So, here's my question. Under the description of Banishing, it says that a Spirit whose Services are reduced to 0 will attempt to depart to its home metaplane on its next action.
It then states "The banishing magician (or any magician within line of sight, for that matter,) can make a Summoning Test against the spirit before it departs, bringing the spirit into her own service instead. A spirit banished and then summoned this way can later be bound as well."
So, say you have a Tradition which doesn't summon Spirits of Air, but the Magician in question really, really wants a Spirit with the Movement power. Can she and a friend lurk in the Astral until a Spirit of Air comes by, have the friend nail it with a Banishment to drop its services to Zero, and then she nails it with a Summoning check to grab it?
That would seem unlikely, since the description of Summoning states (literally as the first line,) "A magician may only summon the chosen spirits of her tradition", but it seems that there might be some wiggle room between "call from the Astral Plane" and "grab something already here on Earth." If not by default (which I suspect to be the case,) could some Metamagic technique allow for pulling this stunt?
Or, failing those, can you mentally dominate a loose spirit to similar effect, commanding it to remain on this plane and use its powers as you please?