Constantine

I can hear the arguments already and I agree.  Demonic entities aren’t really the same thing as ghosts, but they get connected at times.  This could be why certain ghost categories get moved to demons depending on your definition.  So, how are they the same and different?

1. A big difference is that demons are sentient beings from another world with an evil goal in mind.  They are either from Hell to do Satan’s bidding or summoned from a void or anything else that makes them non-Earth.  Ghosts are spirits of the dead or created by trauma, so their origins are Earth.
2. There are some beliefs that demons were once humans, which does mean they are related to ghosts in some fashion.  Some even have them once being the ghosts of people who became corrupted by evil or dark emotions.  In this case, a demon would be an intelligent ghost that has lost its humanity and is now out to cause pain, suffering, and destruction.
3. Stories have both ghosts and demons possessing humans for their own reasons.  A demon would be to continue their evil agenda while a ghost might be doing it to relay a message or find peace.  This shared ability does mean that demons aren’t always corporeal or they at least have the ability to change to a spiritual form.  I have even found a few tales where ghosts and demons possess each other, but those are rare and not consistent.
4. While ghosts aren’t always aware of their situations, demons are and they have a more active influence on their surroundings.  Of course, you have wraiths, revenants, and other ghosts that have their awareness and can interact.  So, this isn’t a solid difference between the two.
5. Ghosts are typically linked to a place or person.  Demons are able to roam freely unless specifically contained somehow.  Usually, the containment of a demon involves magic or some kind of relic.  Yet, if a demon did come from a ghost who became corrupted, it would probably still be stuck in its location.  This is where we get conflicting information on the differences.

That’s really it, which makes it fairly straightforward on them being different.  At least, to most people it would look that way.  Going with the ‘demons are corrupted ghosts’ theory, you end up created a solid connection.  This one probably should boil down to personal beliefs.