Substance Dualism

Substance Dualism

The view that there are two fundamentally different types of substance: physical substances or bodies and mental substances, or minds.

Substance

Something that does not depend on another thing in order to exist, which possesses properties and persists through changes. 

Property

An attribute or characteristic of a substance. Depends on the substance in order to exist.  

Indivisibility Argument

• P1. It is a law of logic that if x and y have exactly the same properties then x=y  

• P2. If there is a property P that x has but that y does not have then x is not numerically identical to y.  

• P3. My body is always divisible.  

• P4. My mind is always indivisible.  

• C1. Therefore, my body cannot be the same substance as my mind.  

The mental is divisible in some sense

Modern neuroscience shows brain damage can impair parts of the mind, effectively dividing it. There is also split-brain surgery and multiple personality disorder which show a division of consciousness. 

Not everything thought of as physical is divisible

Things like elementary particles like atoms, or electromagnetic fields aren’t legitimately divisible, yet they’re physical. 

The conceivability argument

• P1. If I can clearly and distinctly recognise the nature of two things to be different then they are different   

• P2. I can conceive (clearly and distinctly recognise) that my mind, a thinking non-extended thing, can exist without my physical non-thinking extended body existing.   

• C1. Therefore it is metaphysically possible for my mind to exist without a body.   

• P3. If it is metaphysically possible that X exists without Y, then Xand Y are not identical.   

• C2. Therefore, my mind is not identical with my extended body.   

Mind without body is not conceivable

The separation of mind and body is only apparently conceivable, not genuinely. Clear and distinct conceivability requires full understanding, which we lack regarding the nature of the mind.

What is conceivable may not be metaphysically possible

Just because we can imagine something doesn’t mean it could really exist. One might conceive of a right-angled triangle without a hypotenuse but that’s impossible once we know Pythagoras' theorem. It was conceived before it was understood, therefore, conceivability doesn’t guarantee metaphysical possibility.

What is metaphysically possible tells us nothing about the actual world

Even if minds without bodies are metaphysically possible, that doesn’t prove they actually exist. It’s possible unicorns could exist, but that doesn’t mean they do.