The Conceivability Argument

An attempt, through reasoned argument, to show that the claim that the mind and brain are identical is false

To understand the arguments an understanding of the different kinds of possibility and impossibility required

What do we mean when we say “It is impossible for a human being to run a mile in two minutes or to jump fifty feet?”

It is beyond the capabilities of human due to their physiology and the laws of physics. Such things are impossible given the way the world works - they are physically impossible

These suggestions (that humans can run a mile in two minutes or jump fifty feet) are not impossible in the same way in which it is impossible for a square to be circular, or 2 + 2 to equal 5

They are different kinds of impossible - how are they different?

A human able to run a two minute mile or jump fifty feet are physically impossibilities in the real world.

However, even though we know that these things are impossible in the real world, we can give a coherent description (that involves no contradiction) of how these things might be possible if human physiology or laws of physics were different

Such things might be possible if humans had a greater lung capacity or larger muscles.

We can give a description of a state of affairs that though physically impossible (because it is not allowed by the laws of nature obtaining to our world) is metaphysically possible - allowed by the laws in some other possible world

We can do no such thing where circular squares are concerned

A circular square or 2 + 2 = 5 would be impossible no matter how different the world might have been. They are not just physically impossible, they are metaphysically impossible

Metaphysically impossible - they are impossible not only in the actual, but in any possible world

A world with circular squares cannot be coherently described; any attempt to describe it involves a contradiction so there can be no such world

The principle of conceivability entails metaphysical possibility. How does this principle help Descartes show that the mind and brain are separate things?

If we claim that the mind and the brain are identical then we are claiming that it is metaphysically (and physically) impossible to have minds without brain

If we claim that the mind and brain are identical then we are claiming that it is metaphysically (and physically) impossible to have mind without brain

If Mind = Brain it should be impossible to give a coherent description of a world where mind exists without brain: mind existing without brain should be inconceivable

Descarte believed that if it is metaphysically possible to have mind without brain, then mind and brain can’t really be identical after all

If it is conceivable for mind to exist apart from brain - if we can give a coherent description of mind existing apart from brain - then A and B aren’t identical

Presented inductively

• If the mind and the brain are the same, we should not be able to give a coherent description of a possible world in which the mind exists apart from the brain

• We can give a coherent description of a possible world in which the mind exists apart from the brain

• Therefore, the mind and the brain cannot be the same