Yup, I actually mean ReVi, thank you. I was thinking of 'Gather the Essence of the Beast' or similar spells. Brain fart!
That is the question, indeed.
But one of the advantages of "magic" is that we, as Players (yes, and even as StoryGuides), do not actually have any score in Magic Theory, so we don't understand exactly how it works, nor need to perfectly.
Q: How does Hermetic Magic work?
A: It works just fine, thanks for asking!
But there are 2 reasons for asking such - one is for a SG to have a concrete and self-consistent understanding of the rules so they can explain the world in those terms to Players (who may only be casually interested in such as an adventure dictates). But more is that the SG understand the world in a more abstract sense, especially when creating unusual situations - nothing is worse for any RP game than a world that is not the same in the minds of Players and Game Masters, or one where the rules of that world seem to change from session to session. (Subtleties, mysteries and "the unknown" aside - not every demon or faerie need work the same as the last one did, etc. But then the learned would know that as the rule.)
I'd have to agree with this interpretation. If vis were not essentially "magical" (at least at some level), a mage could not use it for magical purposes, which is where Hermetic Theory lives. In another thread I recently drew a distinction between a "Gifted" child, one who could become a Hermetic apprentice (even with a Flawed Gift), and a child who had been gifted (small "g") with Power from a different Realm - both powerful, both "magical" (small "m"), but the difference between a Magical Gift tainted/flawed by Fae or the Infernal, and a Fae or Infernal gift of Power is the difference between being able to perform Hermetic Magic and not, the diff between one Realm and another.
So maybe what we're seeing is another hiccup within Bonisagus' model, at least where InVi is concerned?
But all that doesn't mean that another model, interpretation or "understanding" isn't correct - self-consistency is the goal, so it all makes some sort of sense to the Players, and that it does, indeed, "work just fine".
CH, you are on fire!
10 topics answered by you this morning 
We will have reading material, that's sure
Ya, well... most of a year since I last logged on, so guess I've been saving up.
... and I been stiflin' m'self today, too!