Spiritually and generically religiously, “the soul” means “life force.” As in, its the thing that makes things alive. The native Americans, for example, felt everything had a “soul.” The rocks, the trees, the animals, the people, the sky. It would be the ‘spirit’ that makes that thing ‘real.’ Its also the part of that thing that appears in dreams. Dreaming is more or less how the idea of the soul came into being. How can you go somewhere when you’re asleep and see things like rocks and trees, yet still be in your bed? Your soul leaves your body and goes somewhere and sees the souls of rocks and trees, and maybe people already dead. To many cultures dreams were as real as real life. So, the soul and the souls of objects were also real.

In most of Christianity (generally speaking), “the soul” would be the spark of the divine in humans only that gives us life and free will. Without it we would not have the ability to choose and we would be like animals. It’s what allows you to get around the fact you’re a bundle of chemicals and are subject to physical deterministic effects. As in, it gives you the ability to override your instincts and objectively choose, free will. It’s also the part of you that takes your experiences and “self” up to heaven or down to hell when you die. Like a repository of all your thoughts and memories.

I would say, without this kind of soul, it’s hard to prove free will exists.

Scientifically, “the soul” would be the “spark of life” all living things have. Why can’t you get a dead body to start up again with the right chemicals or something? Because a living thing is so complex that once its harmony is disrupted it can’t be gotten back. That harmony would be the “soul.” Some living things are more complex than others, so there even harder to “get back.” Once the brain is damaged, the unique ordering of chemicals and electronically impulses that makes you “you” is gone. That would be the “soul” scientifically.

Here is the only study I know of that did anything on the soul, weight of the soul. Results were… inconclusive.

Here is the wiki on the subject. I wrote this post from my own flawed memory, so you might want to read the wiki as well:

http://en.wikipedia.org/wiki/Soul

Really, I’m talking about two kinds of ‘scientific soul.’ One being a “life force” the other being a “repository of thoughts and experiences.”

I’m saying that in some sense “brain dead” people have ‘lost’ the second kind of “scientific soul.” As in, the “person” that existed before the damage is gone.

People who are born with a “damaged brain” do have both kinds of souls. They have a personality and remember their past experiences and are, of course, alive. I did not mean to infer otherwise.

If a person gets damage done to their brain so that they now have a different personality, I would say, in some sense, they lost their “soul.” (or at least, their second kind of ‘scientific soul’ was replaced with another one)

But, for both kinds of “scientific souls” we are talking about an unique ordering of chemicals and electrical impulses. One ordering, which I called “harmony” above, keeps you alive. The other I am talking about is the ordering in the brain that gives you (or any animal really) memories and a personalty. For exampled, some dogs are mean and some dogs are nice.