the theory that the origin and phenomena of life are dependent on a force or principle distinct from purely chemical or physical forces.
Within the universe I wish to create this is somewhat accurate. The bodies of creatures endowed with will (most animals, humans, etc..) are animated by a soul.
If the soul is removed from the body (through the use of magic) the creature in question will die.
I do not mean they will become soulless husks that are still technically alive like in the potterverse. I mean they become braindead and all their vital functions stop.
A bit more information about the soul:
The soul is not simply equivalent to consciousness. Though it does encompass what we call consciousness it is further more a physical field flowing within the body.
The soul permits certain complex mental processes such as self-awareness, sentience, self-introspection and imagination. In a more discrete way, it also increases (but is not necessary for) the effectiveness of memory, planning and reasoning compared to soulless objects such as computers.
The soul is essentially a secondary processing/memory storage unit in the context of the brain. So if you exchanged the souls of two people they'd go insane since the memories/personality traits stored in their brains and the memories/personality traits stored within their new souls would be "incompatible" and contradictory.
The soul can be extended outside the body to affect the area around it (moving objects, lighting fires, etc...). This process is called magic.
The soul is naturally attracted to the underworld/the afterlife/the spriritual realm/whatever you want to call it. A soul that is not within a body will make its way towards this place.
When within a body, the soul is deluded/preoccupied by basic desires like food, sex, sleep and avoiding danger. Because of this, when within a viable host body (one that desires these things) the soul will remain in it.
When a body is sufficiently damaged (braindead) the soul regains it's natural attraction to hell/heaven/nirvana/whatever you want to call it and goes there.
The soul, though nonmaterial, is definitely physical: it can be measured, collected, tested. It obeys the physical laws of my universe. It is not supernatural.
Now as you can see, I've explained why the soul leaves the body when the latter dies: the soul has no reason to stay and so it leaves. Simple.
However I can not see a way to explain sensibly why forcefully removing the soul would cause the body to die. Afterall:
The heart pumps because it is electrically stimulated by firing neurons.
Those neurons fire because they are provided with various sets of chemicals.
Those chemicals are provided to those neurons by the bloodstream.
The bloodstream is maintained by the heart.
And so on...
So why would the body suddenly cease to function if the soul, something seemingly completely unnecessary to the body's well-being according to our current medical knowledge, were to leave it?
Note: I am not looking for questions that simply say things like: "In your universe neurons won't fire unless the soul makes them." We know factually that this is not the case.