Ships and buildings: only T:Str or also T:Ind?

A ship or building can clearly be targeted through a T:Str spell (which also affects all of its contents). Can it also be targeted by a T:Ind spell, with the appropriate size modifiers? I'd say that if you can create a bridge at T:Ind (and a composite one - not just a solid chunk of wood) as per the core book, T:Ind should also work. Any canon examples?

I would say yes IF you did not want to effect any of the contents of the target. Like targeting a box but nothing in it.

Note that, obviously, building creation Rituals have T:Ind. But what if you wanted to move a ship (and, as a consequence, its cargo with it)? Would you need T:Str or would T:Ind be adequate?

I think T:Ind with size modifiers is just fine.

It's a fine rules point, but Individual is pretty limited with respect to people and stuff they carry. Structure target is designed to specifically enable you to affect the structure and its contents.

I'm not following your point. One can cast Lift the Dangling Puppet on a man in full armor and lift him (and by extension) his armor and anything he's carrying, because he's acting on the body.

The base size of Structure being already quite large (from a hut to a castle), I believe using Ind + size increment will lead to a similar size except for the smallest boat.
If you consider that the base Individual size for Herbam is 1 pace in every direction, it is too small for a boat.
Size +1 will be enough for a small fishing boat. Bigger than that, I would be tempted to impose structure just because of the complexity of the target (made of many different parts, possibly all affected by Herbam but of different natures: rope, different types of wood and so on).

With building, you will need to add extra-magnitude(s) to take in consideration the most challenging material (hard stone, but possibly iron since it is used to hold stones instead of cement in large buildings). Here if the spell is not of the right magnitude and is not able to affect the iron part, as GM, I will consider that the whole structure is made more fragile since magic was only targetting part of the structure and the parts that were not affected have been under heavy stress.

Or it might simply fail.

That magnitudes necessary to move a ship whether it is T:Structure or T:Ind with size magnitudes or T:Group with size magnitudes is something of a distinction without a difference. One might be able to save a magnitude with T:Ind, but I'd have to do the math...

If you wanted to move the ship through water you could use Ind with a size modifier. If you wanted to "teleport" the ship to a new port you need Structure.

The former effects the contents of the ship indirectly and the later effects it directly.

Structure is Rules as Intended.

Individual gets very messy for a variety of reasons, including:

Structures attached to the ground are not necessarily a discrete Individual (just as mountains are not). Conjure the Mystic Tower literally rises from the earth. Caves are rooms/structures that are part of the ground.

Many Structures may have been conjured with Group target magic. Conjure the Mystic Tower is a single block of stone, Wall of Wood is a single strange tree - both do this to employ Individual. A ship or bridge is made of many disparate parts (planks, tree trunks, ropes, iron nails, brass fittings, pitch) and probably considered Group for conjuration purposes. If care is taken you could conjure a ship-shaped single piece of wood which would be Individual, but obviously terribly unnatural. Note that Hermetic Projects uses Structure for Conjuration of the Seaworthy Cog, which is blatantly at odds with "Targets and Creo" of ArsM pg 113 (creating stuff must be Individual or Group). I mention this in case someone intends to use it as a counter-example, though the notion of using Structure with creo creation magic isn't a bad one, just one the main rules call out as NOT the way to do it.

The need to calculate the mass you can affect. Few GMs will let a base Individual spell move ten times that weight in stuff attached to it (see The Unseen Porter, which is a general 'move stuff' spell with defined limits). Does your Individual spell have enough 'oomph'?

Structure doesn't care about any of the above stuff (though teleporting a cave might get weird, I guess that's where you call in Part Target). Is it structure like? Then it works.

Individual magic might work in some cases, but that's not RAI and introduces tons of complications. So why bother? Structure is the elegant solution, it shouldn't be ignored to save a single magnitude in corner-case situations.

In this instance, we're not talking about a structure attached to the ground, but again, it's attached or built upon a foundation. Foundations in the day were rubble, IIRC, and it's a question as to whether the foundation and the structure upon which it's built are truly united. Caves are rooms, not structures in the Hermetic sense.

Conjuration of the Seaworthy Cog has been corrected via errata to T:Individual, with size modifiers.

Well, if the spell were a variant of The Unseen Porter with size modifiers, sure. Why not? Mind you, it can still only move one thing, though, if that thing as at the bottom of a pile and it supports the pile, you might very well be able to move it.

I never said structure should be ignored, and elegance is in the eye of the beholder. You might find it elegant, but someone else may not. Arguing the intent of the authors is fraught with risk, and it's about what is reasonable, or if not reasonable, comparable. I didn't do the math, but IIRC, whether you use T:Ind with sufficient size modifiers, T:Group with size modifiers (although this one is even less elegant as it presumes it moves all of the pieces together in a coordinated whole) or T:Structure (which might also require sufficient size modifiers depending on the desired target). Note that the errata for Conjuration of the Seaworthy Cog is T: Ind with Size +3 where before it was T:Structure (+3), so there really was no difference, and as I said it is largely a distinction without a difference.

ReHe with target individual moves the ship. The contents move with it through inertia, which means they slide towards the back of the ship (as they do when it's under sail, and probably with the same amount of success). ReHe individual move the ship too fast and you smash the cargo and crew into a paste at the back.

ReHe structure, on the other hand, affects the contents. Making it essentially inertia-less for the passengers and cargo.

I'm not a master of Aristotelian Physics, but I don't think this happens in Mythic Europe.

Well, I suppose if you apply casting requisites, otherwise, if the object isn't of the Form, then the spell by definition can't affect items of other Forms.

The title of the thread refers to both buildings and structures, and bridges were also referenced early in the thread. I agree not every structure is going to be united with the ground, but a anything with solid foundations or catacombs, deep pilings (like bridges), it gets harder to argue it's not part of the earth. As for caves, many will be rooms, but networks of caves could well be structures - either way, they're definitely part of the earth and not Individuals.

Well at least that's legal, though I think Group would have been a better target for something with so many moving parts.

Agreed, but the need to calculate whether or not the mass is more than the spell can manage is annoying (gameplay arguments ahoy!)

It's hardly risky to think that the designers intended us to affect structures with Structure Target rather than Individual. Or bounded areas with Boundary rather than Part or Group. These 'alternate choices' are typically just design hacks to squeeze out a Magnitude of difficulty - players and GMs are probably better served using the Central Rule (pg111) to adjust spell levels when something is thematically correct but is designed to use less power than normal.

This kind of misses the point. It's explicit that the designers intended us to affect structures with T:Structure, and the other examples you provide. But focusing on Structure, and coupling it with my point earlier to BlackLigre, T:Structure actually requires casting requisites to affect all of the items within. For example moving a ship with T:Structure, and everything on it would require at least terram, corpus, aquam requisites. This might very well make the spell unable to be cast, and I don't think that's the intent of T: Structure. See what I did there?

So, again, whether it's T:Structure or T:Individual, Size+3 it amounts to a distinction without a difference, and one avoids discussions of intent of the authors regarding whether T:Structure requires casting requisites to move the items within, at least to provide the inertia free effect that BlackLiger mentioned.

Pure hogwash, unless you can cite the author saying that.

Your interpretation is but one amongst many, have some respect for other's.

One of the risks being that the authors might show up and tell you what they intended.

Structure was primarily intended for targeting the things inside a structure, not the structure itself. Note that the first sentence of the description is "The spell affects everything within a single structure.". (ArM5, p. 113). The fact that it can also affect the structure itself is an afterthought. And, going beyond textual evidence, I designed the Target primarily to affect the things within the structure.

The goal was to avoid having any RDTs that relied on measurements of distance. Instead, they all rely on areas that are defined in the world, not by the spell. The exception is Part, which is harder than Individual, because we needed spells that affected part of the ground.

I would say that a ship is an Individual, as is a castle keep, but a cave complex is not. A full castle probably includes unlinked buildings, and so is a Group.

So, RAI is that ships and buildings themselves are primarily T:Ind, but can also be affected by T:Str.

David, I appreciate the clarification, but nearly every spell I could find in Ars Magica that targets a structure to affect the structure itself uses Structure target, including End of the Mighty Castle (main rulebook!), the spells for Hermetic Architecture (TMRE), the spells in Hermetic Projects. The ones that don't, like Conjure the Mystic Tower, are creation spells and can't use Structure. One counter-example I did find was The Great Rot, which can target a wooden structure or anything made of dead wood up to a certain size (Group).

Thus the confusion.

RAW may not be the same as RAI...