---
title: Philosophy of Mind
sort: 140
section-id: metaphysics
description: Dualism, functionalism, physicalism, qualia, and the hard problem of consciousness.
language: en
---

# Philosophy of Mind

Philosophy of mind asks what the mind is, how mental states relate to physical states, and whether consciousness can be explained by the natural sciences. It is a meeting point of metaphysics, epistemology, cognitive science, and neuroscience — and at its centre lies what David Chalmers called *the hard problem of consciousness*, the question of why there is subjective experience at all.

## Substance Dualism

Descartes' *substance dualism* holds that mind and body are distinct substances: the body is extended substance (res extensa), governed by mechanical laws; the mind is thinking substance (res cogitans), unextended and not subject to physical laws ^[Descartes, R., *Meditations*, AT VII:78-80; *The Passions of the Soul*, AT XI:330].

Substance dualism captures the intuition that mental life — the experience of pain, the feeling of red, the taste of coffee — is radically different in kind from the physical world. No description in purely physical terms seems to capture what it is like to be in pain.

The central objection: *causal interaction*. If mind and body are distinct substances, how do they causally interact? How does my decision to raise my arm cause my arm to rise? Descartes' attempted answer — via the pineal gland — was never convincing. Occasionalism (Malebranche) and pre-established harmony (Leibniz) were developed as alternatives, both of which deny genuine causal interaction and invoke God.

## Behaviourism and Its Failures

*Logical behaviourism* — associated with Ryle and early Wittgenstein — held that mental concepts are analysable in terms of behavioural dispositions, not inner states ^[Ryle, G., *The Concept of Mind*, 1949]. To believe that it will rain is to be disposed to carry an umbrella, to seek shelter, and so on. There is no "ghost in the machine" — mentality just is the complex of behavioural dispositions.

Hilary Putnam argued that behaviourism fails because behavioural dispositions are mediated by other mental states ^[Putnam, H., "Brains and Behavior", 1963]. The pain-disposition to withdraw from stimuli requires the desire to avoid pain; the belief-disposition to seek shelter requires the desire to stay dry. No purely behavioural analysis of a mental state can avoid this regress.

## Identity Theory

*Identity theory* — associated with Place and Smart — held that mental states are identical to brain states: pain is a type of neural activity ^[Place, U.T., "Is Consciousness a Brain Process?", *British Journal of Psychology* 47, 1956; Smart, J.J.C., "Sensations and Brain Processes", *Philosophical Review* 68, 1959].

**Multiple realisability objection:** Putnam argued that mental states are *multiply realisable* — they can be realised in many different physical substrates ^[Putnam, H., "Psychological Predicates", 1967]. If octopuses (with radically different nervous systems) can be in pain, pain cannot be identical to any specific neural state. This counts against *type* identity theory, though not *token* identity (this instance of pain is identical to this neural event).

## Functionalism

*Functionalism* — Putnam's alternative — holds that mental states are defined by their *functional role*: their causal relations to sensory inputs, behavioural outputs, and other mental states ^[Putnam, H., "The Nature of Mental States", 1967]. Pain is whatever state is typically caused by tissue damage, causes withdrawal behaviour and the desire to relieve it, and interacts with other states in characteristic ways.

Functionalism accommodates multiple realisability: what makes something a pain is its functional role, regardless of whether it is implemented in neurons, silicon, or anything else. It is the dominant view in philosophy of mind and cognitive science.

**Objections:** The *inverted qualia* argument: two people might have their functional roles entirely aligned while having inverted phenomenal experiences (what's red to you is green to me). Functionalism, which is defined by function, cannot distinguish them. The *absent qualia* argument: a system could have all the right functional relations while having no phenomenal experience at all — a philosophical zombie ^[Block, N., "Troubles with Functionalism", *Minnesota Studies in the Philosophy of Science* 9, 1978; Chalmers, D., *The Conscious Mind*, 1996, ch.3].

## Physicalism and Its Varieties

Contemporary philosophy of mind is broadly physicalist: mental states are physical states or at least entirely dependent on physical states. The question is *how* they are dependent.

*Supervenience physicalism*: mental properties supervene on physical properties — any two individuals physically identical are mentally identical ^[Kim, J., *Supervenience and Mind*, Cambridge UP, 1993].

*Non-reductive physicalism*: mental properties are real but not reducible to physical properties, even though they supervene on them.

*Reductive physicalism*: mental properties can ultimately be explained in physical terms.

The *causal exclusion argument* (Kim) poses a serious problem for non-reductive physicalism: if physical events have sufficient physical causes, and mental events are supposed to cause behaviour, then either mental events are physical events (reductivism) or mental events are causally redundant ^[Kim, J., *Mind in a Physical World*, 1998, ch.2-3].

## The Hard Problem

Chalmers distinguished the *easy problems* of consciousness — explaining cognitive access, attention, introspection, sleep/waking cycles (these problems are hard, but they admit of functional-explanatory solutions) — from *the hard problem*: why is there subjective experience at all? ^[Chalmers, D., "Facing Up to the Problem of Consciousness", *Journal of Consciousness Studies* 2, 1995].

Even a complete physical and functional account of what the brain does would leave open why any of this processing is *experienced* — why it feels like something to be a brain. The explanatory gap between physical descriptions and phenomenal experience seems irreducible.

Responses range from *type-B physicalism* (the gap is a conceptual illusion, not a real explanatory gap) to *property dualism* (phenomenal properties are real, non-physical properties that supervene on physical ones) to *panpsychism* (consciousness is a fundamental feature of reality, found at all levels of physical organisation) ^[Goff, P., *Galileo's Error*, 2019].

The hard problem has not been solved. Whether it is solvable within a physicalist framework, or whether it requires revising our fundamental ontology, remains one of philosophy's most contested open questions.
