Over the course of history, different theories have been formulated to help explain the complex relationship between the mind and the body. One of the theories elucidating the mind-body relation is dualism—the view that mental states are independent from physical states. Mental states are ones of thinking, feeling, and believing whereas physical states are those outlined by physical and biological sciences. In contrast to dualism, physicalism insists that mental states are somehow physical states.
The most straightforward version of physicalism is the identity thesis—the theory that every type of mental state is identical to some type of physical state (Reasons and Responsibility, 285-286). Dualists and physicalists have disputed over the validity of the identity thesis; dualists denying its claim and physicalists defending it. The biggest problem facing physicalists and the identity thesis is the concept of qualia, the phenomenal quality of a mental state (Reasons and Responsibility, 281).
Philosopher Frank Jackson offers what he calls the “Knowledge Argument” for qualia. Jackson’s knowledge argument presents that nonphysical facts can be devised from facts about phenomenal quality. Through the concept of qualia, Jackson’s knowledge argument shows that the identity thesis is false. The identity thesis holds that mental events are simply identical with brain processes—identical in the same manner that sounds are identical with density waves in the air.
The thesis bases on the idea that mental states of thought, sensation, and awareness are alike those of physical states (such as those of the brain and central nervous system). An example of identity thesis is that lightning and an electric charge are two of the same thing. In other words, lightning is an electric charge. An advocate of the identity thesis is materialist Peter Carruthers. Carruthers argues that everything (including mental states) exists through physical causes.
Carruthers’ argument for the identity thesis can be summarized from the beliefs that some conscious states and events are casually necessary for the occurrence of some physical ones, and that there will be no need to advert to anything other than physical-physical causality in a completed neuro-physiological science. Thus, some conscious states and events are identical with physical brain states and events (Reason and Responsibility, 301-302). However, the concept of qualia refutes the idea of physicalism, and is the foundation of Jackson’s knowledge argument against identity thesis.
As a believer of dualism, Jackson uses the concept of qualia to support that the mind and matter are distinct and independent substances capable of existing without the other. Qualia are the subjective, felt qualities of experiences. For example, one may know all the physical properties of the color red and the physics behind why some things are red; however it is qualia that allows one to experience what it is like to actually see red. Jackson constructs his knowledge argument around the ideas of dualism and qualia.
To further illustrate Jackson’s argument for qualia (and dualism), the case of Fred and his unique color vision will be presented (Reasons and Responsibility, 298-299). For some reason, Fred has the ability to see two colors where others only see one. His retina is capable of distinguishing between two wavelengths of red in which others familiarizes with only one. He tries to explain the difference between the two reds. However he fails in doing so because others do not comprehend the difference.
Therefore it is concluded that Fred can visually see one more color than everyone else. Despite having all the physical information about Fred and his special trait, one cannot know what it actually feels like to see two different types of red. Thus, Jackson believes that the physicalist left something out in the theory of physicalism—the qualia or what it feels like to actually experience something. Consequently, quale explains how dualism is valid and physicalism is incomplete.
The existence of knowledge through qualia (mental state) and that of physical facts (physical state) demonstrates the idea of dualism—the view that two fundamental concepts exist. Jackson’s knowledge argument derives mainly from his thought experiment of Mary; the brilliant scientist who has spent her life confined within a black-and-white room and has never seen colors. Mary learns all the physical facts relevant to the mind. She becomes an expert on the neurophysiology of vision and knows all there is to know about color. When Mary is released from her room, she experiences color for the first time.
One would think intuitively that her color experiences provide her with knowledge she previously lacked, and that what she learns includes certain facts about what color experiences are like. The facts she learns upon her release cannot be physical facts because she already knew all physical facts before leaving the room. Therefore, the new knowledge comes from the concept of qualia, which indicates that not all facts are physical facts (Reason and Responsibility, 298-299). Thus physicalism is false. Jackson reaches his conclusion that the identity thesis is false by proving that mental states are not physical states.
According to the identity thesis, states and processes of the mind are identical to states and processes of the brain. The concept of qualia refutes the validity of the identity thesis by presenting subjective forms of experiences. The knowledge acquired from subjective forms of experiences differs from those of physical knowledge about experiences. Since physicalism requires that all aspects of knowledge are the same, physicalism cannot be sound. Thus the identity thesis must be false. The cases of Fred and Mary show that physicalism doesn’t amount to all knowledge.
The summation of Jackson’s knowledge argument can be illustrated by the following: before Mary leaves the room, she knows all the physical facts about color experiences. When Mary leaves the room, she learns new facts about color experiences—facts about what it’s like to see in color. Therefore, there are nonphysical facts about color experiences. Furthermore, the identity thesis is false because Jackson’s knowledge argument reveals that there is something about the experience of color (in Mary’s case) that cannot be captured by the physicalist view.
So, physicalism is incomplete. Physicalism lacks the phenomenal quality of the mental state—the ability to experience something regardless of physical knowledge. Qualia and the mental experience can never be achieved from the premises of physicalism and the identity thesis. Thus, the phenomenal quality of experiences cannot be accounted for through physical properties of the brain. In conclusion, the identity thesis is false because nonphysical properties, like phenomenal properties, exist.