I'm not sure if this is answered in HOH:TL or Calebais as i don't own either of them, but can incantation of summoning the dead summon ANY dead persons ghost, assuming they haven't gone to heaven immediately (i.e. crusader, saint), haven't christian burial and you have the arcane connection.
My curiosity comes from the discussion in the necromantic spells thread about ghosts having either unfinished business or being confined to earth due to their deeds i life.
Given that the majority of folks DON'T come back as ghosts, does IOSD actually create a ghost from a normal dead person?
If so it bears interesting theological questions. Given that the soul of the person goes to purgatory or hell on death (crusaders/saints excluded) does this mean that the spirit resides on earth and is summoned by the magus from a "Dormant" state. Or does the spirit accompany the soul to purgatory/hell and the Magus summons it back to earth?
If the spirit remains on earth could it be seen (with appropriate magic) without IOSD in its dormant state?
Obviously the spell is useful for summoning know ghosts but it actually seems to create ghosts too. With access to a pagan burial area a wily magus could create an army of ghosts where none previously existed.
Again, I'm really hoping Mysteries Revised or a Hedgey book will shed more insight on this topic.
How do you create a ghost?
Insert knife here...
In terms of theology, it's likely up to you. One could argue that ALL a ghosts are on earth waiting for Revelations to occur. These ghosts, are not restless dead and are therefore not seen hanging out and haunting folk.
We obviously disagree on the distinction between ghosts and spirits, but I'll stick to my interpretation. Because of that, I feel that one can summon ghosts, but not create them. However I do feel that Hermetic magic can create a spirit, which is not a 'ghost.' These spirits that can be created have been detailed in the old Hedgey and Mysteries book. Again I'm hopeing the new Mysteries book will shed some insight into creatures of the air.
I think these (admittedly ArM4) passages may clarify things:
Per ArM4 Blood & Sand: The Levant Tribunal, page 68:
Sahir's (Levantine spirit masters) can summon Ghosts "whose bodies have not been given a Christian or Muslim burial, and Jewish ghosts who have been buried, but have been dead for less than a year (see Kaballah , pages 123-124".
Per ArM4 Kaballah: Mythic Judaism, pages 111-114, in the section on Jewish Necromancers (hedge magicians who summon ghosts to speak with them or command them):
"Any ghost currently wandering the earth, or any spirit (sic) whose body has not been given a proper burial, may be summoned."
In Greek myth, only the pagan "restless dead" who had not been given a proper burial could be summoned. This usually consisted of:
ahoroi: those killed before their time / before their natural lifespan, including specifically biaiothanatos: those who have been killed by violence in particular.
So basically, any ghost without a proper burial (cf Jewish ghosts above) can be summoned within the limits above IMO.
Both books BTW used similar mechanics and in fact the respective sections ae very useful for any would-be spirit diviner style necromancer:
"Assist me": ghosts uses an Ability they had in life
"Follow me": ghost follows the necromancer for Sun duration
"Immortalise me": subtract the ghost's Might magnitude from next ageing roll
"Journey:" ghost travels to anywhere the necromancer has an Arcane Connection
"Perform for me": ghost uses a Power or ABility for the necromancer
"Prophesy for me": ghost divines a question as if it had Might/5 Divination score
"Protect me": ghost resists one specific attack directed against the necromancer with its Might score
"Return peacefully": ghost returns from where summoned and cannot harm the necromancer unless commanded again
Sahirs could also command "Teach me" which forced the ghost to spend a season tutoring in an Ability it knows.
I'm hoping the revised Theurgy rules in TMRE will help clarify spirit mastery / necromancy for ArM5, but this might help for the moment.
IOSD doesn't actually create a ghost IMO, merely summons one of the existing ones vulnerable to being summoned. These ghosts could be seen with Second Sight when thye manifest, but are otherwise probably floating off in regiones or the Magic Realm (or perhaps Faerie Realm for pagan ghosts).
Summon, but not create. HoH:TL has several stories about Tremere necromancers who summon the restless Pagan dead - Guorna the fetid is referred to as one such magician and there was even a necromantic Prima. One of the spells in that section does exactly what you propose: "Call the Fallen Eagles from the Mist" is a Level 65 Rego Mentem ritual that summons pagan Roman legionnaires (stats given HoH:TL page 126).
I strongly doubt that this is meant to create ghosts but you could ask Timothy Ferguson, the author of the section.
In ArM4 Mysteries there were ways of creating theurgical spirits which may be revised in TMRE (we already have the Animae Magic Mystery in HoH:MC "Merinitiae" which allows the creation of faeries, so I don't see why not). These "spirits" are not ghosts however - I agree with Tuura here.
I strongly suggest you buy the HoH:TL book to help you flesh out your conception of a necromancer, which seems very much of the Graeco-Roman style diviner of spirits that Timothy has based the "new wave" Tremere on. I don't think you'd be disappointed.
As for historical sources, try "Witchcraft and Magic in Europe: Ancient Greece and Rome", Athlone Press, edited by Bengt Ankarloo and Stuart Clark. Well worth the read and you might be able to pick it to borrow up in a decent University Library. Along with Kieckhefer's "Magic in the Middle Ages", I've found it great for fleshing out ideas for Hermetic magi with a real Graeco-Roman bent. If you like the original Mysteries you'd like this - I'm hoping I can use it in conjunction with TMRE when it comes out.