... we can claim to be able to know everything physical about what happens to a person when they taste something. We could observe all their bodily functions, specifically, the molecules of Marmite causing taste buds on the tongue to send messages to the brain via the nervous system, and certain fibres in the brain firing. We would be able to observe this with our own eyes and through the use of various medical apparatus, and would also be available for other people to observe and report the same observation. We may not know the true underlying nature of the observed, but would have knowledge of the sense data caused by these physical processes. However, surely this would not be knowledge of what Marmite actually tastes like. By observing the physical processes occurring in the body we may be aware of the various patterns of electrical current interacting in the nervous system ...

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