Mind-Brain Type Identity Theory | AQA A-Level Philosophy
For Specification 7172
AQA A-Level Philosophy | Free Revision Notes
Estimated study time: 65 to 75 minutes
This Mind-Brain Type Identity Theory A-Level Philosophy revision lesson examines a reductive physicalist theory according to which types of mental state are identical to types of brain or neural state. Unlike Physicalism and Philosophical Behaviourism [Physicalism and Philosophical Behaviourism], identity theory does not reduce mental-state language to behavioural language. Instead, it makes an ontological reduction, claiming that mental and brain states are actually the same kind of phenomenon. You will also apply the specified dualist arguments and examine the multiple-realisation objection.
Learning Objectives 🎯
By the end of this revision page, you should be able to:
Explain the claim that mental-state types are identical to brain-state types.
Distinguish ontological reduction from analytical reduction.
Apply the specified dualist arguments to mind-brain type identity theory.
Explain the multiple-realisation objection.
Evaluate whether mind-brain type identity theory gives an adequate physicalist account of mental states.
Revision Notes 📚
Mind-Brain Type Identity Theory A-Level Philosophy Revision: the central claim
Mind-brain type identity theory is a reductive physicalist theory.
It claims that:
Types of mental states are ontologically identical to types of brain or neural states.
So a type of mental state is not a separate non-physical phenomenon that merely accompanies a brain state.
The theory claims that the mental-state type and the brain-state type are, in reality, the same type of phenomenon.
What is a brain state?
A brain state is a physiological state or process of the brain, such as a pattern of neural activity.
Mind-brain type identity theory claims that mental states can be ontologically reduced to such brain states.
The theory is therefore firmly within physicalism.
Physicalists reject genuinely non-physical mental substances or properties and attempt to explain mentality within a physical account of reality.
What does "type identity" mean?
The theory concerns types of mental state and types of brain state.
The claim is:
mental-state type X = brain-state type Y
For example, if a particular type identity could be established, what appears to be a mental phenomenon and what appears to be a neural phenomenon would actually be one and the same kind of phenomenon.
The theory is not merely saying:
Mental states are caused by brain states.
Nor is it saying:
Mental states occur alongside brain states.
Its claim is stronger:
Mental-state types are brain-state types.
Identity is stronger than correlation
This distinction is crucial.
Suppose mental state M always occurs when brain state B occurs.
That would establish a correlation.
But identity theory claims:
M is B.
So it does not posit two events that reliably occur together.
It claims that what we describe mentally and what we describe neurologically are ontologically the same type of state.
Identity theory and physicalism
Recall from Physicalism and Philosophical Behaviourism [Physicalism and Philosophical Behaviourism] that physicalism holds that everything is physical or supervenes upon the physical.
Mind-brain type identity theory offers a particularly strong form of physical reduction.
Mental states are not merely dependent upon physical states.
They are claimed to be identical with brain states.
This gives:
mental state type = physical brain state type
The theory therefore rejects both:
separate non-physical mental substances
irreducibly non-physical mental properties
Ontological Reduction
What is ontological reduction?
An ontological reduction claims that two apparently different phenomena are actually the same kind of phenomenon.
If X is ontologically reducible to Y:
X and Y are in fact the same type or kind of phenomenon.
Applied to identity theory:
mental-state types are identical to brain-state types.
What is true of mental states and their properties is therefore reducible to what is true of physical brain states and their properties.
The identity claim
The theory can therefore be represented as:
Mental-state type X
=
Brain-state type Y
This is an ontological claim.
It concerns what the mental state actually is.
The identity theorist claims that once the relevant brain-state identity is established, no additional non-physical mental state is required.
Analytical Reduction
What is analytical reduction?
An analytical reduction concerns language and meaning, not ontological identity.
One type of language is analytically reducible to another if it can be translated into the other without loss of meaning.
This was central to philosophical behaviourism.
For example, behaviourism attempts to translate propositions about mental states into propositions about:
bodily behaviour
behavioural dispositions
The reduction concerns what the propositions mean.
Identity theory is not analytically reductive
AQA specifies that mind-brain type identity theory is:
ontologically, but not analytically, reductive.
This means that:
mental-state type X and brain-state type Y can be the same phenomenon
without:
"mental state X" and "brain state Y" meaning the same thing.
The terms are therefore not synonymous.
This distinction is essential.
Ontological and analytical reduction compared
Ontological reduction | Analytical reduction |
Concerns what phenomena actually are | Concerns language and meaning |
X and Y are the same kind of phenomenon | Language about X can be translated into language about Y without loss of meaning |
Central to mind-brain type identity theory | Central to philosophical behaviourism |
Mental-state types are brain-state types | Mental-state language is translated into behavioural language |
Mind-brain type identity theory accepts the left-hand form of reduction but not the right-hand one.
Why the difference matters
Suppose someone says:
"Pain is identical to a particular type of brain state."
According to identity theory, this could be ontologically true even if:
"pain"
and:
"that brain state"
do not have the same meaning.
Identity theory therefore does not need to claim that ordinary mental vocabulary is simply another way of saying exactly the same thing as neurological vocabulary.
Its claim concerns reality rather than linguistic synonymy.
Identity Theory Compared with Philosophical Behaviourism
The distinction from Physicalism and Philosophical Behaviourism [Physicalism and Philosophical Behaviourism] is fundamental.
Philosophical behaviourism
Behaviourism asks:
What do propositions about mental states mean?
It answers in terms of:
behaviour
behavioural dispositions
This is an analytical approach.
Mind-brain type identity theory
Identity theory asks:
What are mental states?
It answers:
They are brain states.
This is an ontological approach.
The contrast can therefore be summarised as:
Behaviourism: mental language → behavioural language
Identity theory: mental states = brain states
This means identity theory avoids some of the difficulties specific to behavioural reduction.
For example, it does not need to claim that the mental state is identical with the behaviour studied in Super-Spartans and Perfect Actors [Super-Spartans and Perfect Actors].
Applying Dualist Arguments to Identity Theory
AQA requires dualist arguments applied to mind-brain type identity theory.
The dualist arguments studied earlier attempt to establish that mental reality cannot be reduced to the physical.
If successful, they therefore directly threaten the identity theorist's claim:
mental-state type = physical brain-state type
Descartes' indivisibility argument
In Descartes' Indivisibility Argument [Descartes' Indivisibility Argument], Descartes argues that:
bodies are divisible
minds are not divisible
therefore mind cannot be identical to body or a part of the body
If the argument succeeds, it creates a direct problem for identity theory.
Brain states are physical states.
If the mental is genuinely distinct from the physical because their essential characteristics differ, then mental-state types cannot simply be brain-state types.
The dualist can therefore argue:
Mental and physical reality have different essential characteristics.
Identical things cannot differ in their essential characteristics.
Therefore, mental states are not identical to physical brain states.
Mind-brain type identity theory is false.
The force of this objection depends upon the success of Descartes' original argument and the responses considered in that lesson.
Descartes' conceivability argument
Descartes' Conceivability Argument [Descartes' Conceivability Argument] can also be applied.
If it is genuinely conceivable and metaphysically possible for mind to exist without body, then mental reality cannot be identical to physical bodily reality.
Applied to identity theory:
A mental state is claimed to be identical to a physical brain state.
If the mental could exist without the relevant physical state, the two could not be identical.
The conceivability argument claims that mental reality can exist independently of bodily reality.
Therefore, if that argument succeeds, mind-brain identity is undermined.
Again, the identity theorist can use the earlier responses:
mind without body may not be conceivable
conceivability may not entail metaphysical possibility
metaphysical possibility may not establish the relevant conclusion about the actual world
Property dualism applied to identity theory
Property Dualism [Property Dualism] provides another direct challenge.
Property dualism claims that at least some mental properties are not reducible to physical properties.
Mind-brain type identity theory claims the opposite type of reduction:
mental states and their properties are ultimately reducible to physical brain states and their properties.
The debate therefore centres on whether phenomenal and intentional features of mental states can be captured by the physical identity.
Chalmers' philosophical zombies
Chalmers' Philosophical Zombies [Chalmers' Philosophical Zombies] can be applied to identity theory.
A philosophical zombie is supposed to be physically identical to a conscious human while lacking consciousness or qualia.
If such a being is genuinely metaphysically possible, then:
all the physical brain facts could remain the same
while:
phenomenal mental properties differed.
That would challenge the claim that phenomenal mental states simply are physical brain states.
If the physical state were genuinely identical to the phenomenal state, one could not remain present while the other was absent.
The identity theorist can therefore resist the argument using the specified responses to Chalmers, especially by challenging zombie conceivability or the move from conceivability to metaphysical possibility.
Jackson's Knowledge/Mary argument
Jackson's Knowledge/Mary Argument [Jackson's Knowledge/Mary Argument] can also challenge reductive identity theory.
Mary knows all the physical facts about colour and colour vision.
When she first experiences colour, Jackson argues that she learns something new about phenomenal experience.
If she already knew every physical fact but still lacked a fact about the mental state, then mental facts cannot all simply be physical brain facts.
This would threaten the identity theorist's ontological reduction.
However, the physicalist responses remain available:
ability knowledge
acquaintance knowledge
New Knowledge/Old Fact
If one of these responses succeeds, Mary does not establish an additional non-physical property.
Does Identity Theory Avoid Behaviourism's Problems?
Identity theory differs significantly from philosophical behaviourism.
It does not claim:
pain = pain behaviour
or:
pain-language = behavioural-language.
Instead it claims:
pain-type = brain-state type
This means objections such as Super-Spartans and perfect actors do not directly target identity theory in the same way.
A person could suppress their behaviour while still being in the relevant brain state.
A perfect actor could reproduce behaviour without being in that brain state.
Identity theory therefore separates the mental state from its outward behavioural expression.
However, the theory faces its own distinctive problem:
multiple realisation.
The Multiple-Realisation Objection
What is multiple realisation?
For mind-brain type identity theory, multiple realisability is the claim that:
The same mental state can be instantiated by different physical processes, possibly an unlimited number.
This challenges the idea that one type of mental state is identical with one type of brain state.
Why it threatens type identity
Identity theory claims:
mental-state type M = brain-state type B
But multiple realisability proposes:
mental-state type M can be instantiated by physical process B1
and:
mental-state type M can also be instantiated by physical process B2
and potentially:
B3, B4, B5...
If the physical realisations are genuinely different types of physical process, then it becomes difficult to maintain that M is identical to one particular physical type.
The structure of the objection
The argument can be reconstructed as follows:
Mind-brain type identity theory claims that each relevant type of mental state is identical with a type of brain state.
The same mental-state type can be instantiated by different physical processes.
Therefore, the same mental-state type cannot simply be identical with one specific type of physical process.
This challenges mind-brain type identity theory.
The objection targets the word type in type identity theory.
Multiple realisability here is different from behaviourism
This distinction is extremely important.
In Further Problems for Behaviourism [Further Problems for Behaviourism]:
the same mental state could be expressed in many different behaviours.
For mind-brain type identity theory:
the same mental state could be instantiated by many different physical processes.
So:
Behaviourism | Identity theory |
One mental state, many behavioural expressions | One mental state, many physical realisations |
Challenges behavioural reduction | Challenges mental-type to brain-type identity |
Do not mix these two objections in an exam.
Why the objection is significant
Suppose identity theory requires:
Mental state M is identical to physical state P.
If M can occur through a different physical process Q, then:
M = P
cannot straightforwardly account for:
M realised by Q.
The type identity appears too restrictive.
The objection therefore claims that mentality may be physically realised in more than one way.
Can the identity theorist resist multiple realisation?
The identity theorist can challenge the central claim.
If apparently different examples of the same mental state are actually different mental-state types, then the required one-to-one type identities may still be preserved.
However, this response needs justification.
The multiple-realisation objection gains force precisely from the claim that it is genuinely the same mental-state type despite differences in the physical process that instantiates it.
The debate therefore turns on whether mental-state types can legitimately be classified independently of one particular physical realisation.
Evaluating Mind-Brain Type Identity Theory
Strength: it provides a direct physicalist account
Identity theory gives a clear account of mental states.
Rather than introducing:
a separate mental substance
irreducible mental properties
it identifies mental-state types with physical brain-state types.
This is consistent with physicalism because mental reality is ontologically reduced to physical reality.
Strength: it does not reduce mentality to behaviour
The theory avoids the specific behaviourist claim that mental-state language is equivalent to behavioural language.
This means it is not directly threatened by the fact that:
mental states may exist without expected behaviour
behaviour may occur without the genuine mental state
Those problems motivated the move beyond Super-Spartans and Perfect Actors [Super-Spartans and Perfect Actors].
Identity theory locates the mental state in the physical brain state rather than the outward behaviour.
Strength: it avoids Cartesian interaction between distinct substances
If mental states simply are physical brain states, there is no need to explain causal interaction between a non-physical mental substance and an extended physical body.
The Problems for Interactionist Dualism [Problems for Interactionist Dualism] arose because mind and body were treated as ontologically distinct while also causally interacting.
Identity theory rejects that separation.
Mental causation can therefore be understood as physical causation because the mental state is itself physical.
Problem: dualist arguments deny the required identity
The major dualist arguments challenge the theory at its foundation.
If Descartes establishes that mind is distinct from physical body, type identity cannot be true.
If Chalmers establishes that physical duplication need not involve phenomenal duplication, phenomenal mental states cannot simply be physical states.
If Jackson establishes that complete physical knowledge leaves out phenomenal facts, physical reduction is incomplete.
Identity theory therefore depends upon physicalist responses to these dualist arguments.
Problem: multiple realisation attacks type identities directly
The multiple-realisation objection is particularly important because it targets the distinctive form of the theory.
Type identity requires correspondences between:
types of mental state
and:
types of physical brain state.
But if one mental-state type can be instantiated in different physical processes, a single type identity may not be available.
This is not merely a difficulty identifying the correct brain state.
It challenges whether the required type identity exists at all.
Does failure to find an identity prove dualism?
No.
Suppose multiple realisability successfully undermines mind-brain type identity theory.
The conclusion would be:
Mental-state types cannot be identified with particular brain-state types in the way proposed by type identity theory.
It would not automatically establish:
Mental states are non-physical.
Another physicalist account may still be possible.
This becomes particularly important in Functionalism [Functionalism], which explicitly allows the same mental state to be multiply realised.
So:
Type identity theory false ≠ dualism true
Comparing Behaviourism and Identity Theory
The move from behaviourism to identity theory can be summarised clearly.
Philosophical behaviourism | Mind-brain type identity theory |
Physicalist theory | Physicalist theory |
Focuses on mental-state language | Focuses on the ontology of mental states |
Analytical reduction | Ontological reduction |
Mental language reduced to behavioural language | Mental-state types identified with brain-state types |
Challenged by Super-Spartans, perfect actors, circularity, behavioural multiple realisability and asymmetry | Challenged by dualist arguments and physical multiple realisation |
Both attempt to account for mentality physically, but they do so in fundamentally different ways.
Preparing for Later Physicalist Theories
Mind-brain type identity theory is not the final physicalist theory in the course.
Eliminative Materialism [Eliminative Materialism] takes a more radical approach by questioning whether some or all common-sense mental states exist at all.
Later, Functionalism [Functionalism] characterises mental states by their functional roles and explicitly allows multiple realisation.
These theories respond differently to the difficulties encountered by behaviourism and identity theory.
What You Need to Be Able to Do in an Examination
For this topic, you should be able to:
define mind-brain type identity theory
explain what a brain state is
explain the claim that mental-state types are brain-state types
distinguish identity from mere correlation or causation
define ontological reduction
define analytical reduction
explain why identity theory is ontologically but not analytically reductive
distinguish identity theory from philosophical behaviourism
apply Descartes' Indivisibility Argument [Descartes' Indivisibility Argument]
apply Descartes' Conceivability Argument [Descartes' Conceivability Argument]
apply the relevant property-dualist arguments
explain multiple realisability in terms of different physical processes
distinguish physical multiple realisability from behavioural multiple realisability
evaluate whether multiple realisation undermines type identities
recognise that rejecting type identity theory does not automatically establish dualism
The central claim to test is:
Can each type of mental state genuinely be identified with a type of physical brain state?
Key Words 🔑
Key word | Student-friendly definition | How it may be used in an exam |
Mind-brain type identity theory | The reductive physicalist theory that types of mental states are ontologically, but not analytically, identical to types of brain states. | Define the theory and establish the claim being evaluated. |
Brain state | A physiological state or process of the brain, such as a pattern of neural activity. | Explain what the identity theorist claims mental-state types are identical with. |
Ontological reduction | The claim that two apparently different phenomena are in fact the same type or kind of phenomenon. | Explain the sense in which mental states are reduced to brain states. |
Analytical reduction | Translation of one form of language into another without loss of meaning. | Explain what identity theory does not claim and contrast it with behaviourism. |
Multiple realisability | The claim that the same mental state can be instantiated by different physical processes. | Explain the main specified objection to the proposed mental-brain type identities. |
Hints from the Examiner Reports 💡
No lesson-specific examiner guidance was identified in the provided reports.
Common Mistakes ⚠️
Mistake: Saying identity theory claims brain states cause mental states
Why this is incorrect:Identity theory does not posit two separate states connected by causation. It claims that the mental-state type is identical to the brain-state type.
How to improve:Use the formula:
mental-state type = brain-state type
not:
brain state → mental state
Mistake: Saying "mental state" and "brain state" mean the same thing
Why this is incorrect:AQA specifies that the reduction is ontological but not analytical.
How to improve:State that the phenomena can be identical without the terms being synonymous.
Mistake: Confusing identity theory with philosophical behaviourism
Why this is incorrect:Behaviourism analytically reduces mental-state language to behavioural language. Identity theory ontologically reduces mental states to brain states.
How to improve:Remember:
behaviourism = language
identity theory = ontology
Mistake: Using the wrong multiple-realisability objection
Why this is incorrect:For behaviourism, the issue is many possible behaviours expressing the same mental state. For type identity theory, it is different physical processes instantiating the same mental state.
How to improve:Always specify what is doing the realising.
Mistake: Saying multiple realisation automatically proves property dualism
Why this is incorrect:The objection challenges a particular physicalist theory, not physicalism as a whole.
How to improve:Conclude only that the proposed type identity is threatened. Other physicalist theories remain possible.
Exam-Style Questions ✍️
Question 1
Define mind-brain type identity theory.(3 marks)
Question 2
What is ontological reduction?(3 marks)
Question 3
Explain why mind-brain type identity theory is ontologically but not analytically reductive.(5 marks)
Question 4
Explain one way in which a dualist argument can be applied to mind-brain type identity theory.(5 marks)
Question 5
Explain the multiple-realisation objection to mind-brain type identity theory.(5 marks)
Question 6
A philosopher claims:
"If pain is identical with one type of physical brain state, then anything genuinely in pain must instantiate that physical type."
Explain how multiple realisation challenges this claim.(12 marks)
Question 7
Explain and compare philosophical behaviourism and mind-brain type identity theory as reductive physicalist theories.(12 marks)
Question 8
Is mind-brain type identity theory an adequate account of mental states?(25 marks)
Indicative Answers and Marking Guidance
Question 1
Mind-brain type identity theory is a reductive physicalist theory claiming that types of mental states are ontologically, but not analytically, identical to types of brain or neural states.
The mental-state type and brain-state type are therefore claimed to be the same kind of phenomenon.
Question 2
Ontological reduction is the claim that one phenomenon is in fact the same type or kind of phenomenon as another.
Applied to identity theory:
types of mental state are identical to types of brain state.
What is true of mental states and their properties is therefore reducible to what is true of physical brain states and their properties.
Question 3
Identity theory is ontologically reductive because it claims that mental-state types and brain-state types are actually the same kinds of phenomena.
However, it is not analytically reductive.
The language used to refer to a mental state does not have to mean the same thing as the language used to refer to the relevant brain state.
Therefore:
mental-state type = brain-state type
may be ontologically true even though the terms "mental state" and "brain state" are not synonymous.
Question 4
One possible answer is to apply Descartes' indivisibility argument.
Descartes argues that minds and bodies have different essential characteristics: bodies are divisible while minds are not divisible in the relevant sense.
If this argument succeeds, mental reality cannot be identical to physical bodily reality.
Since brain states are physical states, a mental-state type could not then simply be identical to a brain-state type.
Alternatively, students could apply the conceivability argument, Chalmers' philosophical-zombie argument or Jackson's Knowledge/Mary argument, provided the argument is accurately explained and connected to the proposed physical reduction.
Question 5
The multiple-realisation objection claims that the same mental state can be instantiated by different physical processes.
Mind-brain type identity theory claims that a mental-state type is identical to a brain-state type.
But if the same mental-state type can be realised by physically different processes, it cannot straightforwardly be identical with one particular physical type.
Multiple realisation therefore challenges the type identities required by the theory.
Question 6
Type identity theory requires a correspondence of the form:
mental-state type M = physical-state type P
If the claim in the question is correct, anything genuinely in mental state M should therefore instantiate physical type P.
The multiple-realisation objection claims that the same mental-state type can instead be instantiated by different physical processes.
So M might be realised through P in one case but through a different physical process in another.
If these are genuinely different physical types while the mental-state type remains the same, M cannot simply be identical to P.
The objection therefore attacks the one-to-one type identity required by the theory.
Question 7
Both philosophical behaviourism and mind-brain type identity theory are reductive physicalist approaches, but they reduce mentality in different senses.
Philosophical behaviourism concerns analytical reduction. Hempel claims that mental-state propositions can be reduced without loss of meaning to physical-language propositions about bodily states or movements. Ryle analyses mental-state propositions through behavioural dispositions.
Mind-brain type identity theory instead makes an ontological reduction. Types of mental state are claimed to be identical to types of brain state.
The theory does not require the terms used for mental and brain states to mean the same thing.
Therefore:
Behaviourism reduces mental-state language.
Identity theory reduces the mental phenomena themselves to physical brain phenomena.
They also face different objections. Behaviourism faces Super-Spartans, perfect actors, circularity, behavioural multiple realisability and asymmetry. Identity theory faces dualist arguments and the multiple realisation of mental states through different physical processes.
Question 8
A successful 25-mark response should explain the theory precisely and evaluate the specified objections.
Relevant material includes:
physicalism
brain states as physiological states or processes
mental-state types
brain-state types
the claim of type identity
the distinction between identity and causation
ontological reduction
analytical reduction
why the theory is ontologically but not analytically reductive
comparison with philosophical behaviourism
dualist arguments applied to identity theory
Descartes' indivisibility argument
Descartes' conceivability argument
relevant property-dualist arguments, including philosophical zombies and Knowledge/Mary
the physicalist responses already considered to those dualist arguments
multiple realisation
the claim that one mental-state type can be instantiated by different physical processes
why this challenges one-to-one type identities
the distinction between behavioural and physical multiple realisability
the fact that rejecting type identity theory does not automatically establish dualism
the possibility of alternative physicalist theories
a reasoned judgement about whether type identities can adequately account for the range of mental states
A strong evaluation will focus particularly on the theory's distinctive claim about types. Identity theory is stronger than the claim that mental states simply depend upon brain states. It says that the mental-state type is the brain-state type. Dualist arguments challenge the proposed physical reduction, while multiple realisation challenges whether a single physical type can be identified with a mental type at all.
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