A lake is a reasonable candidate for a T:Boundary spell - say an Aegis or some Intellego Ritual. Would such a spell include or exclude an island in the middle of the lake?
I'd say that one can cast the spell to either include or exclude the island, depending whether one includes in the Boundary just the "outer shore" of the lake, or the "inner shore" of the island too. Both seem mythically appropriate. But I am curious about your opinions!
I would choose whichever option does not invalidate a significant portion of potential Boundary spells. If I Muto Imaginem the lake's Boundary to make it look like a desert but the island is excluded from the effect, that would make it useless.
Regardless, I'm skeptical of an argument that the island isn't within the Boundary of the lake since it's in the middle of the lake. That's pretty much the definition of one thing being within the other thing.
Well, but if you are on the island, you are not in the lake.
In some sense the island is a "hole" in the lake.
I'm on an island in the lake. Where else would you say that the island is but "in the lake".
If I put a cupcake into a box and put that box into a chest that is enchanted to shrink everything placed within it by 1/100th, is my cupcake crushed because the box is a "hole" in the chest's effect -- the box holding the cupcake is clearly "in" the chest so it's effected.
Similarly, if I cast a big Structure spell with all the necessary Requisites to move the structure someplace else, I expect that whatever is in each Room will go along for the ride.
This is a simple Containers within Container Target situation; no need to argue it by semantics. Over time I've realized that pulling out a dictionary to resolve an Ars Magica rules question is an unrealized logical fallacy.
But, I'll go so far as to say that the entire Individual must be in the Container in the Container Target for it to be affected -- if you've only got a Part in there, it's not affected. So, if you shrink someone's ring their pinky is toast, but if you shrink a stuffed pastry the filling shrinks too.
The island is included. T:Boundary covers everything inside the boundary.
A Boundary is just one single boundary, not two or more. So you can't have both an outer and a non-connected inner border of a boundary
And really, it does not matter if the island is in the lake or not. It is inside the Boundary, and that is all that matters.
The outside of a lake is a natural boundary, much like the outside of the island is a natural boundary. You can fully consider the island to be within the boundary, or without, because either way what is bounded is clearly defined. Much like, I think, you could consider the dual layer of fortifications built by Ceasar arround Alesia to be a separate boundary that did not need to include the besieged city. As boundary spells are rituals, you have some time to define what the boundary you want is like, anyway, so long as the bounding is clear. And in some cases, it's possible you might get either of the lake minus the island or the island itself within a standard boundary, but you couldn't get both without adding a magnitude which your ritual might lack. My view is that the caster has the control on that, a boundary can have many shapes, and I don't see any reason to exclude a donut shape from the possibilities.
Well, but the issue here is which Rooms are part of the Structure. Imagine the typical medieval cloister: roughly speaking a square building, minus a square courtyard "hole" in the middle.
Now, the courtyard is definitely a Room according to the definition of ArM5.
But is it a Room belonging to the Structure? It can certainly be seen that way.
Yet it's equally natural to assume that it's not, and that the Structure is only the building itself while the "hole" in the middle does not count.
My first reaction is that it would depend in the nature of the effect. For example, a ReAq spell that turns the lake's water into beer might (or might not) affect a spring on the island. Intent when designing the effect is key, IMHO.
But yes, in most cases I would expect the island to be included in the boundary.
But the courtyard is not outside of the Structure. It being surrounded by the Structure is what makes it a courtyard. And certainly, anything surrounded by the Structure is inside the Structure.
... this is indeed veering into the dictionary fallacy.
That's exactly how I'd rule, modulo the spell itself including some reason to not allow the option.
I would allow for a spell to be designed for either or- but generally I'd say the island is within the boundary by definition. A spell excluding such would be an intentional design choice by the magus, not a standard (and I might inflict +1 complex mag for it).
If it effects everything within the boundary of the lake, then that includes the island. Whether it is in the body of water is irrelevant- the boundary is defined by the outer boundary of the lake, not whether something is inside the lake (which would probably be a seperate target on its own- or maybe Room if you get flexible and define the surface of the water as the "roof"...).
Similarly- a person hiding in a box in a room that has a Room target spell casted still falls within the spell's purview (assuming they are an applicable target in the first place). Simply being within a different Room inside the Room doesn't protect them- though that does sound like a fun faerie power.