There is a new player in our group, and he wanted to create a Mentem spell that will allow him to create personalities in people.
Naturally, I looked through the Mentem guidelines to try and find the base spell level, but could fing nothing that relates to personalities. Is this because the personality is considered an essential nature or a part of the soul?
Thanks
By personalities you mean personality traits?
There is some spell who can give a character a +3 in brave or so... but i don't remember where they are.
No, I mean the actuall personality of the person...
Just to muddy the waters with my two pence:
Is 'personality', as we understand it today, something inherent within a person -- that is, tied to their soul -- or not? The reason for this question is that if the answer is 'Yes', then a magus can't (presently) create a new personality out of magic, because personality is part of a soul, and what he'd be trying to do is create a new soul. Something the Limit of the Soul currently restricts magi from doing.
Another way of thinking about it is: Are you trying to 'break' the existing personality by causing another one to emerge? If so, a PeMe or a ReMe spell might do. A PeMe spell would result in a slightly 'messier' and random personality emerging (as you would be 'breaking' an existing one), while a ReMe spell could result in twisting and recasting an existing personality by enhancing or diminishing certain aspects of a person's personality so as to bring out what appears to be a different individual.
Finally, there is always the idea of a ghost or some sort of spirit inhabiting the person's body. The spirit would take control and speak with its own voice and personality, which would look like a personality shift to an outside observer. This would be a ReMe spell.
I guess it all depends on how you interpret what 'personality' is, and how it would fit within the medieval paradigm. I'd think that the last option -- possession by spirits -- would be a common explanation and is something well within Hermetic limits.
That's exactly what he meant.
What do you think the bae level should be?
I think that you should go with "control an unnatural emotion", base 10, but increase the spell by a few magnitudes to represent affecting several emotions simultaneously. As a formulaic spell, it will create a particular sort of change whenever it is applied, always - perhaps reversing the person's Brave, Curious, and Pious traits, for example, or switching the largest and smallest personality traits. No flexibility.
Using this baseline:
Starting Level: 10
+2 Magnitudes for manipulating multiple emotions/personality traits simultaneously
+2 Magnitudes to go from Personal to Voice range
+2 Magnitudes to go from Momentary to Sun duration
That works out to a level 40 ReMe spell. I hope he's got a good ReMe lab total!
If you're looking for the bargain bin version, you could try starting at level 3 (Make a subtle different in a target's mental state). That wouldn't express itself as full blown separate personalities, but it might make them act differently than they might otherwise do so.
This would work out to:
Starting Level: 3
+2 Magnitudes to go from Personal to Voice range
+2 Magnitudes to go from Momentary to Sun duration
Final level: 15 (which might be more attainable). Wholesale control and influence if someone's mind like what your player is thinking requires a dedicated Mentem specialist.
Well, I finally had to register just so I could jump in on this question. I've been involved with ArM off and on since the 2nd ed. but I'm still trying to get my feet planted with the 5th ed. so, I've been lurking for some time now.
Reinmar raised an interesting question and if I were the SG I would rule such a spell as breaking hermetic law . The reason is the Greek idea of "nous". Plato viewed this as the immortal rational part of the soul. In the Eastern Church this same "nous" is viewed as the "mind of the heart" which has implications for how the Trinity is understood/viewed. In short the "nous" is the intellect or higher mind or another way of looking at it is it makes us the who we are. It could even be argued that our personality is a manifestation of our soul projecting itself to those around us and so our soul is our personality.
If my player insisted on pursuing this line I would classify it as infernal, i.e. possession 
, and see if they still wanted to explore the idea. 
Just my 2 cents. 
Out of curiousity, could this sort of thing also be done by playing with the balance of humours within a person by way of Rego Corpus?
Art & Academe says that this would probably need some sort of Breakthrough. Can't give you a page reference just now, but it is where the humours are described.
Mark