Is the mind just the brain?
Is your mind a separate thing, a brain state, a pattern of functions, or the foundation of everything?
I
Substance dualism
The mind is a non-physical thing, distinct from the body, which interacts with it.
- Best argument
- René Descartes argued that he could clearly conceive of his mind existing without his body, since he could doubt that he had a body but not that he was thinking. Whatever can be clearly conceived apart can exist apart, so mind and body are distinct. The view also fits how experience seems from the inside: the self does not feel like a lump of tissue.
- Strongest objection
- Princess Elisabeth of Bohemia put the decisive question to Descartes in 1643: how can an unextended, immaterial soul push a material body? Modern physics sharpens it, since energy appears to be conserved and every physical event seems to have a physical cause, leaving no gap for a soul to act through.
- The reply
- Some dualists respond that the conservation laws apply only to closed systems, or that the mind might act by influencing quantum events without adding energy. Others accept that the interaction is a brute fact, no stranger than gravity acting at a distance once seemed.
- Defended by
- René Descartes, Plato, Richard Swinburne
II
Identity theory
Mental states are brain states. A pain just is a certain pattern of neural activity, as lightning just is electrical discharge.
- Best argument
- Science routinely discovers that two descriptions pick out one thing: water is H2O, heat is molecular motion. The close correlation between mental and brain events is best explained by identity, which is simpler than positing two kinds of thing in lockstep.
- Strongest objection
- If pain is one specific human brain state, then an octopus or an alien with a different nervous system could not feel pain, which seems wrong. Hilary Putnam called this the problem of multiple realisability.
- Defended by
- J. J. C. Smart, U. T. Place, Patricia Churchland
III
Functionalism
A mental state is defined by what it does: its causes, its effects, and its relations to other states. Any system that plays the right roles has a mind.
- Best argument
- Pain is whatever is caused by damage, produces distress and avoidance, and makes you want it to stop. Neurons in humans, different tissue in octopuses, perhaps silicon in robots could all play that role. This explains multiple realisability and fits cognitive science, which models the mind as information processing.
- Strongest objection
- It seems to leave out experience. A system could play every functional role of pain without anything feeling painful. Searle's Chinese Room argues similarly that running the right program is not enough for understanding.
- The reply
- Functionalists answer that the intuition of something left over may itself be a product of how we represent our own minds, and that the Chinese Room confuses a part of the system with the whole.
- Defended by
- Hilary Putnam, Jerry Fodor, Daniel Dennett
IV
Idealism
Reality is fundamentally mental. Matter is either a construction of minds or appearances within them.
- Best argument
- We never encounter matter except through experience. George Berkeley argued that the idea of something existing wholly unperceived is incoherent. Modern versions suggest that what physics describes is the structure of a reality whose intrinsic nature is experiential.
- Strongest objection
- Idealism struggles to explain why the world behaves so regularly when no one is looking, and why it existed for billions of years before any minds evolved.
- The reply
- Berkeley's answer was that God perceives everything continuously. Contemporary idealists appeal instead to a universal consciousness or to the regularities of experience itself.
- Defended by
- George Berkeley, Bernardo Kastrup
Where you stand
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For the full background, variations and open questions, read the entry: Is the mind just the brain?.