I was thinking up a unique religion, and the religion was going to touch on humans being able to return to the here and now, at first they had a soul, but I found when I wrote about them coming back to talk to a loved one, I referred to them as a spirit. Is there a particular context, or environment that better suits one more than the other, or are they even all that different?
In common tounge we interchange mostly spirit ghost as opposed to soul and spirit. Religion likes soul more then spirit. Witchcraft likes spirit over soul. Meidiumship likes spirt over soul. And everyone shifts between ghost and spirit taking this more as the departed lexicon then that for the living.
We do already link demon and spirt together rather then demon and soul unless we speak of the person's own soul is a demon. Yet fairies, ghost, and spirit are also linked as well.
According to breif etymology:
Soul - is defined as a substantial entity believed to be in every person which lives, feels, thinks and wills. based off the Old Enligsh Sawol which to them meant the spiritual & emotional part of a person, inanimate or living being and it moves on from there.
Spirit - is the animating or vital principle in both man and animals, based on latin spiritus meaning more or less breathing of the gods. We get breathe of life from this concept.
Ghost - Is a supernatural immaterial creature, angel, demon, an apparition, a invisible corporeal being of airy nature. Stemming from only the mid to late 14th century.
There was a belief that light and sun where sperate things at one point.
To modern layman it's all the same soul, spirit, ghost it's incorporeal, you may or may not be able to interact with it (normally via mediums or your own senses), and it's considered airy or not wholly there (by non mediums) so as you can see it's linked up in our modern lexicon as similar enough.
You can make a religion if you wish that defines spirt and soul as separate. To them soul is housed in the body while spirit is free of fleshly confinement in human death or never had a body but was of a different composure we perceive as a similar to human spirit possibly helpful, possibly dangerous. Which if you differ to religion or witchcraft seems to be their take on it separate definitions for the state if it body house in life or not and devoid of it or outside of it all together like the laymen concept of demons are.
One thing to note witchcraft has the ethereal body/astral body still tied to the body of the living yet can become the new you should you wish for a time. Yet no one could confuse ethereal body for spirt, ghost, or soul language use wise.
Words, especially those which define entities which science has not yet categorized, are open to a wide range of interpretations. Just look at what the last twenty years of pop-fiction has done to Stoker's vampire.
So the real answer here is that these words mean whatever you choose to make them mean for your religion.
For your purpose, I would suggest that "soul" and "spirit" are related to each other in the same way as "body" and "corpse". The former describes the entity while it is being used by a living consciousness and the later, that same entity after death.
In this way, the sentence...
My soul was released during my death, becoming a spirit, free to roam though time and space without fetters.
The evil spirit poured itself into the coma patient, bound itself to that body's life force and thus became his new soul. From that stolen helm, the evil soul was able to bring his diabolical machinations back to the living world.
The words are totally open to interpretation, so I wouldn't worry too much about it. The possible interpretations are unbounded, but here are a few ideas that I've seen expressed in real life:
- Humans have souls, spirits are evil (or just foreign) entities.
- All life has a spirit. Souls are just stronger spirits that come from people.
- Souls are spirits that are still linked to bodies, once the body dies the soul becomes a spirit.
- Soul is just another word for Spirit.
- Souls are parts of humans, spirits are just myths.
There are more. Importantly for your situation, you're not limited to what real humans want to read into the words. You can define them for your world however you wish.
One thought I've had is that a spirit is a soul that has the ability to interact with the material world in some way. When a person (or a creature if you like) dies then their soul is freed to roam the ethereal world. For souls that have the ability to interact with the material world then when they choose to do so their manifestation in the 'real' world is a spirit. Whether they are just showing up for a chat with a descendant, to enact revenge on their enemies from beyond the grave or because they're just crazy enough to use whatever power they can get to lash out at the world, they do it as spirits. Perhaps the spirit is a construct inhabited by the soul in the same way that the soul used to inhabit a living form of flesh.
Another idea is that a soul is a compound entity and that some portion of it is supposed to ascend to a new phase of existence - a heaven, paradise or afterlife of some kind - but when it does so it leaves behind the rest of itself as a spirit. The spirit retains a copy of the memories, personality, etc. that the soul gained during life. Maybe the residual spirit degrades over time, maybe it simply loses interest, etc. Perhaps only souls with particularly strong life force or emotional connections leave such a residue behind.
I could come up with a number of other options, but this is your story so you should do it your way. There is no absolute authority that we have access to that can reasonably mandate one interpretation over any other, so it seems like you have free reign over how the people in your world view things.
Although maybe the people of your world are no more united on the definitions than we are.