In the philosophy of mind
substance dualism is the view that there are two kinds of substance
physical or material substance
and the non-physical or immaterial substance of souls, minds or consciousness.
It contrasts with monist theories and their requirement of only one fundamental substance.
Although other theories use the term 'dualism', they won't be the focus here
so for convenience, 'substance dualism' will be referred to as 'dualism'.
Something that instantly triggers our scepticism of this philosophy
is the use of the term 'non-physical substance'.
What exactly is this supposed to mean?
Let's be clear: concepts like truth and justice may be defined as 'abstract' ideas.
In that sense, it's reasonable to call them non-physical concepts.
But they don't have their own independently active existence.
What dualists are proposing is a non- physical thing existing in addition
to brains and physical matter, as an active, thinking entity.
Clearly, they must explain in what sense a thing that thinks can be non-physical.
Some dualists see this 'non-physical substance' as a kind of 'stuff'
that lies beyond science, like ectoplasm, a supernatural substance
claimed to issue from 'ghosts' and 'spirit-channelers'.
Richard Swinburne talks of soul-stuff that comes in indivisible chunks.
But it's somewhat misleading to call this 'non-physical':
it clearly implies something with structure
a kind of physical stuff, albeit an abnormal one.
Dualists who claim this abnormal stuff exists
need to give evidence of its existence
explain which special property allows this stuff to think when brain stuff can't
and explain how it can be shown
that their proposed abnormal stuff possesses that property.
Alternatively, if dualists define their 'non-physical substance'
as a thing with no physical attributes whatsoever
there are much bigger problems.
How is a thing with no conceivable physical aspect meant to think?
Or do anything at all?
In what sense could it even be said to exist?
If minds are entirely non-physical, what anchors them to particular bodies?
These are not questions to be swept aside
nor do they reflect some irrational dread of dualism and its implications.
They reflect a reasonable expectation
that dualists who make the factual claim
that mind or consciousness is a non-physical substance
should make their claim comprehensible.
Dualists who can't or won't explain coherently what they're proposing
have no genuine complaint if dualism gets a poor reception.
Likening a non-physical substance to energy, magnetic fields
or sound waves channeled by a radio set is obviously a non-starter
as those things are all physical.
Saying a non-physical thing is like a physical thing except it’s not physical
glosses over the very thing that needs explaining.
Whether what's being proposed is a thinking thing with literally no physical existence
or a kind of 'stuff' declared to be beyond science
what's striking about dualism from the outset
is its reliance on a concept that defies investigation.
These videos examine a range of arguments commonly used
to try to justify the dualist's non-physical substance.
First a brief note on terms like 'soul', 'mind' and 'consciousness'.
These are often used interchangeably, but they have crucial differences.
Things we classify as 'operations of mind' aren't always conscious.
For instance, when we try to recall a piece of information
it may appear quite suddenly in our consciousness
- which concerns the contents of our awareness or experience -
without us ever being aware of the processes of mind that retrieved it.
When it comes to 'souls'
the concept of spirit essences that survive physical death
needs its own separate evidence
LONG before we throw it into the mix with minds and consciousness.
These terms are not interchangeable.
So, when using them, it should be remembered
that statements about one don't automatically apply to another.
Why do some claim there are two kinds of substance?
Dualists from René Descartes to John Eccles
have claimed that some human abilities
can't be embodied in physical systems.
But we don't know nearly enough to justify such claims.
If asked which abilities are needed to play chess
we might once have said "an ability to think".
But in developing machines that can now beat us at chess
we've found that processes behind playing chess are not endlessly mysterious
but definable in fairly straightforward terms.
The very task of building machines that simulate human abilities
is forcing us to identify and correct our misconceptions of the processes involved.
It requires both an under- standing of the principles
governing the abilities we want to simulate
and knowledge of how to apply that understanding to technology.
Descartes said no machine could arrange its speech
so as to reply appropriately to whatever is said in its presence.
Human ability in language currently surpasses that of machines in many respects
but that may be due to the way we've previously tried to build
such abilities into machines, by inputting words and syntactic rules.
John Macnamara has pointed out that what drives human language acquisition
is a child's need to understand and express itself.
Human language is more about using words to express ideas.
Andrew Lock notes that humans translate language
not merely by replacing the words and grammar of language A with those of language B
but by translating the ideas expressed in language A into language B.
Observations like these are often misinterpreted.
They're not intended to show an unbridgeable gap between humans and machines.
As Max Velmans points out
the aim is in fact to define the gap more accurately in order to cross it.
And artificial intelligence research
is exploring the development of machines that learn language
through interaction with the world, rather than having words and rules loaded in.
Increasingly sophisticated computers and state-of-the-art machines
can now do things our ancestors might well have thought impossible.
The humanoid robot Asimo can identify faces, speech and gestures;
use sign language;
navigate its environment, including stairs;
detect and avoid objects;
it can even hop, jump and run.
If we haven't yet simulated specific human abilities in machines
this is not evidence such machines can't be built in principle.
It may be evidence of nothing more
than the current limits of our understanding and technology.
As Steven Pinker notes:
"The ultimate attainments of artificial intelligence are unknown,
and will depend on countless practical vicissitudes
that will be discovered only as one goes along."
The claim that some human abilities can't be embodied in purely physical systems
is not only already being eroded by advances in technology;
it's also absurdly premature when we have such incomplete knowledge
of what physical systems are capable of.
Alvin Plantinga says a physical object "just isn't the sort of thing that can think"
that interaction between physical parts can't produce thought.
But he admits his argument depends on intuition
and that "maybe not everyone sees things the same way".
To those who don't share his intuition
he advises they "just think about it some more"
and he refers them to a claim by Gottfried Leibniz
that if we take a machine that can think and we examine its parts
we'd find nothing to explain how it does so.
According to Plantinga, what Leibniz is saying here
is that thinking cannot arise by physical interaction.
But we have just been told the machine itself can think
not that there's some other substance doing the thinking.
A machine that can think - even if we can't explain how it does so -
can't be used to support Plantinga's claim that machines cannot think.
That's just self-contradictory.
Intuition and thought experiments about machines that think
do not substantiate Plantinga's claim that physical thinking things are 'impossible'.
Swinburne tries to support his case for dualism
by asking us to imagine the following scenario:
You remove his brain and divide it in two
putting each half into an otherwise empty skull.
If that’s not enough to produce two conscious persons
you add bits to each brain from Swinburne's identical clone.
He asserts that once you start them operating
you have two living persons with conscious lives
but you don't know which is Swinburne.
He says it may be number 1, 2 or neither of them
and claims this shows that you could know everything
that has happened to every atom of what was previously his brain
and yet not know what has happened to him.
He concludes from this that being Swinburne
must involve something else as well as his body.
But this argument is fatally flawed, which we can easily show
if, instead of brains, we talk about car batteries.
Remove a battery from a car and divide it in two
putting each half into a car with no battery.
If each half isn't enough to power a car, add
bits to each battery from an identical car.
If we now ask, "Which is the original battery: number 1, 2 or neither of them?"
the trivial and obvious answer is that each new battery has parts of the original.
There's no grand mystery forcing us to say
that being the car must involve something as well as the physical car.
Swinburne's thought experiment tells us nothing more profound
than that if we divide the parts of one object to make two new objects
both new objects will have parts of the original.
It gives us no special insight into the nature of consciousness.
It's a red herring.
But it's even worse than that.
Let's re-examine Swinburne's wording:
he says that if the brain halves aren't enough to produce two conscious persons
we must add more bits of brain from his clone.
Unwittingly, Swinburne has told us
physical brain matter is sufficient to produce conscious persons.
Some dualists claim there are two kinds of substance
because of the private nature of our access to consciousness.
They argue that while you and I have public access to objects like paintings
you don't have access to my conscious experience, which is private to me
so consciousness must be a non-physical substance.
But why should you have access to my experience
if my experience arises from being this vastly complex and unique brain and body
- this changing configuration of matter - which is separate from you?
Dualists have objected that if we examine brains, we don't 'see thoughts'.
Plantinga complains that examining brains shows us nothing
that looks even vaguely relevant to semantic content.
But what exactly is Plantinga demanding we should see in the brain?
Visible chunks of meaning?
Many devices with far more limited functioning than brains
encode information in physical formats that don't reveal content.
If I film the sea with my digital camera
the camera creates a representation of the sea
but there's nothing resembling water among the circuits
and we don't propose non-physical entities to explain that.
Certainly, if thoughts had to possess the properties of what they represent
it would be an even bigger problem for dualism:
thoughts of water would have to be both made of water and non-physical.
Thoughts may not have 'weight, colour or texture' like physical objects
but then nor do processes like migration or metamorphosis.
So if thoughts and consciousness were representational processes
we wouldn't expect to describe them in the same way we describe objects.
It doesn't follow that things we don't describe like physical objects
must be non-physical objects.
No arguments mentioned so far give us any valid reason to embrace substance dualism.