If I may butt in a bit...Does the Rational Mind exist? If so, is it the unified whole (it can't be part of it otherwise the unified whole wouldn't be a unified whole without parts)? Or, is it outside of, and separate from Reality? If that is the case, we would have to conclude that the Rational Mind is not real but nonetheless exists, wouldn't we?
"Rational Mind" is referring to "subjective experience", not to a physical "thing" having an experience.
Like Mosassam mentioned, it is hard to see all this because it is intrinsic to our mind (brain) that reality is classified into things.
It is not possible to understand or even to think about any system without breaking it into sensible "things" (that then can be thought of being in interaction with each others). Rational mind is based on this kind of classification process. (Another way to put it, the system is broken into semantical components, which make up the mental model we are aware of... Because of having a mental model of reality, we can make predictions about its behaviour. And all our rational behaviour is based on this capability of making predictions)
So, the subjective experience definitely exists, but if we want to understand the real nature of the subjective experience, it can be erroneous to assume identity to one's own mind. As if you are metaphysically the same person today that you were yesterday. What you have is memories of yesterday; existing by the virtue of physical configuration of the brain. What is there that persists in a person metaphysically? Well, there is absolutely no need to assume anything else persists from moment to moment, but the memories. It is part of our semantical worldview that we assume there is an objective "self"
This is not the most complicated philosophy but it is not the most intuitive one either... Still it comes as a kind of a natural revelation to many people at some point during their lives. At least to those who are inclined towards materialism.
For a deeper look, check out: