Physicalism: Identity Theory and Functionalism

Substance Dualism and the “Problem of Causation”

Substance dualism (review from earlier lectures):
- Posits two fundamentally different “substances”:
- Immaterial mind/soul.
- Material/physical body.
- Core difficulty: causal interaction.
- How can an immaterial entity push, pull, or otherwise influence material stuff?
Proposed escape route: eliminate the immaterial entirely ➜ embrace Physicalism / Materialism.

Core claim: Everything that exists is physical. No extra “mind-stuff”.
Mental phenomena (thoughts, desires, memories, etc.) are wholly constituted by physical processes.
- Example: “My desire for lunch” is ultimately a particular configuration of chemicals, hormones, electrical events, and H_2O molecules in the brain.
Varieties of physicalist theory mentioned in the course:
- Logical Behaviourism (not covered in detail today; see hand-out for references).
- Identity Theory (today’s focus).
- Functionalism (introduced later in the lecture as a response to problems with Identity Theory).

Slogan: Mental states = Physical states. (Equality sign read as strict identity, not mere correlation.)
Illustrative case:
- Mental token: “I’m going to Paris next week.”
- There exists one, and only one, specific physical state of my brain/body that is that thought.
Physicalist entailment:
- If you create two organisms that are physically indiscernible all the way down, then they must be psychologically indiscernible.

Identity Theory is reductionist:
- Every psychological description can, in principle, be exhaustively re-described in purely physical vocabulary (chemistry, neurobiology, sub-atomic physics, etc.).

Analogy	Inquiry	Philosophical Term
“How many individual dogs were at Crufts?”	Counting each unique dog	Tokens
“How many breeds were at Crufts?”	Counting kinds/species	Types

Claim: For every particular mental event, there exists a particular physical realiser.
- Example: “My tummy-ache at 2 p.m. yesterday” ≡ “That specific pattern of gastric nerve firings at 2 p.m.”
Relatively modest: Does not assert any global, across-organism mapping.

Stronger thesis: A kind of mental state (pain, joy, envy, …) is numerically identical with a kind of neural/physical state.
- Textbook illustration: \text{Pain} \equiv \text{C-fiber stimulation}.
Empirical pay-off: becomes a genuine research programme—discover the neural type for every mental type.

Ontological economy: no spooky immaterial realm.
Scientific synergy: brain science can (and should) explain psychology.
Methodological clarity: look to neurology, pharmacology, etc., to solve mental puzzles.

Hilary Putnam’s critique: Type Identity is “chauvinistic”—it privileges one biological make-up (viz. the human nervous system).

Octopus Pain
- Octopi have markedly different neurochemistry.
- Intuitive verdict: they can feel pain.
- Conflict: they lack “C-fibers”.
Wooden-brained Aliens
- Hypothetical race whose cognition is mediated by wooden, not carbon-based, structures.
- Behavioural evidence suggests genuine intelligence and aversive experience.
Intra-species variability
- Even among humans, neural architectures may differ subtlely (developmental, genetic, prosthetic augmentation).

A single mental type can be realised by many different physical states depending on the organism.
- This is the principle of Multiple Realisability.
Consequence: The naive Type Identity claim (“Pain = C-fiber firing”) cannot be universally true.
- Either we restrict the claim to humans (weakening its explanatory reach) or abandon strict type identity.

Worry about speciesism (psychological “chauvinism”)—doctrines that exclude non-human entities from the mental realm based solely on biochemical differences.
Ethical stakes:
- If octopi or aliens can genuinely suffer, we owe them moral consideration, regardless of neuronal composition.
Methodological lesson:
- Neuroscience alone might offer an incomplete account of mentality; we must also consider the functional role a state plays.

Putnam’s positive proposal: focus on what mental states do rather than what they’re made of.
- Characterise pain by its causal/functional role (e.g., reliably produced by tissue damage, leading to avoidance behaviours, etc.).
Allows diverse physical implementations—human brains, octopus ganglia, silicon chips, wooden alien brains—so long as the functional organisation matches.

Substance Dualism ➜ causal worries.
Physicalism says: only physical stuff.
Identity Theory: mental = physical.
- Token vs. Type identity distinction.
- Reductionist, promises scientific unification.
Putnam (1967): Multiple Realisability challenge.
- Octopus, alien, intra-human variability.
- Identity Theory looks too narrow / chauvinistic.
Functionalism emerges as an alternative: individuate mental states by function, not composition.

Re-read Putnam’s 1967 paper for detailed argumentation.
Clarify the Token/Type distinction with your own examples (e.g., belief at time t vs. the kind belief).
Think through ethical corollaries: if we discover non-standard neural architectures (A.I. or biotech hybrids), how should we evaluate their mental states?
For further context, consult hand-out references on Logical Behaviourism to see how earlier physicalist attempts differed.