Piero Scaruffi(Copyright © 2013 Piero Scaruffi | Legal restrictions )
These are excerpts and elaborations from my book "The Nature of Consciousness"
The Identity Theory
The main issue with any materialistic theory is how the mind (thoughts, feelings) can be explained from what we know of matter. If mind is ultimately matter, then what is it made of and how is it built? How, in other words, can the mental be reduced to the physical?
The "Identity theory" was first advanced by the British (albeit Australian residents) philosophers Ullin Place ("Is consciousness a brain process", 1956) and John Smart ("Sensations and brain processes", 1959). They claimed that perceptions and consciousness are physical processes in the brain, just like lightning is a physical process in the air. They went as far as identifying conscious states with brain states. This removes the question of where the mind-body interaction occurs: since conscious states and physical states are the same thing, they don't need to interact. They "behave" together. A desire, for example, is both a conscious and physical state that causes some actions that are both conscious and physical states.
As Herbert Feigl put it, mental states and physical states have the same “extension” but different “intension”: they describe the same states, but in a different way. Mental idioms and physical idioms are different descriptions of the same states. From the viewpoint of the man on the street, this thesis is difficult to defend, as mental and physical states are "obviously" different (pain, fear, love as opposed to electrochemical processes in the brain). An old philosophical trick, the so called "Leibniz's law", holds that two things are identical if and only if all the properties that apply to the first one also apply to the second, and viceversa. But the properties of mental states (such as emotions) and the properties of physical states (such as electrical and chemical properties) are obviously different.
There are several variants of the identity theory.
Instead of limiting the identity theory to consciousness and sensations, the US philosopher David Lewis ("An argument for the identity theory", 1966) and the Australian philosopher David Malet Armstrong extended it to everything that is mental, not just consciousness and perceptions: all mental states are physical states in the brain, all mental processes are brain processes. Furthermore, mental states have a "causal" role: a mental state (eg, a belief, a desire, a fear) may cause behavior, and it does so because it is a brain state. A mental state (which is a brain state) both is caused by and causes behavior. For example, lightning is not only a physical process in the air: it is caused by that physical process. A mental state is defined by its causal role: what causes the mental state, what behavior the mental state in turn causes, and its relationship with other mental states.
Whatever their spin on the identity theory, all these philosophers faced the same problem: how to explain the emotions we feel, which are obviously very different in nature from a piece of matter.
There are two main arguments against physicalism. The knowledge argument, by the Australian philosopher Frank Jackson ("Epiphenomenal Qualia" 1982) is about a scientist who has a complete understanding of the science of color, but has never experienced color: will she learn something new the first time that she experiences color? If yes, then it means that there cannot be a complete physical explanation of mental states.
The zombie argument was originally proposed by the US philosopher Saul Kripke ("Naming and Necessity", 1972) using the “philosophical zombie” thought experiment by the US philosopher Thomas Nagel ("Armstrong on the Mind", 1970). If a world in which all physical facts are the same as those of the real world must contain everything that exists in the real world, then a world of non-conscious (zombie) human beings physically identical to the real world of conscious human beings must contain consciousness.
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