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Multiple realizability
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Multiple realizability
In the philosophy of mind, multiple realizability is the thesis that the same mental property, state, or event can be implemented by different physical properties, states, or events.
Philosophers of mind have used multiple realizability to argue that mental states are not the same as—and cannot be reduced to—physical states. They have also used it to defend or criticize many versions of functionalism, especially machine-state functionalism.
The multiple realizability thesis in the philosophy of mind posits that the same mental state can be realized by different physical states; another way of putting it is that there is a many-to-one mapping from physical states to mental states. Multiple realizability in general is not restricted to the multiple realizability of mental states. Many kinds of things can be realized by numerous physical devices. A wide variety of physical devices can serve as corkscrews, for example. Mental states can also be realized in a variety of ways. Just as the logical states of a Turing machine can be realized by different structural states in different mechanisms, so, by analogy, the mental states of a human being can be realized by different physical states in different individuals. Pain, for example, is correlated with different physical states of the nervous system in different organisms, but the organisms all experience the mental state of "being in pain."
Mental states have been claimed to be multiply realizable not only across species and between individuals but also within individuals. At different times, the same individual may realize the same mental states in physically different forms. Neural plasticity—the fact that areas of the brain can assume the functions of other parts that have been damaged as the result of traumatic injury, pathology, natural biological development, or other processes—has long been considered to be an example. But so are more mundane facts about neurophysiology, such as the fact that neurons die and connections between them are rewired. The argument that neural plasticity supports multiple realizability has also been contested.
Gualtiero Piccinini differentiates three related properties: variable realizability, multiple realizability, and medium independence.
Multiple realizability has been used as an argument against type-identity theory, against reductionist theories of mind in general, for functionalist theories of mind, and even against functionalist theories of mind.
Starting in the 1960s, Hilary Putnam used multiple realizability as an argument against type-identity theory. Specifically, Putnam noted that the multiple realizability of pain entails that, contrary to type-identity theory, pain is not identical to C-fibre firing. More generally, multiple realizability shows that psychological attributes are not the same as physical attributes. Psychological attributes, rather, are disjunctions of physical attributes. Fodor, Putnam, and others noted that, along with being an effective argument against type-identity theories, multiple realizability implies that any low-level explanation of higher-level mental phenomena would be insufficiently abstract and general.
Jerry Fodor (1975) deployed multiple realizability more generally as an argument against any reductionist account of the relation between higher-level sciences and physics. Fodor also uses multiple realizability to argue against reductionism not only of psychology but of any special sciences (that is, any sciences that are "higher level" than physics). In his characterization of reductionism, all mental kind predicates in an ideal and completed psychology must correspond with physical kind predicates in an ideal and completed physics. He suggests taking Ernest Nagel's theory of reduction, which insists on the derivability of all terms in the theory to be reduced from terms in the reducing theory and the bridging laws, as the canonical theory of reduction. Given generalized multiple realizability, the physical science part of these psychophysical bridge laws will end up being a (possibly infinite) disjunction of all the terms referring to possible physical realizations of a mental kind. This disjunction cannot be a kind-predicate and therefore the entire statement cannot be a law of physics. The special sciences therefore cannot be reduced to physics.
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Multiple realizability AI simulator
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Multiple realizability
In the philosophy of mind, multiple realizability is the thesis that the same mental property, state, or event can be implemented by different physical properties, states, or events.
Philosophers of mind have used multiple realizability to argue that mental states are not the same as—and cannot be reduced to—physical states. They have also used it to defend or criticize many versions of functionalism, especially machine-state functionalism.
The multiple realizability thesis in the philosophy of mind posits that the same mental state can be realized by different physical states; another way of putting it is that there is a many-to-one mapping from physical states to mental states. Multiple realizability in general is not restricted to the multiple realizability of mental states. Many kinds of things can be realized by numerous physical devices. A wide variety of physical devices can serve as corkscrews, for example. Mental states can also be realized in a variety of ways. Just as the logical states of a Turing machine can be realized by different structural states in different mechanisms, so, by analogy, the mental states of a human being can be realized by different physical states in different individuals. Pain, for example, is correlated with different physical states of the nervous system in different organisms, but the organisms all experience the mental state of "being in pain."
Mental states have been claimed to be multiply realizable not only across species and between individuals but also within individuals. At different times, the same individual may realize the same mental states in physically different forms. Neural plasticity—the fact that areas of the brain can assume the functions of other parts that have been damaged as the result of traumatic injury, pathology, natural biological development, or other processes—has long been considered to be an example. But so are more mundane facts about neurophysiology, such as the fact that neurons die and connections between them are rewired. The argument that neural plasticity supports multiple realizability has also been contested.
Gualtiero Piccinini differentiates three related properties: variable realizability, multiple realizability, and medium independence.
Multiple realizability has been used as an argument against type-identity theory, against reductionist theories of mind in general, for functionalist theories of mind, and even against functionalist theories of mind.
Starting in the 1960s, Hilary Putnam used multiple realizability as an argument against type-identity theory. Specifically, Putnam noted that the multiple realizability of pain entails that, contrary to type-identity theory, pain is not identical to C-fibre firing. More generally, multiple realizability shows that psychological attributes are not the same as physical attributes. Psychological attributes, rather, are disjunctions of physical attributes. Fodor, Putnam, and others noted that, along with being an effective argument against type-identity theories, multiple realizability implies that any low-level explanation of higher-level mental phenomena would be insufficiently abstract and general.
Jerry Fodor (1975) deployed multiple realizability more generally as an argument against any reductionist account of the relation between higher-level sciences and physics. Fodor also uses multiple realizability to argue against reductionism not only of psychology but of any special sciences (that is, any sciences that are "higher level" than physics). In his characterization of reductionism, all mental kind predicates in an ideal and completed psychology must correspond with physical kind predicates in an ideal and completed physics. He suggests taking Ernest Nagel's theory of reduction, which insists on the derivability of all terms in the theory to be reduced from terms in the reducing theory and the bridging laws, as the canonical theory of reduction. Given generalized multiple realizability, the physical science part of these psychophysical bridge laws will end up being a (possibly infinite) disjunction of all the terms referring to possible physical realizations of a mental kind. This disjunction cannot be a kind-predicate and therefore the entire statement cannot be a law of physics. The special sciences therefore cannot be reduced to physics.