Posted by alexandra_k on July 5, 2005, at 5:05:11
Descartes was an interactionist substance dualist. His main claims on the nature and relationship between mind and matter can be summarised as follows:
1) Mind is made of immaterial substance.
2) Matter (including body and brain) is made of material substance.
3) Mind interacts with matter and matter interacts with mind via the pineal body.So he believes that there are two distinct things or entities: mind, and matter.
He believes they are different kinds of stuff, or substance (immaterial and material respectively).
He believes that matter can cause changes to mind (as when you hit your thumb and feel pain).
He believes that mind can cause changes to matter (as when you decide to raise your arm and it raises into the air).
He was most probably wrong about the pineal body... But best not throw the baby out with the bath water just yet.Descartes arguments for dualism.
Leibniz law states that if we have x and y (at any one moment in time) and x has a property that y lacks then x and y cannot be the same thing.
So. Science tells us that water is one and the same thing as H2O (roughly...)
And now it seems that science tells us that mind is one and the same thing as brain (roughly...)
But if we can find one property that x (mind) has that y (body) lacks or vice versa then the scientific claim is necessarily false.
Descartes round one:
Mind has the property of indubitibility
Matter has the property of dubitibility
________________________________________
Mind has a property that matter lacks
________________________________________
By Leibniz law mind cannot be one and the same thing as matter.Interesting...
Here is a paralell argument (of the same structure)
Louis Lane wants to marry Superman
Louis Lane does not want to marry Clarke Kent
____________________________________________
Superman has a property that Clarke Kent lacks
____________________________________________
By Leibniz law Superman cannot be the same person as Clarke Kent.There are other problems with this example (to do with personal identity and identity of alternative states etc etc) but the relevant problem that this example is supposed to draw out is the kind of property that it is and is not appropriate to use in Leibniz law.
Leibniz law only works if we are making reference to genuine properties of the objects (x and y). It doesn't work for psychological properties. Basically, whether Louis Lane wants to marry Clarke Kent or not is a fact about Louis - not a fact about Superman or Clarke Kent (the x and y). Whether something is dubitable or indubitable (whether I am able to doubt something or not) is likewise a fact about me - not really a fact about mind and brain.
Descartes round two:
Mind is not extended in space
Matter is extended in space
______________________________
Mind and matter have different properties
_____________________________
By Leibniz law mind and matter cannot be the same thing.This one is trickier...
The materialist has to say that despite seeming counter-intuitive mind must be extended in space after all (because if the mind just is the brain then it turns out that the mind is located wherever the brain is located). Hmm.Being charitable to Descartes...
My pain is in my foot
My brain state is in my head
______________________________
My pain has a different location to my brain state
______________________________________________
By Leibniz law my pain cannot be my brain stateThe materialist has to say that despite it sounding rather counter-intuitive, your pain isn't in your foot after all. Your pain is in your brain. It is just that the brain state 'tells' you or 'tags' or 'projects' the location of the pain for you. Like how you don't see 2d images on the back of your retina - your brain projects 3d objects in the world
It does seem a little odd to deny those premises - but this is what the materialist needs to do. If mental states just are states of ones brain then the materialist cannot admit that the mental state has a property that the brain state lacks without contradiction.
How about this:
The morning star appears in the sky in the morning
The evening star appears in the sky in the evening
_________________________________________________
The morning star has a property that the evening star lacks
________________________________________________
By Leibniz law the morning star cannot be the evening star.(FYI the morning star and the evening star are typically thought to refer to venus. Philosophers like this one.)
Turns out we were mistaken with the premises - we were making a false claim about what we observe. It can be hard to find genuine properties of objects...
What about this?
Alexander the Great knew there was water in front of him
Alexander the Great did not know there was H2O in front of him (hadn't been discovered yet)...Same saga: properties of alexander and not of water / H2O.
lets be kind to Descartes round three:
I am imagining a yellow cow
My mental state has the property of being yellow
My brain state does not have the property of being yellow
_______________________________________
My mental state has a property my brain state lacks
_______________________________________
By Leibniz law my mental state cannot be my brain state.Hmm.
What would / could / should the materialist say about now??????
Methinks... They need to do some fast talking...
They have to deny either the first or the second premise.
I'd suggest the second. My brain state has to have the property of being yellow after all... But if you cut off the top of my head my brain won't look yellow to you...
poster:alexandra_k
thread:523626
URL: http://www.dr-bob.org/babble/write/20050621/msgs/523626.html