Substance dualism
Substance dualism claims that both minds and bodies exist
The mind is an ontologically distinct substance
There are two types of substance: physical and mental
Cartesian dualism claims that minds do not depend on bodies to exist
If mental substances exist, they are unlike physical substances
Descartes’s conceivability argument
Meditation VI
P1 I have clear and distinct idea of myself something that thinks and is
not extended
P2 I have clear and distinct idea of body as something that does not
think and is extended
P3 If I have clear and distinct thought of something, God can create it
in a way that corresponds to my thought (Meditation VI)
C1 Therefore, God can create mind as something that is extended and
does not think
C2 Therefore, mind and body can exist independently of one another
C3 Therefore, mind and body are two distinct substances
Simpler form:
P1 It is conceivable that mind can exist without body
C1 Therefore, it is possible that mind can exist without body
C2 Therefore, mind and body are distinct substances
Mind without body is not conceivable
First inference: Descartes infers possibility from conceivability (C1)
Second inference: Descartes infers substance dualism from the
possibility that mind can exist without body (C2)
Challenging P1: can we conceive of mind existing without bodies clearly
and distinctly? As separate substances?
Descartes assumes he can identify what it is to think from introspection
He may think that it is conceivable that mind and body are distinct
substances when it is not
Behaviourism: mental states should be analysed in terms of behaviour,
and without behaviour, there is no mind
If correct, once we have understood what we mean by mind, we will
realise mind without body is inconceivable
Response: If behaviourism correct, disembodied minds (God) are
inconceivable, and for history of humanity, people claim to make sense of
these ideas
It is likely that behaviourism is wrong to think that in talking of mental
states we talk about behaviour, so mind without body is conceivable
To object to P1, need to argue either:
, 1. We cannot clearly and distinctly conceive of the mind as separate
from the body
2. Challenge Descartes’s theory of clear and distinct ideas
guaranteeing truth
What is conceivable may not be metaphysically possible
Challenging first inference made by Descartes
Suppose we can conceive of minds and bodies as distinct substances
Just because we can does not mean our minds and bodies could be
distinct substances
Maybe, to exist at all, minds depend on bodies
What is metaphysically possible is constrained by real nature/identity of
things
Something can be conceivable but not metaphysically possible (thinking
water is something distinct, not H2O)
Descartes needs to show that this above theory of mind is false
Needs to show that mind is substance, not just a way of talking about
mental properties
Then he can use indivisibility argument to show it is not a physical
substance
Descartes’s indivisibility argument + Leibniz
Mind and body’s different essential properties – thought and extension
(discussed in Meditation II)
Thought is understood in terms of consciousness and intentionality
Extension is property having size, taking up space
Mind and body therefore cannot be the same thing (Meditation VI)
If they were the same thing, they would have the same properties
Leibniz’s principle of indiscernibility of identicals: if two things are
identical (are just one thing), they share all their properties
One thing cannot have different properties from itself
Why think that the mind has different properties from the body?
Descartes: mind does not have any parts, unlike physical objects, and
cannot be divided, so it is not extended
The mental is divisible in some sense
Mental illnesses (multiple personality syndrome) used to suggest that
mind can be divided
In such cases, some parts of person’s mind is unable to communicate with
other parts
Theories of the unconscious
,People may believe/desire one thing consciously and the opposite thing
unconsciously
Talking about parts of a mind is possible
Response (Descartes): the way in which the mind is divisible is different
to the way in which the body is
Bodies are spatially divisible; minds are functionally divisible (different
parts do different things but are not in different spatial locations)
Not everything thought of as physical is divisible
Is it true that physical substances are always divisible? Infinitely so?
The smallest particle cannot be divided spatially
There are some physical indivisible things, so divisibility is not an essential
or defining property of every physical thing
So the fact that the mind is not divisible does not mean it is not physical
Could be non-divisible physical thing
Response: maybe not in reality, but can conceive of this smallest particle
having half the size
So we can still talk about spatial parts
Indivisibility argument assumes that minds exist as substances,
then argues they are not physical substances
Suppose minds are not things or substances at all
Then minds are not divisible or indivisible, they just do not exist
Instead, there are only mental properties (thoughts, desires, pains) –
perhaps they are properties of the brain
These properties are not spatially divisible but properties in general are
not divisible
Only substances literally have parts
Properties themselves do not take up space in way physical substances
do, so they cannot be divided into spatial parts
A substance that is spatially divisible can nevertheless possess properties
that are not divisible
What we think is distinct may not always be distinct
Masked Man instance – I conceive that the masked man is not my father
I can conceive that my father is not the masked man (it is logically
possible) but this does not show that it is metaphysically possible that my
father is not the masked man
From my conceiving that two people are distinct, we cannot infer that it is
metaphysically possible that they are distinct
Response: it is a mistake to try to understand mind’s power to act on
physical objects in terms of how physical objects act on each other
How would physical objects cause changes in mind?
, Impossible to exert physical force on mental substance with no spatial
location
Empirical interaction problems against interactionist substance dualism
Focus on incompatibility between interactionist dualism and empirical
science
First empirical problem: law of conservation of energy states in any
closed system total energy remains unchanged
In premise form:
P1 If mind (non-physical substance) moved body, total energy in
universe would increase
P2 If total energy increased, law of conservation of energy would not
apply to universe and universe not a closed system
C1 Therefore, if mind moved body, law of conservation of energy would
not apply to universe and universe is not closed system
C2 Therefore, because mind is not physical, physics cannot give us
complete account of energy in universe, as mind changes energy in
universe
Response to problem: physics is wrong to think that physical movement
can only be caused by physical force
Second empirical problem: if mind moves body, it does so by changing
what happens in the brain, as movements of body are caused by physical
events in brain
If interactionist dualism true, neuroscience must discover that some vents
in brain have no physical cause and are caused by mind
Applied to Descartes’s conceivability argument: Descartes argues
that it is possible for the mind to exist independently of the body because
he can conceive of it existing without the body
Because it is logically possible for the mind to exist without the body, it is
also metaphysically possible
But this does not follow
Maybe, unknown to him, the mind is not an ontologically independent
substance, and it is metaphysically impossible for it to exist separately
from the body
Response: we cannot, in general, infer what is metaphysically possible
from what we think, but in case of clear and distinct ideas, inference is
justified
Because he can clearly and distinctly conceive that mind and body are
distinct substances, it follows that it is possible that they are
Substance dualism claims that both minds and bodies exist
The mind is an ontologically distinct substance
There are two types of substance: physical and mental
Cartesian dualism claims that minds do not depend on bodies to exist
If mental substances exist, they are unlike physical substances
Descartes’s conceivability argument
Meditation VI
P1 I have clear and distinct idea of myself something that thinks and is
not extended
P2 I have clear and distinct idea of body as something that does not
think and is extended
P3 If I have clear and distinct thought of something, God can create it
in a way that corresponds to my thought (Meditation VI)
C1 Therefore, God can create mind as something that is extended and
does not think
C2 Therefore, mind and body can exist independently of one another
C3 Therefore, mind and body are two distinct substances
Simpler form:
P1 It is conceivable that mind can exist without body
C1 Therefore, it is possible that mind can exist without body
C2 Therefore, mind and body are distinct substances
Mind without body is not conceivable
First inference: Descartes infers possibility from conceivability (C1)
Second inference: Descartes infers substance dualism from the
possibility that mind can exist without body (C2)
Challenging P1: can we conceive of mind existing without bodies clearly
and distinctly? As separate substances?
Descartes assumes he can identify what it is to think from introspection
He may think that it is conceivable that mind and body are distinct
substances when it is not
Behaviourism: mental states should be analysed in terms of behaviour,
and without behaviour, there is no mind
If correct, once we have understood what we mean by mind, we will
realise mind without body is inconceivable
Response: If behaviourism correct, disembodied minds (God) are
inconceivable, and for history of humanity, people claim to make sense of
these ideas
It is likely that behaviourism is wrong to think that in talking of mental
states we talk about behaviour, so mind without body is conceivable
To object to P1, need to argue either:
, 1. We cannot clearly and distinctly conceive of the mind as separate
from the body
2. Challenge Descartes’s theory of clear and distinct ideas
guaranteeing truth
What is conceivable may not be metaphysically possible
Challenging first inference made by Descartes
Suppose we can conceive of minds and bodies as distinct substances
Just because we can does not mean our minds and bodies could be
distinct substances
Maybe, to exist at all, minds depend on bodies
What is metaphysically possible is constrained by real nature/identity of
things
Something can be conceivable but not metaphysically possible (thinking
water is something distinct, not H2O)
Descartes needs to show that this above theory of mind is false
Needs to show that mind is substance, not just a way of talking about
mental properties
Then he can use indivisibility argument to show it is not a physical
substance
Descartes’s indivisibility argument + Leibniz
Mind and body’s different essential properties – thought and extension
(discussed in Meditation II)
Thought is understood in terms of consciousness and intentionality
Extension is property having size, taking up space
Mind and body therefore cannot be the same thing (Meditation VI)
If they were the same thing, they would have the same properties
Leibniz’s principle of indiscernibility of identicals: if two things are
identical (are just one thing), they share all their properties
One thing cannot have different properties from itself
Why think that the mind has different properties from the body?
Descartes: mind does not have any parts, unlike physical objects, and
cannot be divided, so it is not extended
The mental is divisible in some sense
Mental illnesses (multiple personality syndrome) used to suggest that
mind can be divided
In such cases, some parts of person’s mind is unable to communicate with
other parts
Theories of the unconscious
,People may believe/desire one thing consciously and the opposite thing
unconsciously
Talking about parts of a mind is possible
Response (Descartes): the way in which the mind is divisible is different
to the way in which the body is
Bodies are spatially divisible; minds are functionally divisible (different
parts do different things but are not in different spatial locations)
Not everything thought of as physical is divisible
Is it true that physical substances are always divisible? Infinitely so?
The smallest particle cannot be divided spatially
There are some physical indivisible things, so divisibility is not an essential
or defining property of every physical thing
So the fact that the mind is not divisible does not mean it is not physical
Could be non-divisible physical thing
Response: maybe not in reality, but can conceive of this smallest particle
having half the size
So we can still talk about spatial parts
Indivisibility argument assumes that minds exist as substances,
then argues they are not physical substances
Suppose minds are not things or substances at all
Then minds are not divisible or indivisible, they just do not exist
Instead, there are only mental properties (thoughts, desires, pains) –
perhaps they are properties of the brain
These properties are not spatially divisible but properties in general are
not divisible
Only substances literally have parts
Properties themselves do not take up space in way physical substances
do, so they cannot be divided into spatial parts
A substance that is spatially divisible can nevertheless possess properties
that are not divisible
What we think is distinct may not always be distinct
Masked Man instance – I conceive that the masked man is not my father
I can conceive that my father is not the masked man (it is logically
possible) but this does not show that it is metaphysically possible that my
father is not the masked man
From my conceiving that two people are distinct, we cannot infer that it is
metaphysically possible that they are distinct
Response: it is a mistake to try to understand mind’s power to act on
physical objects in terms of how physical objects act on each other
How would physical objects cause changes in mind?
, Impossible to exert physical force on mental substance with no spatial
location
Empirical interaction problems against interactionist substance dualism
Focus on incompatibility between interactionist dualism and empirical
science
First empirical problem: law of conservation of energy states in any
closed system total energy remains unchanged
In premise form:
P1 If mind (non-physical substance) moved body, total energy in
universe would increase
P2 If total energy increased, law of conservation of energy would not
apply to universe and universe not a closed system
C1 Therefore, if mind moved body, law of conservation of energy would
not apply to universe and universe is not closed system
C2 Therefore, because mind is not physical, physics cannot give us
complete account of energy in universe, as mind changes energy in
universe
Response to problem: physics is wrong to think that physical movement
can only be caused by physical force
Second empirical problem: if mind moves body, it does so by changing
what happens in the brain, as movements of body are caused by physical
events in brain
If interactionist dualism true, neuroscience must discover that some vents
in brain have no physical cause and are caused by mind
Applied to Descartes’s conceivability argument: Descartes argues
that it is possible for the mind to exist independently of the body because
he can conceive of it existing without the body
Because it is logically possible for the mind to exist without the body, it is
also metaphysically possible
But this does not follow
Maybe, unknown to him, the mind is not an ontologically independent
substance, and it is metaphysically impossible for it to exist separately
from the body
Response: we cannot, in general, infer what is metaphysically possible
from what we think, but in case of clear and distinct ideas, inference is
justified
Because he can clearly and distinctly conceive that mind and body are
distinct substances, it follows that it is possible that they are
