Modify Memory to Manipulate Spells Known?

[Damon_Tor]

Memory, it seems to me, has mechanical implications for certain classes: classes which learn spells for example, presumably do so by remembering them.


Assuming I use a spell slot which accounts for the appropriate time-frame, could I use Modify Memory to make a spellcaster forget a spell they learned?
Could I change a spell they've learned to a different spell instead?
Could I trick them into casting the wrong spell by making them remember learning the components of a totally different spell in place of a spell they know?

[kazaryu]

Memory, it seems to me, has mechanical implications for certain classes: classes which learn spells for example, presumably do so by remembering them.


Assuming I use a spell slot which accounts for the appropriate time-frame, could I use Modify Memory to make a spellcaster forget a spell they learned?
Could I change a spell they've learned to a different spell instead?
Could I trick them into casting the wrong spell by making them remember learning the components of a totally different spell in place of a spell they know?


1. depends on how long it takes to 'learn' a spell. most DM's/world probably have ;learning a spell taking longer than 10 minutes.
2. strictly 'ask your DM' territory, as it involves things that aren't covered in the phb. You could theoretically convince a caster that they know a spell they don't, or convince them that they prepared a spell they didn't. However, as far as 'learning' spells (i.e. spontaneous casters) again, this harkens back to 'how long does it take to learn a spell'
3 you can, potentially convince a prepared caster that the spell components for a specific spell are different from the ones the memorized. However, the exact effect that has on their spell casting is entirely up to the DM.

basically: ask your DM.

but for me personally, the specific components of a spell aren't as important as what they mean to the caster. and as far as casting, the intent is ultimately the only thing that matters. the reason spell components are even a thing is that magic is something that mortal minds struggle to understand in any meaningful way. the use of magic is like...trying to flex a muscle your body isn't designed to flex, but you've managed to jury-rig a way to flex it. The spell components help them to put their mind/will in the right 'position' to flex the muscle in a particular way. so things like...messing with the memory of their spell components would do basically nothing in terms of casting. all you're doing is replacing the pneumonic they use to cast, not the 'position' that its designed to remind them of.

and for learned casters...no, you wouldn't be able to use modify memory to actually change their spell list. the best you could do is convince them they learned a spell that they didn't. and thus they may waste time trying to cast it. but IMO believing that you know how to cast a spell is not the same as actually knowing how to.

[Damon_Tor]

If I were making the call at my table, I'd say this:

There's more to learning a spell than memorization, but memorization is important. Also, learning to cast a spell takes longer than 10 minutes.
As such, you can theoretically cause a creature to forget how to cast a spell by erasing an important 10 minutes of their learning that spell and replacing it with something wrong.
However, to reliably sabotage their spellcasting, you would also need to erase/alter the memory of each time the creature successfully cast the spell since learning it, or they would simply think back to the way they've done it before and cast it correctly that way. I would rule this as a % chance of spell failure based on what % of their memories of the spell you've fiddled with. Pulling numbers out of nowhere in particular, I could count the memory of learning the spell at 10x the value of each subsequent casting. So if the target has cast a spell 10 times since they learned it and you sabotage the memory of learning the spell plus two instances of casting the spell, the target would have a 60% chance to cast it wrong each time they try to cast it.
You probably can't teach a new spell in this way, or trick them into casting a different spell simply by changing their memory of the components.

[Keltest]

I would allow 1 and 2, but probably not 3, and 2 would have the caveat that they need to be able to cast the spell and you would need it prepared (to know what to change it to).