Substrate indifference holds that intelligence depends on functional organization, not on whether a system is made of biological tissue or other materials. In Legg’s functionalist view, understanding matters only insofar as it changes measurable performance: if two systems behave identically across environments, this framework offers no practical basis for crediting one with more understanding. section 9.3.1
The lookup-table challenge
A huge lookup table can produce intelligent-looking responses to Chinese without anyone in the room understanding Chinese. Legg’s response is that any understanding that improves performance will show up in the system’s results across environments and tasks. The dispute turns on whether performance captures everything that matters about understanding. section 9.3.1
