What is intended by the term “unnatural” material in Ars Magica’s magic system, with regard to Creo of unnatural items? Well a long while back the 5e line editor clarified the intent, and I found it the other day while reading a tangential forum post.
The intent was for “unnatural” to have the same meaning in all guidelines. You can Creo flammable water. However, since it isn’t natural, you can’t use vis to make it endure; it’s only sustained by the magic, like Muto. There is no form for it; that’s what makes it unnatural. It wasn’t written as requiring a Muto requisite because you aren’t changing anything; you are bringing something into existence with those properties. Looking at it now, the magnitude boost is probably too small, however.
I don’t think this got heavily playtested, because looking at the rules shows that they aren’t as clear as they should be. That probably indicates that I and all the playtesters thought that the meaning was perfectly clear, without actually agreeing on what that meaning was. But since no-one saw a problem, no-one raised it for discussion.
Great answer and fair enough. Considering the implications of this statement, they directly match to the behaviour of spell effects that are traditionally in the purview of Muto, but also may be performed with Creo with an increase in spell level. IMHO Creo was never restricted to only creating things that were “real”, as we know when spells can create mythical creatures and all sorts of wonderful things outside a peasant’s mindset.
This does give Creo a wider scope than I first thought though to give it, which is a nice enhancement to it’s role intertwined amongst the 5x techniques.