If you attempt to cast a spell and for some reason, what you are doing will not work because of the requirements of the spell? 1) fail to cast the spell completely (not using the spell slot) OR 2) cast the spell, burn the spell slot and it has no effect OR?
I know there are several different flavors of this. I am mostly concerned when something is inherently not a valid target of the spell. For example, you try Charm Person, and they are not actually a humanoid (or hold person, or hold monster, etc). Or Catapult and the object you attempt to move is outside your weight range. In those cases I would think that the spell can't acquire that target and so isn't cast at all. In the case of something being immune to an effect, you could cast it, but it wouldn't work due to that immunity. Charm Person on an Elf... spell is cast, elf is immune. But again, really interested in the first case, what you are trying to do is either forbidden by the spell (like mage armor on someone wearing armor) or an invalid target or an invalid range (for whatever weird illusion reason).
A follow up question is --- do you burn your action if the spell won't cast at all?
In my games, I rule that there are two parts to the cast a spell action: casting a spell and targeting a spell - casting a spell means that the action and spell slot are used, even if it then transpires that there is no valid target.
As an example, casting charm person on a human noble, but not knowing that they're actually a shapechanged dragon, so the spell fails. The caster has no way of knowing that and, as a DM, you may even pretend to roll a saving throw for them. The catapult spell I'd rule would also be cast, then trying to move it, I'd describe the magical strain on the caster as they try their hardest to move the boulder, but it's just too heavy.
If it's something like casting mage armor on someone who is wearing armour, I would remind the player that their character knows that this won't work, so would they like to pick a different thing to do. If they insist, then sure, the spell is wasted.
Storm knight is a follow on to your rule that since targeting is separate being unable to target mean they should know that and be able to switch targets? It is magic after all. If it knows a target is valid, the spell should also know when invalid. The spell itself makes that determination so the caster should be aware it is an invalid target.
Coder, thanks. So if there is an optional rule, does that mean the default rule is that a slot isn't generally burned? Sigh. Annoying that this common, obvious, and fairly important thing is optional ruled
The books aren't officially specific on this to my knowledge, and as a DM I lean toward not having players' limited resources be able to be "wasted".
Like how a paladin doesn't have to declare their smite usage until they know they have hit, I don't have spellcasters burn a slot when there is no possibility of the spell in question actually doing something. Of course, the exact question of trying to cast a spell with a target limitation on a target that doesn't fit that limitation is a bit trickier - it's never come up at my table thus far, so I've not made a decision on it. Would I say "Nope. try something else because that spell won't work" or would I consider the something that spending the spell slot did to be revealing important information about the intended target by saying "You cast the spell, and yet it has no effect at all upon your target." I am not sure, but I'd probably go with the former.
Coder, thanks. So if there is an optional rule, does that mean the default rule is that a slot isn't generally burned? Sigh. Annoying that this common, obvious, and fairly important thing is optional ruled
There is no default rule. The rules in the core books don't address the possibility that you might pick an invalid target, so the DM decides what happens. Lead rules designer Jeremy Crawford talks about this in an episode of Dragon Talk. There's plenty of corner cases that can come up and they couldn't come up with a satisfying rule in time for the Player's Handbook, so they left it in the hands of the DM.
You have to consider at least 3 kinds of spells: spells that automatically affect chosen targets (e.g. Hold Person), spells that involve attack rolls (e.g. Guiding Bolt), and area spells that affect targets without choosing them (e.g. Fireball.) It doesn't make sense to let casters keep their slots for the latter two; the spell is going to happen whether you aim at the right things or not. You don't get to keep your spell slot if you miss Guiding Bolt at a valid target and miss so why would you keep it if you aim at a statue and hit? Likewise, you can fire a Fireball blindly and it'll explode whether there actually was an invisible creature there or not.
So that just leaves Hold Person-type spells, which don't produce anything if you pick the wrong target. Letting the caster keep their slot is generous but more complex rules-wise, while saying the slot is always wasted is harsher but simple and consistent.
The caster doesn't get back Fireball's slot if they cast it on creatures that are immune to fire. He didn't know (hopefully), and they were unaffected. Spell lost, he will know better next time.
I don't see a reason to treat situations like attempting Hold Person to a non-humanoid (or to the illusion of a guard!) any differently.
I also don't consider it a waste. It gives information ("why is that pebble weighing more than my weight limit?"), and that can make or break a quest - or a wizard; these guys thrive on knowledge.
It is a simple argument that if the spell requires a specific target or type be chosen, the spell cannot be cast if the target you chose does not meet that requirement. As each spell defines the individual use and rules for the spell, it would clearly be a call based on specific wording of each spell. For example, Mage Armor says it cannot be cast on someone wearing armor. You try to cast it on someone wearing armor, you did not meet the requirement to cast the spell, it is never cast. You shouldn't burn the slot. Because you simply did not meet the specific casting requirement in the spell text.
The rest of your takes either fall under normal rules for to hit or save or immunity that are actually written rules. Charm person is a great example.
You attempt to charm a humanoid you can see within range. This is a clear requirement. If what you picked isn't a humanoid, the spell just won't cast. Because... required that you target be humanoid. You also cant pick a humanoid you are actively touching but cant see... sorry seeing is a requirement. If you cant cast say burning hands without doing the spread hands thing "because the text says you have to" the you cant cast this without actually targeting s humanoid. Sure, they could be a humanoid immune to charm, and the cast spell fails because a specific rule says it did. Then they get a save to avoid if they aren't immune. Again written in text.
I think everyone is seriously overflowing the "super useful" information granted by telling a player. "Nope, the spell wont cast". And I think burning their action is enough price to pay for that glimmer of information. Taking a spell slot too is insane imo.
Well, you have a clear idea of what you prefer for your game. Adopt it (if you're the DM), or discuss it with your DM; it's a perfectly valid way to go with things.
Personally, I see spellcasting as a non-sentient means of enforcing your will. There are rules, and going against those rules is a waste of effort. Attempting to cast Magic Missile "at the darkness" won't result in the Weave telling you "sorry, can't do that, stop moving your arms and speaking in tongues". The wizard can certainly try to force the attempt, expending his energies (his slot), and, in the end, it will do nothing.
As such, when as a DM I tell someone "this isn't a valid target" for something the character knows isn't a valid target is just extending the courtesy to the player of not wasting his effort to something his character, with years of study and experience (or instinctive understanding) knows will be to no avail. If the character does not know his target isn't valid, I see no reason for this courtesy; they'll find out the hard way.
Note, in situations where character judgment may be better than player judgment, I may require a roll instead of letting a player expend themselves for no reason ("Roll a Wisdom check." 17 "Are you sure you want to cast Charm Person on him? The one you seek is a Doppelganger.").
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If you attempt to cast a spell and for some reason, what you are doing will not work because of the requirements of the spell?
1) fail to cast the spell completely (not using the spell slot)
OR
2) cast the spell, burn the spell slot and it has no effect
OR?
I know there are several different flavors of this. I am mostly concerned when something is inherently not a valid target of the spell. For example, you try Charm Person, and they are not actually a humanoid (or hold person, or hold monster, etc). Or Catapult and the object you attempt to move is outside your weight range. In those cases I would think that the spell can't acquire that target and so isn't cast at all.
In the case of something being immune to an effect, you could cast it, but it wouldn't work due to that immunity. Charm Person on an Elf... spell is cast, elf is immune.
But again, really interested in the first case, what you are trying to do is either forbidden by the spell (like mage armor on someone wearing armor) or an invalid target or an invalid range (for whatever weird illusion reason).
A follow up question is --- do you burn your action if the spell won't cast at all?
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D&D Beyond FoundersI'm not sure that the rules strictly cover this.
In my games, I rule that there are two parts to the cast a spell action: casting a spell and targeting a spell - casting a spell means that the action and spell slot are used, even if it then transpires that there is no valid target.
As an example, casting charm person on a human noble, but not knowing that they're actually a shapechanged dragon, so the spell fails. The caster has no way of knowing that and, as a DM, you may even pretend to roll a saving throw for them. The catapult spell I'd rule would also be cast, then trying to move it, I'd describe the magical strain on the caster as they try their hardest to move the boulder, but it's just too heavy.
If it's something like casting mage armor on someone who is wearing armour, I would remind the player that their character knows that this won't work, so would they like to pick a different thing to do. If they insist, then sure, the spell is wasted.
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The core rules don't address these situations. Xanathar's Guide to Everything has an optional rule which results in a wasted spell slot.
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Storm knight is a follow on to your rule that since targeting is separate being unable to target mean they should know that and be able to switch targets? It is magic after all. If it knows a target is valid, the spell should also know when invalid. The spell itself makes that determination so the caster should be aware it is an invalid target.
Coder, thanks. So if there is an optional rule, does that mean the default rule is that a slot isn't generally burned? Sigh. Annoying that this common, obvious, and fairly important thing is optional ruled
The books aren't officially specific on this to my knowledge, and as a DM I lean toward not having players' limited resources be able to be "wasted".
Like how a paladin doesn't have to declare their smite usage until they know they have hit, I don't have spellcasters burn a slot when there is no possibility of the spell in question actually doing something. Of course, the exact question of trying to cast a spell with a target limitation on a target that doesn't fit that limitation is a bit trickier - it's never come up at my table thus far, so I've not made a decision on it. Would I say "Nope. try something else because that spell won't work" or would I consider the something that spending the spell slot did to be revealing important information about the intended target by saying "You cast the spell, and yet it has no effect at all upon your target." I am not sure, but I'd probably go with the former.
There is no default rule. The rules in the core books don't address the possibility that you might pick an invalid target, so the DM decides what happens. Lead rules designer Jeremy Crawford talks about this in an episode of Dragon Talk. There's plenty of corner cases that can come up and they couldn't come up with a satisfying rule in time for the Player's Handbook, so they left it in the hands of the DM.
You have to consider at least 3 kinds of spells: spells that automatically affect chosen targets (e.g. Hold Person), spells that involve attack rolls (e.g. Guiding Bolt), and area spells that affect targets without choosing them (e.g. Fireball.) It doesn't make sense to let casters keep their slots for the latter two; the spell is going to happen whether you aim at the right things or not. You don't get to keep your spell slot if you miss Guiding Bolt at a valid target and miss so why would you keep it if you aim at a statue and hit? Likewise, you can fire a Fireball blindly and it'll explode whether there actually was an invisible creature there or not.
So that just leaves Hold Person-type spells, which don't produce anything if you pick the wrong target. Letting the caster keep their slot is generous but more complex rules-wise, while saying the slot is always wasted is harsher but simple and consistent.
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I'll agree with Coder.
The caster doesn't get back Fireball's slot if they cast it on creatures that are immune to fire. He didn't know (hopefully), and they were unaffected. Spell lost, he will know better next time.
I don't see a reason to treat situations like attempting Hold Person to a non-humanoid (or to the illusion of a guard!) any differently.
I also don't consider it a waste. It gives information ("why is that pebble weighing more than my weight limit?"), and that can make or break a quest - or a wizard; these guys thrive on knowledge.
It is a simple argument that if the spell requires a specific target or type be chosen, the spell cannot be cast if the target you chose does not meet that requirement. As each spell defines the individual use and rules for the spell, it would clearly be a call based on specific wording of each spell. For example, Mage Armor says it cannot be cast on someone wearing armor. You try to cast it on someone wearing armor, you did not meet the requirement to cast the spell, it is never cast. You shouldn't burn the slot. Because you simply did not meet the specific casting requirement in the spell text.
The rest of your takes either fall under normal rules for to hit or save or immunity that are actually written rules. Charm person is a great example.
You attempt to charm a humanoid you can see within range. This is a clear requirement. If what you picked isn't a humanoid, the spell just won't cast. Because... required that you target be humanoid. You also cant pick a humanoid you are actively touching but cant see... sorry seeing is a requirement. If you cant cast say burning hands without doing the spread hands thing "because the text says you have to" the you cant cast this without actually targeting s humanoid. Sure, they could be a humanoid immune to charm, and the cast spell fails because a specific rule says it did. Then they get a save to avoid if they aren't immune. Again written in text.
I think everyone is seriously overflowing the "super useful" information granted by telling a player. "Nope, the spell wont cast". And I think burning their action is enough price to pay for that glimmer of information. Taking a spell slot too is insane imo.
Well, you have a clear idea of what you prefer for your game. Adopt it (if you're the DM), or discuss it with your DM; it's a perfectly valid way to go with things.
Personally, I see spellcasting as a non-sentient means of enforcing your will. There are rules, and going against those rules is a waste of effort. Attempting to cast Magic Missile "at the darkness" won't result in the Weave telling you "sorry, can't do that, stop moving your arms and speaking in tongues". The wizard can certainly try to force the attempt, expending his energies (his slot), and, in the end, it will do nothing.
As such, when as a DM I tell someone "this isn't a valid target" for something the character knows isn't a valid target is just extending the courtesy to the player of not wasting his effort to something his character, with years of study and experience (or instinctive understanding) knows will be to no avail. If the character does not know his target isn't valid, I see no reason for this courtesy; they'll find out the hard way.
Note, in situations where character judgment may be better than player judgment, I may require a roll instead of letting a player expend themselves for no reason ("Roll a Wisdom check." 17 "Are you sure you want to cast Charm Person on him? The one you seek is a Doppelganger.").