From before Merlin and since, some wizards have been able to tell the "true blood" of a king or other noble line, even if that branch of the family tree had been lost long ago.
If a Hermetic magus wanted to do likewise, with a specific bloodline, could they?Blood Will Tell
InCo Lvl 10+
5 Base ("sense a specific piece of info about a body")
+1 complex,
& etc for Range/Duration/Target*
(* There would be many Variations of this spell, depending what is perceived as needed. A +1 Touch/+0 Momentary/+0 Individual would be Lvl 15, while a +2 Sight/+2 Sun/+2 Group would be Lvl 40 for an all day crowd-searching type, etc.)I guess a large part of it is whether you accept "bloodline" as an integral aspect of the human body, but it certainly was in the Medieval Paradigm.
(Note that this does not tell "kingly qualities", which would require Mentem- it spots a descendant of a certain parentage, or family group. The spell would probably(?) have to be designed with that specific group in mind, or, if allowed at all, be much higher complexity for it to be variable.)
I suspect this might need to be subject to campaign-specific variants, depending on whether you feel the quality of bloodlines in your game are a purely physical entity - in which case corporem - or tied to the spirit - in which case mentem.
I could even imagine that kingship might be linked to the Soul, in which case it probably wouldn't be identifiable by hermetic magic. In which case, Merlin identified arthur's parentage through clever detective work, and then tried to pass it off as magic!
I think it should certainly work if the caster knew what to look for somehow. If he had an arcane connection to the blood line, for instance or knew the identity of the last true king. A spell like this at group should at the least tell you if two people are blood relations.
I can certainly see Merinita doing it with Faerie magic (target:bloodline). Although I think InCo would allow any magus to do it as long as he had a sample of the old kings body, I think it would thematically fit the Merenita best. Don't some tellings of the Merlin story make him part faerie anyway?
Altho' the original source material never states it as such, scholars generally concur that among the knights of the Round Table it was "Don't ask, don't tell." 8)
I'd have to agree that, without some starting point, such a spell would be a hard sell. Either first-hand familiarity with true-bloods, or some literal sample of the blood, or other such tangible connection to help design the spell in the first place (altho', if it was a tradition, the spell could then be taught down generations of wizards in that tradition.)
As to the question of Corpus vs. Mentem, the blood or the spirit...
Hmmm...
I could go either way. I like the idea of the blood, as some of true blood simply don't have the spirit of a king, tho' their lineage could put them in position to inherit such a title. And some who have the spirit of kingship don't have trueblood, (tho' that might be debated hotly at the time, and possibly even be out of Paradigm.)
But that's the sort of question this spell would answer, whether a kingly figure was deserving of a crown, to find an (alternate?) heir, or etc. It's not the spirit of a king that it detects, but the connection to a common significant ancestor.