You are assuming that there are no brain defects that could change your fundamental understanding of reality. This assumption would have to ignore clinical experience.
I understand there is a problem of measurement here: who decides who is sane and who is insane. But in this case the majority rules, even if there is no way to prove the majority is right.
Unrelated to the problem of demon possession, there is a famous case of an artist who lost his color vision due to a brain injury. It is possible, of course, for colorblind people to understand the concept of color, but this artist lost his memory of color and his ability to understand the concept of color. He was unable to imagine color in any way.
There are countless syndromes like this in which a brain deficit or injury results in the inability to understand or imagine what is lost.
If the true locus of consciousness is not the physical brain, then brain injuries should be perceived as a loss in the same way that loss of a limb is perceived. But this isn't the way it works. Brain disfunctions frequently "close," leaving the individual without the ability to perceive the loss.
I'm pleading ignorance here. Would you explain further?
But since we can't get inside other people's heads, it seems that we're up against the limits of our ability to know anything here with certainty.
Brain disfunctions frequently "close," leaving the individual without the ability to perceive the loss.
The ability of the mind to receive sensible forms depends on the proper functioning of the body's sense organs, so this would not contradict an essentially non-material theory of sense cognition.
"I understand there is a problem of measurement here: who decides who is sane and who is insane. But in this case the majority rules, even if there is no way to prove the majority is right."
Anybody else catch moral relativism out of that?