The Cartesian Problem For Materialism Descartes proved, beyond the shadow of a doubt in my humble opinion, that the physical could be an illusion, unreal but, the mind, for certain, is not. Cartesian skepticism undermines materialism by showing the reality of the physical can be questioned but you couldn't doubt the existence of the mind. — TheMadFool
I'm afraid I have to doubt your certainty. Descartes showed that he had a brain, sure, but he has failed to show that the voice he could hear inside his head originated with him.
a thought experiment: you are lying on a beach. you can see the waves crashing on the shore. you can hear those waves crashing on the shore. in your mind you associate the sound you can hear with the waves you can see, so that it appears to you that the sound is created by the waves. this clearly shows that sounds inside your head can, or may, or possibly might sometimes, originate outside your head.
now close your eyes, and listen to the waves crashing on the shore. absent the visual signal, you are unable to tell whether the sound has an origin interior to or exterior to your head. there is simply no way to tell.
now explain how Descartes is able to prove, in your own words, "beyond the shadow of a doubt," that the voice he can hear is his?
I really don't have a problem if you want to claim that this is the most probable, the most likely, scenario, and that alternatives sound more like science fiction than philosophy. but to claim that Descartes "proved" this is simply not true.
Descartes showed that he had a signal processing organ inside his head that we call the brain. but you cannot prove where any of those signals originate.
Kaarlo Tuomi