogis adopted a more complete model that seemed much more accurate and useful. Philosophers of the Samkhya tradition developed this model, and it seemed to fit with the yogi’s own experiences very closely. Let’s begin by investing the Samkhya view of the universe.