Mind, Matter, and Meaning

David Lewis

David Lewis (1941–2001) was an American philosopher whose work ranged across metaphysics, language, logic, and philosophy of mind. His accounts of mental states combine functional characterization with identification of the states realizing those roles. His ability hypothesis offers a physicalist response to the claim that experience teaches facts unavailable through complete physical knowledge.

Major Works in Philosophy of Mind

  • “An Argument for the Identity Theory” (1966) argues from the causal roles of mental states to psychophysical identification.
  • “Psychophysical and Theoretical Identifications” (1972) develops the use of implicit theoretical definitions.
  • “Mad Pain and Martian Pain” (1980) examines atypical human pain and differently realized extraterrestrial pain.
  • “What Experience Teaches” (1988) defends the ability hypothesis concerning phenomenal knowledge.

His wider metaphysical work includes On the Plurality of Worlds (1986). The arguments about mind should not be treated as dependent on accepting his entire theory of concrete possible worlds.

Functional Roles and Their Realizers

Lewis begins with a network of commonsense psychological claims connecting beliefs, desires, sensations, stimuli, and behavior. Mental terms are treated as implicitly defined by their roles within this theory. Replacing the terms with variables allows the theory to characterize whatever states jointly occupy those roles.

A distinction is essential: a role is a causal specification; a realizer is the state that fills it. Lewis’s identity approach identifies mental states with the relevant realizers, not simply with abstract roles. Empirical inquiry can then discover which physical states perform the roles in an appropriate population. The functional characterization and physical identification do different work.

This allows a mind–brain identity theory without requiring one physiological type for every possible creature. What normally realizes pain in humans may differ from what realizes it in another species. Multiple realization does not, on Lewis’s account, erase the importance of the realizing state.

Mad Pain and Martian Pain

The mad-pain case concerns someone whose pain has unusual causes and effects. It need not lead to the ordinary avoidance behavior or result from typical injury. If pain were determined solely by the individual’s present functional role, the case would threaten the claim that this person is in pain.

The Martian case supplies the opposite pressure. A creature’s pain has familiar causes and effects but is realized by hydraulic mechanisms rather than human neural tissue. An unqualified species-independent identity with one human neural state would exclude the Martian.

Lewis relativizes realization to appropriate populations. The atypical human can have the state that normally plays the pain role in humans, even though it plays an unusual role in that individual. The Martian can have a different physiological state that normally plays the corresponding role in Martians. Atypicality within a population and variation between populations therefore receive different treatment.

Critics ask how to identify the relevant population, especially for unique artificial systems or borderline cases. Lewis’s proposal provides a strategy for accommodating variation, not a mechanical procedure that removes every question about pain attribution.

What Experience Teaches

The knowledge argument imagines Mary possessing every physical fact about color vision while having no color experience. On release, she seems to learn what seeing red is like. The antiphysicalist conclusion treats this as discovery of an additional nonphysical fact.

Lewis, following Laurence Nemirow, proposes that knowing what an experience is like consists in abilities to remember, imagine, and recognize it. Tasting Vegemite for the first time can enable a person to recall its taste, imagine it later, and recognize a recurrence. A description need not confer these abilities merely by stating all the relevant facts.

Lewis distinguishes phenomenal information from these acquired capacities. He does not deny that experience can also teach ordinary facts: someone may learn that a particular food tastes a certain way or recognize which food they were given. His claim is that the specifically phenomenal gain need not consist in information concerning a further property beyond the physical facts.

The ability hypothesis therefore accepts a substantial change in Mary while rejecting the interpretation required for the knowledge argument. It does not claim that experience teaches nothing or that an ability is itself a mysterious nonphysical addition.

Objections and Replies

Propositional learning. Critics argue that Mary gains a true thought about how an experience feels, not just new skills. Ability theorists ask whether this thought expresses a new fact or deploys the newly acquired capacities. Other physicalists accept new propositional knowledge while holding that it concerns an old physical fact under a new mode of presentation. That alternative should not be equated with Lewis’s hypothesis.

Ability dissociations. Imagination, recognition, and memory can vary independently. A person may know an experience while having limited ability to imagine it. This challenges an overly strict list of jointly necessary abilities. Defenses refine the relevant ability or distinguish normal manifestations from the underlying competence. Such refinements require argument; calling all phenomenal knowledge “know-how” does not alone establish them.

Inverted and absent experience. Critics of functional theories argue that a system might occupy the roles while feeling differently, or feel nothing. Lewis’s account addresses some atypical and cross-species cases through population-relative realizers. Whether it captures every phenomenal contrast remains disputed.

Folk psychology. The initial theory might contain errors or fail to uniquely identify a set of occupants. This threatens implicit definition unless the account allows sufficiently accurate approximations or revisions. The strength of the approach is its systematic treatment of interrelated mental terms; its vulnerability is dependence on the adequacy of that system.

  • Functionalism — roles and physical realizers.
  • Identity Theory — psychophysical identification.
  • Mary's Room — the knowledge argument and the ability hypothesis.
  • Qualia — phenomenal character and functional characterization.
  • Jackson — the originator of the Mary argument.
  • Block — challenges to functional accounts of consciousness.

Further Reading

  • Lewis, David. “An Argument for the Identity Theory.” The Journal of Philosophy 63 (1966): 17–25.
  • Lewis, David. “Psychophysical and Theoretical Identifications.” Australasian Journal of Philosophy 50 (1972): 249–258.
  • Lewis, David. “Mad Pain and Martian Pain.” In Readings in Philosophy of Psychology, vol. 1, edited by Ned Block. Harvard University Press, 1980.
  • Lewis, David. “What Experience Teaches.” Proceedings of the Russellian Society (1988); reprinted in Papers in Metaphysics and Epistemology. Cambridge University Press, 1999, pp. 262–290.

Mind, Matter, and Meaning presents the site author’s arguments about mind and meaning. It is a separate argumentative work, not a neutral source for the account above.