Because the difference between the physical and the non-physical is far greater than the difference between shields and spears.
Nobody possesses a "differencometer" which can tell which differences are surmountable in the emergence of new properties and which are not. More importantly, you apparently do not believe this is an unbridgeable difference at all! (See the end of this post.)
If you have evidence how such a thing can occur, I am all ears.
The fact that changes to the physical brain cause changes to the mind is evidence that physical events cause mental events. (Your denial of this below does not stand up.)
[ME}: First, you're flatly refusing to answer my question, which was: do you, or do you not agree that 1) "it is impossible for reasoning to emerge from chemistry" and 2) "if it is not impossible, if reasoning actually does emerge from chemistry, then all reasoning is unreliable" are two different claims? I have no idea whether or not you recognize that they are in fact different claims.
See above about why it is probably impossible.
You are still flatly refusing to answer my question! I didn't ask whether "it" was possible or impossible, for any value of "it." I asked whether these were two different claims or not. Why is it impossible for you to say?
But if naturalism was true then your conclusions would be based on the ratio of chemicals in your brain, not based on logical reasoning based on premises and weighing of evidence.
I've addressed this claim again and again and you simply make no effort to show why my counter-arguments are wrong: you just repeat and repeat the claim. Tell me, please,
which of the following premises you dispute.
1. If naturalism is true, then chemical reactions cause logical reasoning based on premises and weighing of evidence.
2. If it is true that chemical reactions cause logical reasoning based on premises and weighing of evidence, then it must be true that logical reasoning based on premises and weighing of evidence is real.
3. If logical evidence based on premises and weighing of evidence is real, then logical evidence based on premises and weighing of evidence can be the real cause of our conclusions.
Therefore, if naturalism is true, then logical evidence based on premises and weighing of evidence can be the real cause of our conclusions.
If you can't dispute any of the premises, and you can't dispute the logic, you can't dispute the conclusion, and the conclusion is that your claim -- that if naturalism is true, our conclusions are not caused by logical reasoning and weighing of evidence -- is false.
And again, "but how can chemical reactions cause logical reasoning?"
is NOT a legitimate objection to claim 1. Claim 1 is a claim about what naturalism is asserting,
not about what is the truth of that assertion. It can be true that "naturalism asserts X," even if naturalism is
wrong to assert X.
No, none of that refutes the fact that it could be that the mind uses the brain to interact with the outside world so, if the brain is damaged it appears as if the mind is damaged but in fact it is not because it is not totally based on the physical brain.
People who have damage to a particular area of the brain lose the ability to acquire short-term memories (Korsakoff Syndrome). You are asserting that the mind is
not damaged when this happens, which is absurd.
The mind causes certain neurons to fire and you experience the various mental states.
And with that, you have entirely abandoned your own thesis.
First, if the mind is the cause of neuron firings, then something non-physical is the cause of something physical. But you were asserting, just now, that these two things are too different for one to cause the other! That was your
only argument for saying naturalism could not be true.
Secondly, either you are saying that neurons firing is the cause of the mental states -- in which case you are explicitly agreeing that physical events can cause mental events, and your thesis is fully out the window -- or you are saying that the mind causes the neuron firings, but those neuron firings do... what, exactly? You can say "interact with the outside world," but that's basically a meaningless phrase unless you can say specifically what you think they accomplish, what they cause.