Multiple Realizability
The multiple realizability thesis says that there is more than one way to create a specific mental experience. An alternative way to state this is to say that widely different physical systems can have the same mental experience. The implied consequence is that it is the function of the physical system that is causal to the mental experience, an idea I will refer to as functionalism. Historically, the concept of multiple realizability facilitated the move from identity theory to functionalism. Functionalism is more abstract than the identity theory and can therefore accommodate different physical entities causing the same mental experience.
Examples used to illustrate the claims made by the multiple realizability thesis differ in the level at which the systems differ. At the most fine grained level one may argue that replacing all the Carbon atoms with Silicone atoms in your brain will not alter the function of your brain and, consequently, your mental experiences with a Silicone brain would be the same as with your current Carbon brain. At a higher organizational level, each neuron could be replaced by an electrical device that performs the same function the neuron performs. These electrical devices would be connected to each other in the same way your neurons are currently connected to each other and therefore perform the same function - including producing a mental world. It is only one step further to replace the electrical devices with other components (for example citizens of China) that perform the same function. This system would, according to the multiple realizability thesis, still have - as a whole - a mental experience identical to the one you have. In these examples the neural architecture - the connections between and functions of the components that are neurons in your brain - remains unaltered. Each individual neuron in the brain is replaced by a silicon-neuron, an electrical device, or a citizen of China. The replacement for the neuron is
Examples used to illustrate the claims made by the multiple realizability thesis differ in the level at which the systems differ. At the most fine grained level one may argue that replacing all the Carbon atoms with Silicone atoms in your brain will not alter the function of your brain and, consequently, your mental experiences with a Silicone brain would be the same as with your current Carbon brain. At a higher organizational level, each neuron could be replaced by an electrical device that performs the same function the neuron performs. These electrical devices would be connected to each other in the same way your neurons are currently connected to each other and therefore perform the same function - including producing a mental world. It is only one step further to replace the electrical devices with other components (for example citizens of China) that perform the same function. This system would, according to the multiple realizability thesis, still have - as a whole - a mental experience identical to the one you have. In these examples the neural architecture - the connections between and functions of the components that are neurons in your brain - remains unaltered. Each individual neuron in the brain is replaced by a silicon-neuron, an electrical device, or a citizen of China. The replacement for the neuron is
Bibliography: Putnam, Hilary. "Psychological Predicates." In W.H. Capitan and D.D. Merrill (eds.), Art, Mind, and Religion. Pittsburgh: University of Pittsburgh Press (1967): 37-48. Putnam introduces the concept of multiple realizability Block, Ned and Fodor, Jerry. "What Psychological States Are Not." Philosophical Review 81 (1972): 159-181. Block, Ned. "Troubles With Functionalism." In. C.W. Savage (ed.), Perception and Cognition: Issues in the Foundations of Psychology. Minnesota Studies in the Philosophy of Science, vol. 9. Minneapolis: University of Minnesota Press (1978): 261-325. Bechtel, William and Mundale, Jennifer. "Multiple Realizability Revisited: Linking Cognitive and Neural States." Philosophy of Science 66 (1999): 175-207. Harnad, Stevan. "Can a Machine Be Conscious? How?" Journal of Consciousness Studies 10 (2003). Shapiro, Lawrence. "Multiple Realizations." Journal of Philosophy 97 (2000): 635-654.