Mages can get P.P.E. from other sources, however, and this is currently my source of contention. I had come to a conclusion some time ago that in order to use P.P.E. from an external source, the mage had to first use an action to pull the P.P.E. out of that source and into their own P.P.E. pool - a rule much more manageable to deal with when using the Rifts Book of Magic rules on page 21:
• A mage can hold up to 3× base P.P.E. for P.E. in minutes.
However, I can find no canon that backs this interpretation up with non-ritual spells. The closest thing I can find is sort of a backwards proof in the magic sections that describe rituals - for those spells, other sources can just be included in the ritual and used without having to first drain them. They're drained once the spell is cast. I say this is a "backwards" proof because I can interpret the inclusion of this rule in rituals to mean that it's exclusion in non-ritual spellcasting is significant. Which may or may not be true, depending on interpretation.
One notable thing this interpretation does is gives rituals a reason to be cast. If a mage can just use an external source to cast a spell he doesn't have the base P.P.E. for, then why would they elect to use a ritual? This was a problem to me, and my interpretation here solves it by making it impossible for a mage to cast any non-ritual spell whose P.P.E. cost is greater than 3× their P.P.E. base (or their P.P.E. base plus 3× their P.P.E. base, depending on how the Book of Magic rules are interpreted).
So for some examples...
- A mage wants to use a P.P.E. talisman to cast a spell. The mage spends an action taking the P.P.E. he wishes to use out of the talisman, and "holding" it as per the Book of Magic rules. Then his next actions(s) would be to cast the spell and fuel it with the P.P.E. he's holding.
- Two mages desire to have a spell cast. Neither of them have enough P.P.E, but together their combined P.P.E. is more than enough. The first mage allows the second mage to use an action to draw P.P.E. from him (up to 70% of the first mage's base amount), "holding" it as per the Book of Magic rules. The second mage then uses her next actions(s) to cast the spell and fuel it with the P.P.E. from her base, plus the P.P.E. she's holding.
- At a ley line a mage decides to use the energy from the line to fuel her next spell. She can only get so much P.P.E. per melee action, so she spends a number of actions absorbing that P.P.E., slowly building up the P.P.E. needed and "holding" it as per the Book of Magic rules. Once she has enough to cast the spell, she then spends her next actions(s) to cast the spell and fuel it with the P.P.E. she's been holding.
- Even if the energy was available after only one action of absorbing, the mage would've had to spend an action to absorb that energy, then begin casting the spell on the next action.
In none of these cases, however, do the rules actually require an action to be spent to acquire and "hold" the P.P.E. before the mage casts it. Have I made an error in my interpretation, and the mage should just be able to cast spells from the P.P.E. around him/her? If that's the case, is there a reason (canonically) to limit those spells' P.P.E. cost to less than the "Book of Magic 3× base" (or 3×base + base) holding P.P.E. rule?