Mind, Matter, and Meaning

Identity Theory (Mind-Brain Identity Theory)

The mind-brain identity theory identifies mental states or processes with physical states or processes of the brain. An experience and a brain process are, on this view, one occurrence described in different ways, rather than two occurrences joined by a causal law. Identity is therefore stronger than correlation or causal dependence.

The theory gained a prominent modern formulation in U. T. Place’s “Is Consciousness a Brain Process?” (1956) and J. J. C. Smart’s “Sensations and Brain Processes” (1959). Herbert Feigl developed a related position. These approaches allowed sensations to occur as genuine internal processes while resisting a separate nonphysical domain.

Empirical Identity and Difference in Meaning

Place and Smart compare mental-physical identification with scientific identifications such as lightning with electrical discharge. Someone can recognize lightning while knowing nothing about electricity. Likewise, recognizing an afterimage need not involve knowing its neural nature.

The identity theorist does not therefore claim that an ordinary sensation word and a neuroscientific expression mean the same thing. Different concepts can refer to the same phenomenon. An objection based only on a speaker’s ignorance of neuroscience would not establish that sensation and neural activity must be distinct.

Smart described the proposed identity as contingent and empirically discoverable. Later modal discussions complicate that formulation: an identity discovered empirically may nevertheless hold necessarily if its terms rigidly designate the same entity. The historical terminology should not be silently treated as a resolution of those later questions.

Type and Token Identity

Type identity identifies a mental kind with a physical kind. A strong unrestricted version assigns the same physical kind wherever a particular mental kind occurs. Token identity instead identifies each particular mental occurrence with a physical occurrence without requiring every instance of that mental type to share one physical type.

This distinction separates two claims often compressed into “mental states are brain states.” A functionalist can permit token-level physical identity while identifying mental types by causal roles. Some identity theorists also defend identities relative to a species or system, rather than one unrestricted identity across all possible organisms.

“Pain is C-fiber firing” is a familiar classroom illustration, not an established universal neuroscientific identity or a complete statement of every historical identity theorist’s position. The substantive theory requires an independently supported account of the relevant physical process.

Smart’s Topic-Neutral Strategy

A report of a yellow-orange afterimage seems to mention a quality not found in a brain process. Smart proposes describing the experience in topic-neutral language: something occurs like what occurs when the person sees an illuminated orange under ordinary conditions. Such a description does not decide in advance whether the occurring process is physical or nonphysical.

Smart also distinguishes the experience from an alleged colored internal object. Identifying an experience with a brain process does not require a surgeon to find a yellow-orange patch in the brain. Critics reply that topic-neutral reformulation may still leave the qualitative character unexplained. The strategy blocks certain immediate objections to identity without supplying a complete empirical theory of experience.

Parsimony provides another motivation. If sensations were additional nonphysical events, extra psychophysical laws would be required to connect them to neural activity. Identity theorists argue that identification avoids these additional laws. Opponents maintain that explanatory economy cannot override evidence for irreducible properties.

Multiple Realizability

Functionalists argue that different organisms, and possibly artificial systems, could share mental states despite different physical implementations. If pain can occur in several physical kinds, an unrestricted identity between pain and one neural kind appears too restrictive.

Identity theorists can question whether the cases instantiate exactly the same mental type, defend more local identities, or argue that the apparent variety conceals a common physical characterization. Whether such moves preserve informative scientific identities is debated. Multiple realizability is consequently a major objection to certain type identities, not an automatic refutation of every mental-physical identity claim.

Phenomenal and Externalist Objections

Knowledge and conceivability arguments ask whether complete physical knowledge or a physical duplicate could still leave experience out. Identity theorists distinguish concepts from referents and challenge the inference from apparent separability to genuine possibility. Critics contend that these replies do not explain why sensation has its particular felt character.

Semantic externalism supplies another pressure: some beliefs are individuated partly by relations to an environment or community, while a narrowly described brain state does not include those relations. An identity account must specify its scope rather than assume that a successful account of sensations automatically applies to every belief.

The continuing dispute concerns which identities evidence supports, at what explanatory level, and whether physical identification also adequately explains phenomenal character and content.

Further Reading

  • Smart, J. J. C. 1959. “Sensations and Brain Processes.” The Philosophical Review 68 (2): 141–156.
  • Place, U. T. 1956. “Is Consciousness a Brain Process?” British Journal of Psychology 47: 44–50.
  • Smart, J. J. C. “The Mind/Brain Identity Theory.” Stanford Encyclopedia of Philosophy. Revised May 18, 2007.
  • Physicalism.md|Physicalism — physicalist theses beyond mind-brain identity.
  • Functionalism.md|Functionalism — role identity and multiple realizability.
  • Behaviorism.md|Behaviorism — alternative analyses of mental vocabulary.
  • The Explanatory Gap.md|The Explanatory Gap — physical identification and phenomenal explanation.
  • Mind, Matter, and Meaning — Gordon Swobe’s book presents the author’s argument about mind, consciousness, and meaning.