[Taqwus]

At any given time, -all- Communion Slaves are considered slaves of -all- Communion Masters.

Note that you are only a Communion Slave/Master once you've cast that spell (unless it's automatic, which it is if you have the appropriate crystal matrix, or are a Pythium communicant). This can cause some issues if you have a particularly fast Communion Master.

For instance, suppose you're playing Pythium and have an Arch-Theurg leading a large communion of Theurgs, Theurg Acolytes, and Communicants. Suppose also that the Arch-Theurg is very experienced, and has the ability of Heroic Quickness from being in the Hall of Fame (or, more easily, by wearing boots of quickness). His first two spells scripted might be 'Communion Master' and, say, 'Summon Earth Power' (perhaps he's an earth mage, and you want the communicants to get reinvigoration).

Well, the Communicants will all get the 4 reinvig from SEP, since they're all automatically communion slaves. Any Theurgs/Theurg Acolytes that acted -before- the AT will also get it. Any only act later, however, will not (unless they have the crystal matrices) because they're not yet communion slaves; hence, these will not get the reinvigoration.

Now, if there were another AT who later casts Communion Master, both Communion Masters benefit fully from all the slaves -- and all the slaves will get fatigue from both ATs' casting, which could be rough in a long battle unless there's earth or nature magic (earthpower, relief) available.