The difference between what is really present physically (physical or objective reality) and what we actually experience mentally (subjective or phenomenal reality) has been an issue at least since the early greeks. Some accept naive realism,saying that what we experience mentally is exactly the same as what is present physically. Many others,however,say that at least something is lost or gained in the translation from physical to phenomenal experience. A discrepancy between the two types of experience can exist if the sense receptors can respond only partially to what is physically present for example, to only certain sounds or colors. A discrepancy can also exist if in formation is lost or distorted as it is being transmitted from the sence receptors to the brain. Also, the brain itself can transform sensory information, thus creating a discrepancy between physical and phenomenal reality.The important question here is, Given the fact that there is a physical world and a psychological world, how are the two related? A related question is, Given the fact that all we can ever experience directly is our own subjective reality, how can we come to know anything about the physical world? We are confronted here with the problem of reification, or the tendency to believe that because something has a name it also has an independent existence.