We have to admit that perception ... cannot be explained mechanically… If we imagine a machine whose construction ensures that it has thoughts, feelings, and perceptions, we can conceive it to be so enlarged, while keeping the same proportions, that we could enter it like a mill. On that supposition, when visiting it we shall find inside only components pushing one another, and never anything that could explain a perception. — Leibniz (1646–1716), Monadologie, §17.
Functionalists would reply that you need to know what functions are involved in having ‘thoughts, feelings and perceptions’. Looking at the machinery won’t tell you.
Epiphenomenalism. Developments in the 19th century encouraged the idea that physics could explain all explicable physical events: that the physical world is ‘closed under causation’. But what about consciousness? Experiences seem unlike anything physical. Epiphenomenalists concluded that consciousness was non-physical and has no effects on the physical world: we are ‘conscious automata'.
Zombies. Which suggests a strange possibility: creatures exactly like us in all physical details and behaving exactly like us, yet not conscious – ‘philosophical’ (not folkloric) zombies. Of course natural laws rule that out. But if it were only 'logically' possible, physicalism would be false. However, there are strong reasons to think it is not possible, mainly to do with the causal links between consciousness and behaviour.
"Nobody has the slightest idea how anything material could be conscious. Nobody even knows what it would be like to have the slightest idea about how anything material could be conscious. So much for the philosophy of consciousness." – J A Fodor, ‘The Big Idea: Can there be a Science of Mind?’, Times Literary Supplement, 3 July 1992.
In ‘What is it Like to Be a Bat?’ Thomas Nagel maintains that the ‘subjective character of experience…is not analysable in terms of any explanatory system of functional states…’. We can’t tell what it is like to be such an alien creature as a bat. He thinks such knowledge lies beyond the grasp of physicalism and functionalism. But we need to distinguish between knowing what it is for there to be something it is like, and knowing what experiences are like.
Jackson’s Mary. Mary is a super-scientist who has normal vision but has been kept in a colourless environment from birth. She knows all the physical facts about colour vision, but when she emerges from her grey world and sees colours for the first time, it seems she immediately acquires new information: she learns what it is like to see the blue sky, red tomatoes, and so. In ‘Epiphenomenal Qualia’ Frank Jackson concludes that there is a kind of information beyond what the physical facts can yield – so that physicalism is false. But does that follow?
