Materialists believe that "mind" is merely a word we use to describe the functioning of the human brain. It's what the brain does. The mind is to the brain like digestion is to the stomach. Just as there's no organ or immaterial substance in us called "digestion" so, too, there's no immaterial substance called mind.
Dualists believe that, there is something about us that's immaterial and which works in concert with the body (brain) in order to produce the phenomena of our conscious experience.
The debate is important because what one believes about this "mind/body" problem affects much else that one believes.
For example, if one is a materialist it's much harder to maintain a belief in free will (and thus moral responsibility), life after death (since there's nothing to survive the death of the body), personal continuity of the self (since if we're only material substance and that substance is in constant flux, what is it that makes us the same self over time?), or God (since God is an immaterial mind).
If one is a dualist of one sort or another, it's much easier to accommodate each of these in one's overall belief system.
Here are just three of the materialist claims presented in the Mind Matters article along with brief responses to each.
Claim: The mind just emerged, slowly over eons, from the brain.Read the rest at Mind Matters where you'll also find links to support each of the assertions made above.
Response: The mind cannot just “emerge from” the brain if the two have no qualities in common — the one is immaterial, the other material.
Claim: Brain damage shows that the mind is really just the brain. Damage the brain and the mind goes … poof!
Response: That might be a good argument if things always happened that way. But a common treatment for severe epilepsy is to split the brain in half. The patient usually suffers only minor disabilities. Some people think and speak with only half a brain.
Modern neuroscience is also shedding light on the minds of people in a persistent vegetative state (PVS). The preferred new term is “disorders of consciousness.”
For example, in one study, “Remarkably, five patients were able to willfully modulate their brain activity, suggesting that, though unable to express any outward signs of consciousness at the bedside, they could understand and follow the researchers’ instructions.”
Generally speaking, people in a coma can hear and understand us.
Brain damage is a serious business, but it hardly shows that the mind is not real. Modern neuroscience enables us to identify many instances of humans struggling to express themselves using the available resources. That’s sometimes called neuroplasticity.
Claim: Don’t most professional neuroscientists say that the mind is just the brain?
Response: Many scientists believe that, not because of evidence, but because they are materialists. Thinking it through carefully, the idea doesn’t even make sense, as neurosurgeon Michael Egnor points out: “How do we believe that there are no beliefs?
If eliminative materialism (a form of materialism that claims that conscious experience is an illusion) is true, then their own belief in eliminative materialism isn’t a belief. It’s a physical state, a certain concentration of neurochemicals that we (the uninitiated) foolishly call a belief. In fact, the mind’s reality is consistent with neuroscience.
It’s not popular with many neuroscientists but that's (because of philosophical or theological reasons, not scientific reasons).