Dualism
The reading for today is
Ch. 1 of Philosophy of
Mind: A Beginner’s Guide.
Substances and Properties
The properties of a thing are the ways that that
thing is, the features, characteristics, or qualities
of that thing.
Name Some Properties!
Substances and Properties
Substances (objects, individuals) are the things
that have (possess, instantiate) properties
(features, characteristics, qualities).
Substance Dualism
According to the substance dualist, there are
two kinds of substances: physical substances
and mental substances.
Physical Properties
Physical substances have physical properties:
• Size
• Shape
• Location
• Mass
• Charge
• Spin, etc.
Mental Properties
Mental substances have mental properties
[mental states]:
• Emotions
• Sensations
• Perceptions
• Thoughts
• Moods
Substance Dualism
The substance dualist thinks that no physical
substance has mental properties and no mental
substance has physical properties.
Minds don’t have size, shape, location, etc. and
brains don’t have moods, thoughts, pains, etc.
From the Reading
“[According to substance dualism] Your body is
like a probe, sent by NASA to explore a different
planet. The probe sends pictures back to mission
control, where scientists decide what the probe
should do next. Instructions are then sent back
to the probe which responds accordingly. The
probe itself is entirely unintelligent” (p. 10). And
it has no feelings, emotions, pains, etc.
ARGUMENTS FOR SUBSTANCE
DUALISM
Short Circuit
When I was 4 years old,
the movie Short Circuit
came out.
In it, a robot gets struck by
lightning and becomes
sentient.
Throughout the movie, various characters argue
that the robot can’t be sentient (have a mind),
because robots can’t _____:
Things with minds can _____
Robots can’t ______
Therefore, no robot has a mind.
Robots Can’t _____
•
•
•
•
•
•
•
Be expressive
Exhibit curiosity
Engage in playfulness
Speak fluidly
Learn new things
Appreciate beauty
Expect future conscious experiences
Robots Can’t _____
•
•
•
•
•
•
•
Have a fear of death
Act originally
Enjoy dancing and music
Have a sense of humor
Conform to moral laws out of principle
Mentally associate disparate things
Exhibit spontaneous emotional responses
Similar arguments can be made for substance
dualism. Instead of “Robots can’t _____,” the
substance dualist argues that there are things
minds can do that “No physical object can
_____”:
Minds can _____
No physical object can _____
Therefore, no physical object is a mind.
Is it possible for physical objects to do these
sorts of things– learn new things, be creative
and original, fear death, make plans for the
future, experience redness…?
Descartes
René Descartes (15961650) was a French
natural philosopher and
mathematician. He is the
father of modern
(Western) philosophy, and
he argued for substance
dualism.
The Cogito
Descartes famously said “I think, therefore I am”
(“Cogito ergo sum”).
He argued that it is not possible for him to
doubt his own existence. Only things that exist
can doubt.
The Deceiver
But Descartes thought it was possible for him to
doubt that he had a body.
Sure, it looks and feels like he has a body. But
couldn’t an all-powerful God make it seem like
Descartes had a body, when he really didn’t?
1.
2.
3.
4.
5.
I cannot doubt that I exist.
I can doubt that my body exists.
Therefore, I am not my body.
I am my mind.
Therefore, my mind is not my body
Leibniz
Gottfried Wilhelm Leibniz
(1646-1716), like
Descartes, was a natural
philosopher and
mathematician.
Among his many
achievements, he
formulated a law of logic
called Leibniz’s Law.
Leibniz’s Law
Also known as “the indiscernibility of identicals”
If X = Y, then X and Y have all the same
properties.
[Converse] If X and Y don’t have all the same
properties, then X ≠ Y.
Example
Property: being red
1. My car is red (has the property of being red.
2. That car is not red (does not have the
property)
3. Since my car and that car don’t have all the
same properties, that car is not my car.
Descartes’ Argument Again
Property: being a thing whose existence
Descartes can doubt.
1. Descartes’ body has the property of being a
thing whose existence Descartes can doubt.
2. Descartes does not have the property of
being a thing whose existence Descartes can
doubt.
3. Therefore, Descartes is not Descartes’ body.
The Masked Man Fallacy
1. I know that the masked man committed the
robbery– I was there and I saw him.
2. I don’t know whether my brother committed
the robbery.
3. Therefore, my brother did not commit the
robbery.
ARGUMENTS AGAINST SUBSTANCE
DUALISM
No Action at a Distance
At the time Descartes lived, it was commonly
believed that for one object to exert a force on
another, they had to contact one another.
But the mind, according to Descartes, is not
spatially located, has no surfaces, and no mass.
How can it contact and thus affect the body it
controls?
No Explanations
The substance dualist has not given us an
explanation for how the mind controls the body,
in the way that a physicist can tell us how the
mass of the various planets determine Earth’s
orbit.
We Can Already Explain Bodily
Movements
Why did I raise my hand?
Because a muscle in my arm contracted.
Why did the muscle contract?
Because of an electrical impulse in a nerve.
Why did the nerve have the impulse?
Because certain neurons in the brain fired.
Why did they fire?...
Substance Dualism Violates the Laws
of Physics
Physics says that the motions of particles are
completely determined by the physical forces
that act on them (the strong nuclear force, the
electro-weak force and gravity).
If a non-physical mind exerts a non-physical
force that changes the motion of ANY particle in
your body, then physics is wrong.
Unconscious Mental States
Philosophers used to think that all mental states
were conscious. If you thought that, then you
could say that consciousness is just part of being
in the non-physical mind.
But now we know there are unconscious mental
states. How can the substance dualist explain
what makes some mental states conscious and
others not?
Brain Damage
According to the substance dualist, mental
processes occur in the mind, and not in the
brain. (Many people like s.d. because it suggests
we can live on after the death of the body.)
Why then do damage to the brain or
degenerative brain diseases affect our ability to
think?
AVOIDING THE PROBLEMS
Property Dualism
Property dualism denies that there are any nonphysical substances.
Instead, it says that some physical substances, in
particular, brains, have mental properties in
addition to their physical properties.
Pros of Property Dualism
This can explain why brain damage, for instance,
can change your mental states or your ability to
have certain mental states.
Epiphenomenalism
Property dualism is often combined with
epiphenomenalism.
Epiphenomenalism says that brain events can
cause mental states, but mental states cannot
cause physical events.
Pros of Epiphenomenalism
The good thing about epiphenomenalism is that
it doesn’t contradict physics.
Since mental states can’t cause any physical
events, it’s true (as physics says) that the motion
of any particle is determined only by the
physical forces exerted on it.
Cons of Epiphenomenalism
The problem is that we have to deny two
seemingly obvious facts about mental states:
1. Some mental states cause action.
2. Some mental states cause other mental
states.
Abandon Dualism?
Why not just abandon dualism? Well, many have
done that.
BUT, some philosophers think there are very
good arguments for dualism. We will have
several classes on them later. In general, they
are arguments that conscious properties are not
physical properties.
SUMMARY
Substance Dualism
Substance dualism says that there are two kinds
of substances: physical substances with physical
properties and mental substances with mental
properties.
For Substance Dualism
Arguments for substance dualism assume that
physical things can’t have certain properties–
creativity, originality, consciousness, etc.
Since some things do have those properties, it
follows that the things that do are not physical
things.
Against Substance Dualism
The primary reason for rejecting substance
dualism is that it claims there are non-physical
causes of events– but we have never found any!
Second, it predicts that the mind should not be
affected by damage to the brain, but this is
obviously contradicted by experience.
Epiphenomenal Property Dualism
Property dualism combined with
epiphenomenalism can avoid these problems,
but only at the cost of denying that mental
states cause actions or other mental states.