Materialism › Mind-Brain
Lewis’s Analytic Functionalism and Causal-Role Identity Theory
Experiences as the Physical Occupants of Causal Roles
Lewis defines each experience by the causal role folk psychology assigns it (its typical causes, effects, and links to other mental states) and then lets science discover which physical state fills that role, usually a neural state. Pain is whatever occupies the pain role, so pain is that neural state. Qualia are real but are the occupants of functional roles, and knowing what an experience is like is a set of abilities, not knowledge of a nonphysical fact.
David Lewis
What consciousness is
An experience is the physical state, typically neural, that occupies the causal role folk psychology defines for it. Pain is the state typically caused by damage and typically causing aversion.
Mind and body
Psychophysical identity reached by argument. If pain is by definition the occupant of role R and neural state N occupies R, then pain is N by transitivity of identity. The identities are contingent and relative to a population, so human pain and Martian pain can be different physical states.
Mechanism
A two-step reduction. First define a mental state as the unique occupant of a causal role by Ramseyfying folk psychology, then identify that occupant empirically with a physical state.
Core claims
- Folk psychology works as an implicit theory whose mental terms are defined together by the causal network it postulates.
- The identity of pain with a neural state follows by transitivity once science finds the occupant of the pain role.
- In ‘Mad Pain and Martian Pain,’ relativizing roles to populations lets a madman with atypical pain and a Martian with hydraulic pain both count as being in pain.
- The ability hypothesis answers Jackson’s knowledge argument by treating knowing what an experience is like as know-how, not knowledge of a fact.
- Lewis answers ‘yes and no’ to whether a materialist should believe in qualia, accepting physical states that imperfectly deserve the name.
Criticisms
Conee and Alter argue that abilities and phenomenal knowledge can come apart, so one can be kept without the other, which undercuts the ability hypothesis. Dualists and physicalists who accept a genuine epistemic gap both contest Lewis’s two reclassifications: phenomenal knowledge as know-how and introspective access as something other than revelation.
Implications
- AI consciousness: Possible
- Lewis allows the same role to be filled by different hardware in different populations, as with Martian pain, so an artificial system whose states occupy the right causal roles could have experiences.
- Survival beyond death: No
- Since every experience is a physical state of the organism, it follows from the view that experience ends when those states cease.
- Meaning and purpose: Humanistic only
- The view is a thoroughgoing materialism with no place for cosmic purpose in the account of mind.
- Virtual immortality: Uncertain
- A copy realizing the same roles might count as having the same kinds of states, but Lewis did not address uploading, and role occupancy is relative to populations.
Related theories
- Smart’s Topic-Neutral Identity (Influence)
- Armstrong’s Causal-Role Central-State Materialism (Overlap)
- Putnam’s Machine Functionalism (Contrast)
- Jackson's Representationalism and the Knowledge Argument (Critique)
Sources
- An Argument for the Identity Theory, David Lewis (1966)
- How to Define Theoretical Terms, David Lewis (1970)
- Psychophysical and Theoretical Identifications, David Lewis (1972)
- Mad Pain and Martian Pain, David Lewis (1980)
- What Experience Teaches, David Lewis (1988)
- Reduction of Mind, David Lewis (1994)
- Should a Materialist Believe in Qualia?, David Lewis (1995)
- Epiphenomenal Qualia, F. Jackson (1982)
- Physicalism and the Cognitive Role of Acquaintance, L. Nemirow (1990)
- Phenomenal Knowledge, E. Conee (1994)
- Know-How, Ability, and the Ability Hypothesis, T. Alter (2001)