Possessing a Demon

[Plane]

Originally Posted by Anthony

all spells in C&E and Mind Control should be considered mind-affecting.

Sense Foes (M44) and Sense Life (M45) ? 46's Lend Language seems like it would be (you're imparting knowledge: as with Gift of Letters) but I'm not sure about Borrow Language (as with Mind Search) is copying data from a mind affecting the mind if you don't actually change anything in it?

[Anthony]

Originally Posted by Plane

Sense Foes (M44) and Sense Life (M45) ? 46's Lend Language seems like it would be (you're imparting knowledge: as with Gift of Letters) but I'm not sure about Borrow Language (as with Mind Search) is copying data from a mind affecting the mind if you don't actually change anything in it?

I would say yes. It's pretty clearly not supposed to be possible to know if a demon is lying, for example.

[Black Leviathan]

Originally Posted by Anthony

Resisted by will is less important than it being C&E. Basically, all spells in C&E and Mind Control should be considered mind-affecting.

I'm sure there are some oddball spells in the category that wouldn't seem normal for resisting with your mind but a spell resisted by Will would seem to be exactly what defines "Mind Affecting"

[Plane]

Originally Posted by Anthony

I would say yes. It's pretty clearly not supposed to be possible to know if a demon is lying, for example.

Clearly where? M155 says their Acting skill is only 9.

Originally Posted by Black Leviathan

I'm sure there are some oddball spells in the category that wouldn't seem normal for resisting with your mind

but a spell resisted by Will would seem to be exactly what defines "Mind Affecting"

As pointed out earlier: Body-Reading, Transmogrification, Soul-Rider all use Will to resist and don't appare to actually control the mind in any way: they give data on the body, shapeshift the body, or give a feed to their sensory input.

[Anthony]

An obvious test for whether something is mind-affecting is "does it work on something that doesn't have a mind". Body-reading probably does. Soul rider probably does not.

[Plane]

"Affecting" is broader than "Controlling" but I think still implies you're doing something to alter the mind (rearrange it, force it to do something) not just glean information from it.

To use a book as an example, we should answer if it is 'affecting' a book to look at a page, to touch a page, to turn a page. Is this like in the sense that to affect a book you don't necessarily need to change what it says, but also to change its position in space? It's not like levitating someone's body (and their brain/mind along with it) is mind-affecting though.

[Anthony]

Originally Posted by Plane

"Affecting" is broader than "Controlling" but I think still implies you're doing something to alter the mind (rearrange it, force it to do something) not just glean information from it.

Well, I'm not aware of specific GURPS precedent on the issue (in 3e demons were just immune to all spells resisted by IQ), but if you're willing to look at other games, D&D was certainly willing to use 'mind-affecting' for information spells (e.g. detect thoughts).

[Plane]

Another interesting question is how the necromantic-spell Summon Demon (M155) which is a version of the gate-spell Planar Summons (M82) works to control them at all, since it's a contest against their will to get them to obey a command. The summoning spell itself is clearly mind-affecting magic.